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Selective breeding is a potent method for developing strains with enhanced traits. This study compared the growth performance and stress responses of the genetically improved Abbassa Nile tilapia strain (G9; GIANT-G9) with a local commercial strain over 12 weeks, followed by exposure to stressors including high ammonia (10 mg TAN/L), elevated temperature (37 °C), and both for three days. The GIANT-G9 showed superior growth, including greater weight gain, final weight, length gain, specific growth rate, and protein efficiency ratio, as well as a lower feed conversion ratio and condition factor compared to the commercial strain. The expression of growth hormone in the brain of the GIANT-G9 increased significantly after 6 weeks, although it slightly decreased after 12 weeks. Growth hormone receptor 1 expression also increased significantly after 6 weeks. Muscle insulin-like growth factors (igf1 and igf2) levels up-regulated significantly only after 12 weeks in the GIANT-G9. Under stress, serum enzymes (alanine aminotransferase, aspartate aminotransferase, and alkaline phosphatase (ALP)) were significantly higher in the GIANT-G9, while the commercial strain had lower levels. No significant changes were observed in liver ALP activity among stressed strains. Under stress, the GIANT-G9 exhibited marked upregulation of splenic Toll-like receptors (tlr2, tlr9, tlr21), myeloid differentiation primary response protein 88 (myd88), nuclear factor kappa B (nf-κB), interleukin (il) 1β, and il6. Notably, il6 expression was higher than il1β in the spleen, with the opposite pattern in the head kidney. In response to immune stimulation, globulin levels significantly increased in the GIANT-G9 but with similar values to the stressed commercial strain. Myostatin expression increased in the spleen of the stressed GIANT-G9. The commercial strain exhibited the best liver catalase and superoxide dismutase activities under stress, while the GIANT-G9 showed increased liver glutathione-S-transferase (GST) activity after exposure to ammonia and temperature stress. Serum lysozyme activity increased in the stressed commercial strain and under temperature stress in the GIANT-G9 but decreased under other stress conditions. Overall, the stressed commercial strain demonstrated higher survivability than the stressed GIANT-G9. The study revealed significant interactions between strains and stress factors. The GIANT-G9 exhibited higher growth rates but lower antioxidant and immune capacities compared to the commercial strain at the juvenile stage of life and production cycle., Competing Interests: Declarations. Ethics approval: The experiment and animal management protocols were approved by the Faculty of Fish Resources at Suez University, Suez, Egypt (Approval number 07/05/2024/10). The study was conducted in accordance with national and international regulations and guidelines, including the ARRIVE guidelines ( https://arriveguidelines.org/ ). Consent for publication: Not applicable. Competing interests: The authors declare no competing interests, except that Dr. Ahmed Nasr-Allah is the Country Director of WorldFish– Egypt. We affirm that this competing interest does not compromise the integrity of the research findings presented in the manuscript., (© 2025. The Author(s).)

Aggression is ubiquitous among social species and can function to maintain social dominance hierarchies. The African cichlid fish Astatotilapia burtoni is an ideal study species for studying aggression due to their dominance hierarchy and robust behavioral repertoire. To further understand the potential sex differences in aggression in this species, we characterized aggression in male and female A. burtoni in a mirror assay. We then quantified neural activation patterns in brain regions of the social behavior network (SBN) to investigate if differences in behavior are reflected in the brain with immunohistochemistry by detecting the phosphorylated ribosome marker phospho-S6 ribosomal protein (pS6), a marker for neural activation. We found that A. burtoni perform both identical and sex-specific aggressive behaviors in response to a mirror assay. Females had greater pS6 immunoreactivity than males in the Vv (ventral part of the ventral telencephalon), a homolog of the lateral septum in mammals. Males but not females had higher pS6 immunoreactivity in the ATn after the aggression assay. The ATn (anterior tuberal nucleus) is a homolog of the ventromedial hypothalamus in mammals, which is strongly implicated in the regulation of aggression in males. Several regions also have higher pS6 immunoreactivity in negative controls than fish exposed to a mirror, implicating a role for inhibitory neural processes in suppressing aggression until a relevant stimulus is present. Male and female A. burtoni display both similar and different behavioral patterns in aggression in response to a mirror assay. There are also sex differences in the corresponding neural activation patterns in the SBN. In mirror males but not females, the ATn clusters with the POA, revealing a functional connectivity of these regions that is triggered in an aggressive context in males. These findings suggest that distinct neural circuitry underlie aggressive behavior in male and female A. burtoni, serving as a foundation for future work investigating the molecular and neural underpinnings of sex differences in behavior in this species to reveal fundamental insights into understanding aggression., Competing Interests: Declarations. Ethics approval and consent to participate: Experimental procedures were conducted according to the ethical guidelines for the care and use of laboratory animals. Experiments were approved by the University of Houston Institutional Animal Care and Use Committee (Protocol #202000001). Competing interests: The authors declare no competing interests., (© 2024. The Author(s).)

Sensory processing of communication stimuli is essential for the survival of organisms across all evolutionary branches. Multimodal signaling, the use of multiple sensory systems is crucial in this process, but little is known about the relative importance of different senses used during aggression. We used the African cichlid fish, Astatotilapia burtoni, to test how visual and chemosensory signals in male-male interactions influence behavior. Males of this species exist in a dominance hierarchy, where brightly colored dominant individuals aggressively defend territories for reproductive activities. Focal males were presented with visual and chemosensory signals from other males either alone (unimodal) or together (bimodal). We found that vision is necessary for males to engage in aggressive behaviors such as frontal displays, lateral displays, and border fights. While chemical signals alone did not evoke aggressive behaviors, we find slight reductions of some aggressive behaviors when bimodal stimuli are provided. This study is the first to examine how visual-chemosensory signaling impacts male-male aggressive behavior in A. burtoni and provides insight on how these signaling modalities mediate territorial interactions., (© 2024 Wiley Periodicals LLC.)

The evolution of sexual dimorphism is widely acknowledged as a manifestation of sex-specific genetic architecture. Although empirical studies suggested that sexual dimorphism evolves as a joint consequence of constraints arising from genetic architecture and sexually divergent selection, it remains unclear whether and how these established microevolutionary processes scale up to the macroevolutionary patterns of sexual dimorphism among taxa. Here, we studied how sexual selection and parental care drive sexual dimorphism in cichlid fishes from Lake Tanganyika. We found that male-male competition, female choice, and maternal mouthbrooding are associated with sexual dimorphism in body length, body colour, and head length, respectively, despite strong allometric relationships between body length and head length. Within-species (static) allometry of head length on body length evolved as sex-specific responses to mouthbrooding, where females evolved higher intercepts while males evolved steeper slopes. Thus, selection to increase mouth size in mouthbrooders may have broken down and reorganized the pattern of allometric constraints that are inherently strong and concordant between sexes. Furthermore, sex-specific responses to mouthbrooding left a remarkably clear signature on the macroevolutionary pattern, resulting in a decoupling of co-evolution in parameters of static allometries between sexes observed exclusively within maternal mouthbrooders. Our study provides multiple lines of evidence that are consistent with the idea that macroevolutionary patterns of sexual dimorphism in Lake Tanganyika cichlids result from sexually divergent selection. Our approach illustrates that an examination of within-population phenotypic variance in the phylogenetic comparative framework may facilitate nuanced understandings of how macroevolutionary patterns are generated by underlying microevolutionary processes., (© The Author(s) 2024. Published by Oxford University Press on behalf of the European Society of Evolutionary Biology.)

Behavioural flexibility plays a major role in the way animals cope with novel situations, and physiological stress responses are adaptive and highly efficient mechanisms to cope with unpredictable events. Previous studies investigating the role of stress responses in mediating behavioural flexibility were mostly done in laboratory rodents using stressors and cognitive challenges unrelated to the ecology of the species. To better understand how stress mediates behavioural flexibility in a natural context, direct manipulations of the stress response and cognitive tests in ecologically relevant contexts are needed. To this aim, we pharmacologically blocked glucocorticoid receptors (GR) in adult Neolamprologus pulcher using a minimally invasive application of a GR antagonist. GR blockade prevents the recovery after a stressful event, which we predicted to impair behavioural flexibility. After the application of the GR antagonist, we repeatedly exposed fish to a predator and tested their behavioural flexibility using a detour task, i.e. fish had to find a new, longer route to the shelter when the shortest route was blocked. While the latencies to find the shelter were not different between treatments, GR blocked fish showed more failed attempts during the detour tasks than control fish. Furthermore, weak performance during the detour tasks was accompanied by an increase of fear related behaviours. This suggests that blocking GR changed the perception of fear and resulted in an impaired behavioural flexibility. Therefore, our results support a potential link between the capacity to recover from stressors and behavioural flexibility in N. pulcher with potential consequences for an effective and adaptive coping with changing environments., Competing Interests: Declaration of competing interest We declare no conflict of interest., (Copyright © 2024 The Author(s). Published by Elsevier Inc. All rights reserved.)

The potential of bitter orange peel powder (BOPP) as a nutritional strategy for fish was investigated in Nile tilapia. A total of 120 juveniles with an average initial weight of 9.8 ± 0.7 g were divided into four groups, replicated three times, resulting in 12 experimental units (60 L each) at a stocking density of 1.63 g of fish per liter. Productive parameters, whole-body composition, blood biochemistry, erythroid morphometry, intestinal histology, and heat tolerance were assessed in the juveniles subjected to one of the following treatments: non-supplemented basal diet (control group); basal diet with BOPP at 10 g/kg (BOPP10 group); basal diet with BOPP at 20 g/kg (BOPP20 group); and basal diet with BOPP at 40 g/kg (BOPP40 group). The BOPP additive had a positive influence on Nile tilapia growth, as final weight and weight gain were greater in all BOPP-treated fish, despite the reduction in crude protein in BOPP10 and BOPP20 groups. Fish receiving BOPP40 had an increase in total lipids and showed the highest levels of triglycerides and total cholesterol. Villi development was greater in the tilapia given BOPP10. It may be concluded that BOPP presented the most promising results for Nile tilapia juveniles when used at 10 g/kg diet. Regarding the erythroid morphometry, there was a general increase in nuclear and cytoplasmic areas in BOPP-fed tilapia; this seems to be the first report on the direct impact of the inclusion of functional additives in fish diet upon such parameters. As concerns the thermal tolerance evaluated at the end of the feeding trial, no differences were registered among the experimental groups. Thus, BOPP represents a feasible alternative ingredient to be explored in fish nutrition, since orange peel is a natural low-cost source of essential nutrients and valuable bioactive compounds., Competing Interests: Declarations Competing interests The authors have no relevant financial or non-financial interests to disclose. Ethical approval This research followed the guidelines laid down by the National Council for the Control of Animal Experimentation (CONCEA)—Normative Resolutions nº 34 and nº 44, and by the Brazilian Council of Veterinary Medicine—Resolution nº 879, which regulate animal experimentation and welfare. All experimental work was approved by the Ethics Committee on Animal Use of the Farroupilha Federal Institute—CEUA/IFFar (protocol nº. 5922130421)., (© 2024. The Author(s), under exclusive licence to Springer Nature B.V.)

This study delves into the early development of Vieja fenestrata (Cichlidae), with a specific focus on the description of external morphological and morphometric changes, and growth patterns from hatching to the loss of larval characters under controlled laboratory conditions at a temperature of 28°C. Asynchronous hatching was observed between 58 and 60 h postfertilization, with the posterior body emerging first. Over 14 days, significant morphological, physiological, and behavioral changes were observed, revealing a complex developmental trajectory. The initial developmental phases were characterized by rapid vascularization, fin differentiation, and heightened activity, and the subsequent days witnessed the flexion of the notochord, emergence of swim bladder functionality, and transition to exogenous feeding. Maturation progressed with the absorption of the yolk sac, regression of cement glands, and fin ray development, culminating in metamorphosis by 14 days post-hatching. Throughout this period, evolving pigmentation patterns and structural adaptations highlight the species' adaptive strategies. During the larval period of V. fenestrata, substantial changes in morphological proportions were observed. Before the inflection, tail length, trunk length, and body depth had negative allometric growth, and head length, eye diameter, and snout length had positive allometric growth. After the inflection, body depth and snout length showed positive allometric growth; head length and trunk length exhibited isometric growth, whereas tail length and eye diameter demonstrated negative allometric growth. These findings contribute insights into the intricate developmental dynamics of V. fenestrata. Moreover, further research may explore these developmental dynamics' ecological and evolutionary implications., (© 2024 The Author(s). Journal of Fish Biology published by John Wiley & Sons Ltd on behalf of Fisheries Society of the British Isles.)

Exposure to environmentally relevant levels of settleable atmospheric particulate matter (SePM) limits the aerobic performance of inactive healthy adult fish. We evaluated the gill morpho-functional impacts (gill structure and ionic balance) caused by SePM exposure (96 h) in Nile tilapia when fish is impelled to maximal aerobic swimming effort. In control fish, swimming reduced epithelial filament thickness (EFT, 25 %), increased the distance between lamellae (DL, 21 %), and reduced the plasma Na + (5 %). In resting fish, SePM exposure increased EFT (11 %), reduced DL (30 %), lamellar height (LH, 18 %), and plasma Na + (4 %), whereas increased Cl - and K + (8 % and 20 %). In SePM-exposure fish, swimming reduced EFT (40 %), increased DL (30 %) and LH (30 %), while reduced Na + and Cl - (9 % and 18 %), and increased K + when compared to inactive SePM-exposed fish. These morpho-functional limitations may compromise whole-body maintenance and swimming recovery, affecting the fish ability to perform at higher activity levels., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier B.V. All rights reserved.)

Previous research has highlighted the significant role of progestins and glucocorticoids in fish oocyte maturation and ovulation. To clarify the molecular mechanisms underlying these processes, comprehensive investigations were conducted using a cyp17a2 mutant Nile tilapia ( Oreochromis niloticus ) model. Analysis revealed pronounced Cyp17a2 expression in ovarian somatic cells of the tilapia. Female cyp17a2 -deficient mutants exhibited markedly reduced levels of 17,20β-dihydroxy-4-pregnen-3-one (DHP) and cortisol/cortisone, leading to delayed meiotic initiation and impaired oocyte maturation and spawning. Notably, supplementation with human chorionic gonadotrophin (hCG), DHP, and cortisol effectively induced germinal vesicle breakdown (GVBD) and facilitated oocyte release with follicular cell layers in cyp17a2 -/- females. Additionally, cyp17a2 -/- and rescued cyp17a2 -/- females showed elevated transcription of steroidogenic enzymes involved in 17β-estradiol (E2) production compared to spawning wild-type females. Moreover, the reduction in Akt phosphorylation observed in cyp17a2 -deficient females and upon inhibitor treatment impaired hCG-induced oocyte maturation. Conversely, activation of the phosphoinositide 3-kinase/protein kinase B (PI3K-Akt) signaling pathway partially rescued the oocyte maturation impairment caused by cyp17a2 mutation. Overall, these findings provide functional evidence supporting the critical role of Cyp17a2 in DHP and cortisol biosynthesis, which, in turn, facilitates oocyte maturation and ovulation through activation of the PI3K-Akt signaling pathway in fish.

Background: Water temperature and feeding frequency are critical abiotic factors regulating the growth and immune function of aquatic organisms. This study investigated the effects of water temperature and feeding frequency on growth and immune function in Nile tilapia (Oreochromis niloticus) over two months. A total of 360 juvenile fish (average weight: 20.00 ± 1.26 g) were divided into six groups, each with three replicates, based on a combination of three water temperatures (26, 28, and 30 °C) and two feeding frequencies (either 1 or 2 meals per day)., Results: At 30 ºC and 28 ºC, water electrical conductivity and total dissolved salts increased, while total ammonia nitrogen and dissolved oxygen rose slightly in groups fed twice daily, with a significant interaction between temperature and feeding frequency. The group at 30 ºC with two meals per day showed the highest final body weight (FBW). The interaction between temperature and feeding frequency significantly influenced FBW, total feed intake, and body thickness. Fish at 30 ºC exhibited upregulated hepatic growth hormone receptor 1 and insulin-like growth factor 1, while those at 28 ºC with one meal per day, as well as those at 30 ºC regardless of meal frequency, also showed increased expression of hepatic fatty acid binding protein and intestinal cluster of differentiation 36. Fish at 30 ºC had upregulated leptin levels and downregulated cholecystokinin, while those at 26 ºC displayed the opposite trend, particularly with one meal daily. Higher temperatures significantly boosted serum IgM, superoxide dismutase (SOD), and lysozyme (LYZ) levels, with meal frequency also affecting malondialdehyde, IgM, and SOD levels. Additionally, 30 ºC enhanced the hepatic expression of mucin-like protein (muc), oligo-peptide transporter 1 (pept1), interleukin 1, nf-κB, complement C3, lyz, sod, catalase, and glutathione peroxidase, with twice-daily meals having a more pronounced effect. Conversely, 28 ºC with one meal per day upregulated some of these genes, such as muc, pept1, and sod., Conclusions: Overall, 30 ºC with two meals per day significantly improved the growth and health of juvenile Nile tilapia, while 28 ºC with two meals maintained satisfactory performance., Competing Interests: Declarations Ethics approval The study was conducted at the Department of Aquaculture, Faculty of Aquatic and Fisheries Sciences, Kafrelsheikh University, Egypt. It was reviewed and approved by Kafrelsheikh University’s Ethical Committee under approval number KFS-IACUC/176/2024. The study adhered to the regulations and ethical guidelines outlined in ARRIVE (https://arriveguidelines.org/). Consent for publication Not applicable. Competing interests The authors declare no competing interests., (© 2024. The Author(s).)

The Nile Tilapia (Oreochromis niloticus) evolved in warm, freshwater rivers, but possesses a broad physiological tolerance to a range of environmental conditions. Due to this hardiness and resilience, this species has been successfully introduced to regions widely outside of its native range. Here, we examine the impact of temperature and salinity variation on this species at the sub-lethal level. Specifically, Nile Tilapia were exposed to two temperatures (21 °C or 14 °C) and three salinities (0, 16, 34 ppt) for 1-h. Given their native habitat, the 21 °C / 0 ppt exposure was considered the control condition. Both cell cycle arrest and apoptosis represent sub-lethal but deleterious responses to environmental stress. Flow cytometry was used to assess the percentage of cells in a given stage of the cell cycle as a metric of cell cycle arrest in spleen and liver. Percentage of apoptotic cells were also quantified. Spleen was more sensitive to cold stress, demonstrating an increase in cells in the G2/M phase after experimental treatment. Liver, however, was more sensitive to salinity stress, with a significant increase in cells stalled in G2/M phase at higher salinities, which is in keeping with the freshwater evolutionary history of the species. A modest apoptotic signal was observed in liver but not in spleen. Together, these findings demonstrate that even short, acute exposures to cold temperatures and elevated salinity can cause sub-lethal damage in a species that is otherwise tolerant of environmental stress at the whole organism level., Competing Interests: Declaration of competing interest The authors declare the following financial interests/personal relationships which may be considered as potential competing interests: The author is an Associate Editor for Comparative Biochemistry and Physiology but was not involved in the decision to publish this article., (Copyright © 2024 The Authors. Published by Elsevier Inc. All rights reserved.)

In the aquatic farming industry, understanding the factors affecting fish behavior is crucial, particularly in response to infections that compromise welfare and productivity. Swimming performance is a key life history trait critical to their ecology. This study explores the swimming behavior imbalance in Nile tilapia (Oreochromis niloticus, GIFT) post-infection with Streptococcus agalactiae (GBS), a common pathogen responsible for significant losses in aquaculture. We focused on how the microbiota-gut-brain axis influences the behavioral response of tilapia to GBS infection. Behavioral changes were quantified by measuring collision times and swimming speeds, which decreased significantly following infection. This behavioral downturn is mediated by alterations in the microbiota-gut-brain axis, evidenced by increased levels of monoamine neurotransmitters (serotonin, norepinephrine, and dopamine) in the brain and intestinal tissues. The study utilized pharmacological agents, the 5-HT 1A receptor agonist (8-OH-DPAT) and antagonist (WAY-100635), to investigate their efficacy in mitigating these behavioral and biochemical changes. Both agents partially restored normal behavior by adjusting neurotransmitter concentrations disrupted by GBS infection. Additionally, a notable increase in the relative abundance of Streptococcus within the gut microbiota of infected fish highlights the potential role of specific bacterial populations in influencing host behavior. This research provides novel insights into the complex interactions between pathogen-induced gut microbiota changes and Nile tilapia's behavioral outcomes, highlighting potential avenues for improving fish health management through microbiota-targeted interventions., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Inc. All rights reserved.)

The aim of this study was to develop a feeding protocol for the larviculture of Apistogramma cacatuoides, using the histological approach to larval nutrition conditions. For this, three experiments were carried out. Experiment 1 was carried out in a randomized design to determine the optimal amount of Artemia nauplii (AN) per larva, and three treatments were evaluated: P1-feeding with 25 A. nauplii per larva (AN/L) during the first 5 days, followed by 50 AN/L from the 6th to the 10th day and 100 AN/L from the 11th to the 20th day; P2 and P3-37 and 50 AN/L during the first 5 days, 75 and 100 AN/L from the 6th to the 10th day and 150 and 200 AN/L from the 11th to the 20th day. Experiment 2 was carried out in a randomized design to determine the daily frequency of feeding and evaluated four feeding frequencies: F1-feeding only once a day (09:00); (F2)-feeding twice a day (09:00 and 17:00); F3-feeding three times a day (09:00, 11:30 and 17:00); and F4-feeding four times a day (09:00, 11: 30, 14:00 and 17:00). Experiment 3 lasted 40 days and was conducted in a randomized design to evaluate three periods for the beginning of the feeding transition: WE10:AN for 10 days, followed by 3 days of co-feeding and commercial feed until the end of the experimental period; WE15:AN for 15 days, followed by 3 days of co-feeding and commercial feed; WE20:AN for 20 days, followed by 3 days of co-feeding and commercial feed. The results of this study showed that, for the best development of the larvae, they should receive the feeding protocol 50-100-200 AN/L (P3) until the 20th day of exogenous feeding. From the 21st day, the transition to inert food should begin with 3 days of co-feeding, and feeding during larviculture should be carried out at a frequency of twice a day; this protocol provided a good nutritional status for the larvae, as shown by the histological approach., (© 2024 Wiley‐VCH GmbH. Published by John Wiley & Sons Ltd.)

Symphysodon discus is known in the world of aquariums for its market value, beauty, and behavior. However, more substantial information about its physiology and biology must be available, which can hinder its development and maintenance in breeding systems. The study evaluated the blood biochemistry and erythrogram of 20 specimens of S. discus captured in the municipality of Barcelos, Amazonas, with an average weight of 89.80 ± 7.13 g and an average length of 13.48 ± 0.55 cm. The erythrogram evaluated variables such as hematocrit (Ht), hemoglobin (Hb), red blood cell count (RBC), mean corpuscular volume (MCV), mean corpuscular hemoglobin (MCH), and mean corpuscular hemoglobin concentration (MCHC). Blood biochemistry was analyzed, including cholesterol levels, total proteins, triglycerides, glucose, urea, and chlorides. Intra-specific variations were observed between the surveyed individuals about the Hb, MCV, and MCH values. The values of triglycerides, cholesterol, and chlorides were elevated compared to other cichlids. This study may be useful to serve as a parameter to indicate the normal health conditions of this Amazonian cichlid. It can be applied in studies for ornamental fish farming and actions for managing and conserving the species.

Low temperatures significantly influence feeding behavior in ectothermic vertebrates, but the underlying mechanisms remain elusive. This study investigated the role of transient receptor potential ankyrin 1 (TRPA1) channels in mediating the appetite-suppressing effects of low temperature in Nile tilapia. TRPA1 was found to be highly expressed in the hypothalamus and co-localized with neuropeptide Y (NPY) neurons. Exposure to low temperatures reduced feeding frequency and increased TRPA1 expression. In vitro experiments demonstrated that low temperature and TRPA1 agonists induced calcium influx, which was blocked by a TRPA1 inhibitor. TRPA1 expression exhibited post-prandial increases and was downregulated by fasting. TRPA1 activation dose-dependently inhibited food intake, while its inhibition restored feeding suppressed by low temperature. TRPA1 activation downregulated orexigenic factors and upregulated anorexigenic factors through Ca 2+ /calmodulin-dependent pathways. These findings suggest that TRPA1 plays a crucial role in sensing low temperatures and regulating feeding behavior in tilapia., Competing Interests: Declaration of competing interest No conflicts of interest, financial or otherwise, are declared by the authors., (Copyright © 2024 Elsevier B.V. All rights reserved.)

Hexaflumuron (HEX) insecticide is widely used in agriculture practices to fight crop insects. The toxicological effect of HEX on Nile tilapia (Oreochromis niloticus) was investigated in this study. Two hundred and forty fish (35.50 ± 1.45 g) were divided into six groups in four replicates (40 fish/group; 10 fish/replicate) and were exposed to six distinct HEX concentrations (0, 2, 4, 6, 8, and 10 mg L -1 ) for 96-h. The 96-h lethal concentration 50 (96-h LC 50 ) of HEX was calculated to be 7.19 mg L -1 . The fish exhibited reduced surface and middle swimming, aggressiveness, and tail-spreading behaviors with increasing bottom swimming and resting patterns after HEX exposure. HEX exposure resulted in body bleeding and fin rot. The erythrogram (red blood cell count, hemoglobin, and packed cell volume %) was significantly reduced with increased mean corpuscular volume by HEX exposure. HEX exposure decreased the white blood cells (WBCs) and differential WBC counts. Acute HEX exposure raised 8-hydroxy-2-deoxyguanosine level while lowering brain acetylcholine esterase activity. HEX exposure caused hepato-renal dysfunction and increased stress-related parameters (glucose and cortisol). Exposure to HEX reduced the immune responses (lysozyme, nitric oxide, immunoglobulin M, and complement 3). A substantial decrease in the antioxidant variables (reduced glutathione content and catalase) with increasing the malondialdehyde was noted by HEX exposure. Moreover, histopathological changes resulted from HEX exposure in the gills, liver, kidney, and spleen. These results indicate that HEX exposure induced behavioral changes, hepato-renal dysfunction, and immune-antioxidant disruption, indicating a possible physiological disruption in O. niloticus., (© 2024. The Author(s), under exclusive licence to Springer Nature B.V.)

In this study, we described immediate/acute reactions to stress-related chemical cues (SC - Stress Cue) in fish. Specifically, we evaluated the effects of SC on ventilation rate (VR) and feeding behavior in Nile tilapia ( Oreochromis niloticus ), a highly relevant species for world aquaculture, therefore, to understand the diversity of stressful contexts and stress responses in this species have important practical applications (stress reduction). Stress cue was obtained from conspecifics exposed to a handling stressor. Stress was confirmed by measuring plasma cortisol levels. The responses to SC were contrasted to chemical control cues: a cue originated from non-stressed conspecifics and pure water (vehicle control). We observed that Nile tilapia exposed to SC had an increase in VR, but without effects on feeding behavior (feeding latency and ingestion). Thus, the SC is a stressor that induces readily stress response (VR increase), suggesting sympathetic activation, but did not change feeding performance. In practical terms, it is positive because although social propagation of stress via SC elicits a stress response, it did not harm appetite.

Innate social behaviors like aggression are modulated by sex steroid hormones such as androgens and estrogens. However, we know little about how the same hormone regulates similar behaviors in both sexes. We investigated the role of androgenic signaling in the regulation of aggression in Astatotilapia burtoni, a social fish in which males and females perform similar aggressive behaviors. We used androgen receptor (AR) α knockout (KO) animals for this study since this gene was recently shown to be required for male-typical aggression and mating. Surprisingly, ARα KO females did not show deficits in aggression. We also determined that females lacking the other AR, ARβ, showed normal levels of aggression. Blocking both ARs pharmacologically confirmed that neither AR is necessary for aggression in females. However, ARα KO males showed clear deficits in attacks. Thus, in A. burtoni there appears to be a sexual dimorphism in the role of ARα in the control of aggression., Competing Interests: Declaration of competing interest None., (Copyright © 2024 Elsevier B.V. All rights reserved.)

Endocrine synchronization is a biological process often associated with social bonding. The mechanisms that mediate this process have been well studied in many vertebrate clades with evolved complex social behaviors. However, studies focusing on such processes in the less neurologically complex teleost clade are surprisingly lacking. In this study, we investigated the hypothesis that mated pairs of convict cichlids (Amatitlania nigrofasciata) perform cortisol synchronization and that the disruption of this might accompany pair-bond instability. Mated pairs were subjected to both behavioral and non-invasive waterborne hormonal assays to better understand the biological complexity of endocrine synchrony and its role in pair-bonding. Baseline cortisol assays indicated a positive correlation between male and female cortisol levels. Individuals that were subjected to a prolonged separation from their mate exhibited a negative correlation in cortisol synchrony after being reunited with their mate. Cortisol synchrony was disrupted, but pairs did not show a significant variance of intrapair aggression after initial pair reunion. However, more than half of the pairs that received the stressor exhibited significantly higher levels of intrapair aggression than their time matched controls approximately 1-7 days following this reunion, indicating pair-dissolution. Concurrently, pairs who underwent the stressor but maintained their bonds did not display an increase in intrapair aggression and also re-synchronized their cortisol levels. Not only does this study provide crucial insights in regard to the role of cortisol synchrony in serially monogamous systems, but it also suggests that the mechanisms that mediate the synchronization of endocrine through the formation of social bonds are more evolutionarily conserved than originally thought., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Inc. All rights reserved.)

The daily variations of temperature are one of the main synchronizers of the circadian rhythms. In addition, water temperature influences the embryonic and larval development of fish and directly affects their metabolic processes. The application of thermocycles to fish larvae has been reported to improve growth and the maturation of the digestive system, but their effects on metabolism are poorly understood. The aim of the present study was to evaluate the effect of two different temperature regimes, cycling versus constant, on the daily rhythms of metabolic factors of Nile tilapia (Oreochromis niloticus) larvae. For this purpose, fertilized eggs were divided into two groups: one reared in a 31 °C:25 °C day:night thermocycle (TCY) and another group maintained in a constant 28 °C temperature (CTE). The photoperiod was set to a 12:12 h light/dark cycle. Samples were collected every 4 h during a 24-h cycle on days 4, 8 and 13 post fertilization (dpf). The expression levels of alanine aminotransferase (alt), aspartate aminotransferase (ast), malic enzyme, glucose-6-phosphate dehydrogenase (g6pd), phosphofructokinase (pfk) and pyruvate kinase (pk) were analyzed by qPCR. Results showed that, in 13 dpf animals, most of the genes analyzed (alt, ast, malic, g6pd and pfk) showed daily rhythms in TCY, but not in the group kept at constant temperature, with most acrophases detected during the feeding period. An increase in nutrient metabolism around feeding time can improve food utilization and thus increase larval performance. Therefore, the use of thermocycles is recommended for tilapia larviculture., Competing Interests: Declaration of competing interest The authors whose names are listed immediately below certify that they have NO affi liations with or involvement in any organization or entity with any fi nancial interest (such as honoraria; educational grants; participation in speakers' bureaus; membership, employment, consultancies, stock ownership, or other equity interest; and expert testimony or patent-licensing arrangements), or non-fi nancial interest (such as personal or professional relationships, affi liations, knowledge or beliefs) in the subject matter or materials discussed in this manuscript., (Copyright © 2024 Elsevier Inc. All rights reserved.)

Climatic and geomorphological changes during the Quaternary period impacted global patterns of speciation and diversification across a wide range of taxa, but few studies have examined these effects on African riverine fish. The lower Congo River is an excellent natural laboratory for understanding complex speciation and population diversification processes, as it is hydrologically extremely dynamic and recognized as a continental hotspot of diversity harboring many narrowly endemic species. A previous study using genome-wide SNP data highlighted the importance of dynamic hydrological regimes to the diversification and speciation in lower Congo River cichlids. However, historical climate and hydrological changes (e.g., reduced river discharge during extended dry periods) have likely also influenced ichthyofaunal diversification processes in this system. The lower Congo River offers a unique opportunity to study climate-driven changes in river discharge, given the massive volume of water from the entire Congo basin flowing through this short stretch of the river. Here, we, for the first time, investigate the impacts of paleoclimatic factors on ichthyofaunal diversification in this system by inferring divergence times and modeling patterns of gene flow in four endemic lamprologine cichlids, including the blind cichlid, Lamprologus lethops. Our results suggest that Quaternary climate changes associated with river discharge fluctuations may have impacted the diversification of species along the system and the emergence of cryptophthalmic phenotype in some endemic species. Our study, using reduced representation sequencing (2RADseq), indicates that the lower Congo River lamprologines emerged during the Early-Middle Pleistocene transition, characterized as one of the earth's major climatic transformation periods. Modeling results suggest that gene flow across populations and between species was not constant but occurred in temporally constrained pulses. We show that these results correlate with glacial-interglacial fluctuations. The current hyper-diverse fish assemblages of the lower Congo River riverscape likely reflect the synergistic effects of multiple drivers fueling complex evolutionary processes through time., (© The Author(s) 2024. Published by Oxford University Press on behalf of the Society for Integrative and Comparative Biology.)

Reproductive behaviors differ across species, but the mechanisms that control variation in mating and parental care systems remain unclear. In many animal species, pheromones guide mating and parental care. However, it is not well understood how vertebrate pheromone signaling evolution can lead to new reproductive behavior strategies. In fishes, prostaglandin F 2α (PGF 2α ) drives mating and reproductive pheromone signaling in fertile females, but this pheromonal activity appears restricted to specific lineages, and it remains unknown how a female fertility pheromone is sensed for most fish species. Here, we utilize single-cell transcriptomics and CRISPR gene editing in a cichlid fish model to identify and test the roles of key genes involved in olfactory sensing of reproductive cues. We find that a pheromone receptor, Or113a, detects fertile cichlid females and thereby promotes male attraction and mating behavior, sensing a ligand other than PGF 2α . Furthermore, while cichlid fishes exhibit extensive parental care, for most species, care is provided solely by females. We find that males initiate mouthbrooding parental care if they have disrupted signaling in ciliated sensory neurons due to cnga2b mutation or if or113a is inactivated. Together, these results show that distinct mechanisms of pheromonal signaling drive reproductive behaviors across taxa. Additionally, these findings indicate that a single pheromone receptor has gained a novel role in behavior regulation, driving avoidance of paternal care among haplochromine cichlid fishes. Lastly, a sexually dimorphic, evolutionarily derived parental behavior is controlled by central circuits present in both sexes, while olfactory signals gate this behavior in a sex-specific manner., Competing Interests: Declaration of interests The authors declare no competing interests., (Copyright © 2024 Elsevier Inc. All rights reserved.)

Background: Oreochromis niloticus has great economic value and potential for farming and development. Transportation of fish was done for breeding or trading purpose and it is a challenging aspect of aquaculture. This study aimed to investigate the effect of transportation in freshwater and brackish water on the resistance of O. niloticus as well as transportation stress mitigation effect of NaCl. Four equal groups were used; each of 50 fish, the 1st group served as the control (P 1), while the 2nd group (PT 2) was transported in water without salt, the 3rd (PT 3) and 4th (PT 4) groups were transported in water containing 5 gL - 1 and 10 gL - 1 salt respectively. PT 2, PT 3 and PT 4 were transported for 5 h without any rest or sedative drugs., Results: The serum cortisol of O. niloticus significantly increased at 0 h and then decreased at 12 and 24 h post transportation in the PT 2 group and non-significantly increased at all point times in the PT 3 and PT 4 groups comparing to P 1 group. Mucin2 gene (MUC2) expression was non-significantly up regulated in the PT 2 group and down regulated in the PT 3 and PT 4 groups at 0 h comparing with P 1 group, but at 12 and 24 h it was significantly up regulated in the PT 2, PT 3 and PT 4 groups. The β Defensin-1 (β D1) and 2 (β D2) genes expression was non-significantly down-regulated in the PT 2 group and significantly up regulated in the PT 3 and PT 4 groups at 0 h., while at 12 and 24 h was significantly down regulated in the PT 2 group and non-significantly down regulated in the PT 3 and PT 4 groups, it significantly down regulated in the PT 2 and PT 3 group and non-significantly down regulated in the PT 4 group at 24 h. Non-significant up regulation in interleukin - 1β (IL-1β) gene expression was reported in the PT 2 group and non-significant down regulation in the PT 3 and PT 4 groups at 0 h. However, significant up regulation was recorded in the PT 2, PT 3 and PT 4 groups at 12 and 24 h. The Tumor necrosis factor-alpha (TNF-α) gene expression was non-significantly up regulated in the PT 2 group and non-significantly down regulated in the PT 3 and PT 4 groups at 0 h. However, it was significantly up regulated in the PT 2, PT 3 and PT 4 groups at 12 and 24 h., Conclusion: The results of this study confirmed the stressful effect of transportation on O. niloticus as well as the transportation stress mitigation effect of NaCl., (© 2024. The Author(s).)

AbstractAdaptive radiations highlight the mechanisms by which species and traits diversify and the extent to which these patterns are predictable. We used 1,110 high-speed videos of suction feeding to study functional and morphological diversification in 300 cichlid species from three African Great Lake radiations of varying ages (Victoria, Malawi, and Tanganyika) and an older, spatially dispersed continental radiation in the Neotropics. Among African radiations, standing diversity was reflective of time. Morphological and functional variance in Lake Victoria, the youngest radiation, was a subset of that within Lake Malawi, which itself was nested within the older Tanganyikan radiation. However, functional diversity in Neotropical cichlids was often lower than that in Lake Tanganyika, despite being much older. These two radiations broadly overlapped, but each diversified into novel trait spaces not found in the youngest lake radiations. Evolutionary rates across radiations were inversely related to age, suggesting extremely rapid trait evolution at early stages, particularly in lake radiations. Despite this support for early bursts, other patterns of trait diversity were inconsistent with expectations of adaptive radiations. This work suggests that cichlid functional evolution has played out in strikingly similar fashion in different radiations, with contingencies eventually resulting in lineage-specific novelties.

Two examples of vertebrates that feed young with mucus. Left: A female cichlid fish Symphysodon aequifasciatus; Right: A female caecilian Siphonops annulatus., (© 2024 International Society of Zoological Sciences, Institute of Zoology/Chinese Academy of Sciences and John Wiley & Sons Australia, Ltd.)

Fishmeal substitution with sustainable feed sources is highly essential towards sustainable production. This study aimed to investigate the effects of substituting fishmeal (FM) with Daphnia magna biomass meal (DBM) or zooplankton biomass meal (ZBM) on growth performance, liver and intestinal histology, gut bacterial abundance and stress tolerance of Nile tilapia, Oreochromis niloticus, fry. Nile tilapia fry (0.23 ± 0.04 g) were randomly assigned to five groups of three replicates. The control diet comprised 300 g/kg FM, and the FM was substituted with DBM or ZBM at levels of 25% and 50% (DBM-25, DBM-50, ZBM-25 and ZBM-50 respectively) in the other experimental diets. The experiment lasted 56 days in 1.5 m 3 concrete tanks. The results revealed that weight gain and feed conversion ratio (FCR) significantly (p ≤ 0.035 and 0.025 respectively) improved with a polynomial response with a peak at 25% ZBM and a linear increase with DBM up to 50% of FM. Histometric indices of the distal intestine showed improvements (p ≤ 0.001) in villus height, villus width, crypt depth and muscle thickness of fish fed DBM or ZBM compared to the control. In the meantime, there were no histological abnormalities in the liver sections. The replacement of FM with DBM or ZBM could modulated gut bacterial abundance, including total bacterial count, Escherichia coli, Bacillus subtilis, and Lactobacillus sp. The fish-fed DBM or ZBM-containing diets had higher (p ≤ 0.05) tolerances to salinity stress than the control group. In conclusion, DBM or ZBM could replace FM up to 50% and 25%, respectively with improved fish growth performance, FCR, gut histology and tolerance to salinity stress., (© 2024 Wiley‐VCH GmbH. Published by John Wiley & Sons Ltd.)

Probiotics are becoming increasingly popular as eco-friendly alternatives in aquaculture. However, there is limited research on their impacts on the reproductive efficiency of Red Tilapia (Oreochromis niloticus x O. mossambicus) broodstock. Therefore, this experiment aimed to explore the combined effects of selective probiotics Bacillus subtilis and B. licheniformis (BSL; 1:1) added to water on blood hematology, serum metabolites, gonadal histology, reproductive performance, and reproductive associated genes in Red Tilapia broodstock. Tilapia broodfish weighing 140-160 g were stocked in four treatment groups: control (T0), and the other three groups were added different levels of BSL to the water as follows: T1 (0.01 g/m 3 ), T2 (0.02 g/m 3 ), and T3 (0.03 g/m 3 ), respectively. Results indicate that BSL administration significantly improved RBCs, hemoglobin, hematocrit, MCH, and MCHC, with the highest improvement seen in the T3 group (P < 0.05). BSL added to the fish water significantly enhanced serum protein fractions (total protein, albumin, and globulins), while AST, ALT, ALP, creatinine, uric acid, and glucose were significantly diminished in a dose-dependent way (P < 0.05). Adding 0.02-0.03 g/ m 3 of BSL resulted in higher antioxidant status (superoxide dismutase and catalase) compared to other groups (P < 0.05). Testosterone levels were higher in T3 than in other groups (P < 0.05). All female hormones (LH, FSH, estradiol, and progesterone) were substantially augmented by the addition of BSL. Additionally, the BSL groups exhibited higher GSI, HSI, VSI (male only), egg diameter (mm), mean number of fry/fish, and mean fry weight (g) compared to the control group (P < 0.05). Expression of reproductive-associated genes (vasa, nanos1a, nanos2, dnd1, pum1, AMH, and vtg) were significantly up-regulated in the gonads of fish in the 0.03 g/m 3 treatment. The histological gonadal structure exhibited that BSL improved gonad maturation in both genders of Tilapia fish. Overall, adding a mixture of B. subtilis and B. licheniformis (0.03 g/m 3 water) can accelerate reproductive performance in Red Tilapia through up-regulation of reproductive genes and enhance the health profile., (© 2024. The Author(s).)

Optimizing fish performance depends on several factors, with dietary protein levels and rearing temperature playing important roles. In this study, Nile tilapia fingerlings (Oreochromis niloticus) weighing an average of 20.00 ± 1.26 g were divided into nine groups (in three replicates). Each group was subjected to different water temperatures (26 °C, 28 °C, and 30 °C) and received one of three dietary protein levels (20%, 25%, and 30%) for two months. Our findings indicate that higher temperatures, particularly at 30 °C, increased water electrical conductivity and total dissolved salts, especially noticeable in fish fed 25% or 30% crude protein (CP). Lower total ammonia nitrogen levels were observed at 28 °C with 25% CP, 30 °C with 30% CP, and 26 °C with 30% CP. Hepatic growth hormone receptor 1 and insulin-like growth factor 1 expression gradually rose with higher dietary CP percentages in fish at 26 °C but declined in those at 30 °C, albeit remaining higher than in the 28 °C groups with 25% CP. Fish at 28 °C showed the best final body weights and growth performance when fed 20% or 25% CP, with no significant difference between these groups. Hepatic leptin expression did not differ significantly among groups, but hepatic fatty acid binding protein expression notably increased in fish fed 30% CP at both 26 °C and 30 °C compared to those at 28 °C with 25% CP. Within the same temperature group, fish fed 30% CP exhibited higher globulin levels, particularly thriving at 28 °C or 30 °C. Hepatic mucin-like protein expression significantly increased across all groups, especially in fish at 30 °C with 30% CP compared to those at 28 °C with 25% CP. Hepatic lysozyme expression also increased notably in fish at 30 °C with 30% CP. Notable changes in superoxide dismutase, catalase, and glutathione peroxidase expression were observed, with the highest serum superoxide dismutase and catalase activities recorded in fish at 30 °C with 25% CP. Overall, dietary protein levels of 25% and 30%, combined with temperatures of 28 °C and 30 °C, yielded favorable outcomes, particularly favoring 28 °C with 25% protein., (© 2024. The Author(s).)

The study introduced and evaluated learning paradigms for Maylandia callainos cichlids using a modified version of the rodent T-maze, filled with tank water (the "sunken" modification). Both male and female fish underwent training in two distinct conditioning paradigms. Firstly, simple operant conditioning involved placing a food reward in either the right or left compartment. Cichlids demonstrated the ability to purposefully find the bait within 6 days of training, with a persistent place preference lasting up to 6 days. Additionally, the learning dynamics varied with sex: female cichlids exhibited reduction in latency to visit the target compartment and consume the bait, along with a decrease in the number of errors 3 and 4 days earlier than males, respectively. Secondly, visually-cued operant conditioning was conducted, with a food reward exclusively placed in the yellow compartment, randomly positioned on the left or right side of the maze during each training session. Visual learning persisted for 10 days until reaction time improvement plateaued. Color preference disappeared after 4 consecutive check-ups, with no sex-related interference. For further validation of visually-cued operant conditioning paradigm, drugs MK-801 (dizocilpine) and caffeine, known to affect performance in learning tasks, were administered intraperitoneally. Chronic MK-801 (0.17 mg/kg) impaired maze learning, resulting in no color preference development. Conversely, caffeine administration enhanced test performance, increasing precision in fish. This developed paradigm offers a viable approach for studying learning and memory and presents an effective alternative to rodent-based drug screening tools, exhibiting good face and predictive validity., Competing Interests: Declaration of Competing Interest At the time of completing the experiments and writing the manuscript, the team of authors was employed by Lactocore, Inc. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript; or in the decision to publish the results., (Copyright © 2024 Elsevier B.V. All rights reserved.)

AbstractPhenotypic macroevolutionary studies provide insight into how ecological processes shape biodiversity. However, the complexity of phenotype-ecology relationships underscores the importance of also validating phenotype-based ecological inference with direct evidence of resource use. Unfortunately, macroevolutionary-scale ecological studies are often hindered by the challenges of acquiring taxonomically and spatially representative ecological data for large and widely distributed clades. The South American cichlid fish tribe Geophagini represents a continentally distributed radiation whose early locomotor morphological divergence suggests habitat as one ecological correlate of diversification, but an association between locomotor traits and habitat preference has not been corroborated. Field notes accumulated over decades of collecting across South America provide firsthand environmental records that can be mined for habitat data in support of macroevolutionary ecological research. In this study, we applied a newly developed method to transform descriptive field note information into quantitative habitat data and used it to assess habitat preference and its relationship to locomotor morphology in Geophagini. Field note-derived data shed light on geophagine habitat use patterns and reinforced habitat as an ecological correlate of locomotor morphological diversity. Our work emphasizes the rich data potential of museum collections, including often-overlooked material such as field notes, for evolutionary and ecological research.

Classical assessments of new fish feeds are anthropocentric, focusing mainly on growth. Although this methodology is accurate, it does not consider the fish' perspective. This study aimed to investigate the behavioural responses and feed preferences of Nile tilapia (Oreochromis niloticus) and gilthead seabream (Sparus aurata) through a self-selection trial using self-feeders. Both species were offered three feeds: a control (PD) commercial-like feed and two diets (ORG1 and ORG2) formulated with different inclusions of alternative ingredients to address some of the current environmental concerns and/or ethical issues often associated with commercial formulations. Three groups of tilapia with an average weight of 163.0 g ± 4.3 g (mean ± SD) and four groups of seabreams with 174.7 g ± 27.0 g were tested. Tilapia exhibited a preference for ORG2 (46.5%), influenced by the sensory properties of the feed and post-ingestion signals. Seabream did not show a preference for any feed. These findings highlight the effectiveness of self-selection experiments in allowing fish to express their feeding behaviour and preferences. Therefore, this approach should be considered in the initial screening and design of new aquaculture feeds and ingredients., (© 2024. The Author(s).)

This study aims to evaluate the effects of substituting soybean meal with fermented rapeseed meal (FRM) on growth, antioxidant capacity, and liver and intestinal health of the genetically improved farmed tilapia (GIFT, Oreochromis niloticus). A total of 450 tilapia (7.22 ± 0.15 g) were fed with five experimental diets, including a basal diet containing 40% soybean meal (CP0), which was subsequently replaced by 25% (CP25), 50% (CP50), 75% (CP75), and 100% (CP100) FRM in a recirculated aquiculture system for 9 weeks (30 fish per tank in triplicates). The results showed that the weight gain, specific growth rate, feed intake, feed efficiency, hepatosomatic index, and viscerosomatic index of fish in both CP75 and CP100 groups were significantly lower than those in CP0 group (P < 0.05). The fish in CP100 group had the lower content of muscle crude protein while the higher level of muscle crude lipid (P < 0.05). Activities of serum aspartate aminotransferase, alanine aminotransferase along with total triglyceride in CP100 group were significantly higher than those in CP0 group (P < 0.05). There were no significant differences in the contents of liver protease, amylase, and lipase among five groups (P > 0.05). The activities of liver total antioxidant capacity and superoxide dismutase exhibited the increased tendency with the increase of FRM replacement levels from 25 to 50% (P < 0.05), while then significantly decreased from 75 to 100% (P < 0.05). Histological morphology indicated that the fish in between CP75 and CP100 groups had poor liver and intestine health. Intestinal microbial diversity analysis showed that the relative abundance of Cetobacterium and Alcaligenaceae in both CP75 and CP100 groups were lower than that in other three groups. In conclusion, the maximum replacement level of soybean meal with FRM in the diet was determined to be 50% without compromising the growth performance, antioxidant status, and liver and intestinal health of tilapia under the current experimental conditions. The observed decrease in food intake and subsequent retarded growth performance in the CP75 and CP100 groups can be attributed directly to a reduction in feed palatability caused by FRM., (© 2024. The Author(s), under exclusive licence to Springer Nature B.V.)

In fish, thermal and hypoxia tolerances may be functionally related, as suggested by the oxygen- and capacity-limited thermal tolerance (OCLTT) concept, which explains performance failure at high temperatures due to limitations in oxygen delivery. In this study the interrelatedness of hyperthermia and hypoxia tolerances in the Nile tilapia (Oreochromis niloticus), and their links to cardiorespiratory traits were examined. Different groups of O. niloticus (n = 51) were subjected to hypoxia and hyperthermia challenges and the O 2 tension for aquatic surface respiration (ASR pO 2 ) and critical thermal maximum (CTmax) were assessed as measurement endpoints. Gill filament length, total filament number, ventricle mass, length and width were also measured. Tolerance to hypoxia, as evidenced by ASR pO 2 thresholds of the individual fish, was highly variable and varied between 0.26 and 3.39 kPa. ASR events increased more profoundly as O 2 tensions decreased below 2 kPa. The CTmax values recorded for the O. niloticus individuals ranged from 43.1 to 44.8 °C (Mean: 44.2 ± 0.4 °C). Remarkably, there was a highly significant correlation between ASR pO 2 and CTmax in O. niloticus (r = -0.76, p < 0.0001) with ASR pO 2 increasing linearly with decreasing CTmax. There were, however, no discernible relationships between the measured cardiorespiratory properties and hypoxia or hyperthermia tolerances. The strong relationship between hypoxia and hyperthermia tolerances in this study may be related to the ability of the cardiorespiratory system to provide oxygen to respiring tissues under thermal stress, and thus provides some support for the OCLTT concept in this species, at least at the level of the entire organism., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Inc. All rights reserved.)

The expression of sexually selected traits, such as ornaments or body coloration, is often influenced by environmental conditions. While such phenotypic plasticity is often thought to precede evolutionary change, plasticity itself can also be a target of selection. However, the selective forces supporting the evolution and persistence of plasticity in sexual traits are often unclear. Using the cichlid fish Astatotilapia burtoni , we show that variation in the level of mate competition may promote plasticity in body coloration. In this species, males can change between yellow and blue colour. We found that experimentally increased competition over mating territories led to a higher proportion of males expressing the yellow phenotype. The expression of yellow coloration was found to be beneficial because yellow males won more staged dyadic contests and exhibited a lower level of oxidative stress than blue males. However, females were more likely to spawn with blue males in mate choice experiments, suggesting that expression of blue coloration is sexually more attractive. The ability to adjust colour phenotype according to the local competitive environment could therefore promote the persistence of plasticity in coloration.

Nile Tilapia (Oreochromis niloticus) management procedures are directly linked to the final quality of the product. The aim of this study was to evaluate the effect of pre-slaughter density and different stunning methods on biochemical, respiratory and muscle injury parameters associated with quality and sensory characteristics of Nile tilapia fillets. Fish with an average weight of 762±105 g were used, first collected called the control group. The experiment was conducted in a 2 × 2 factorial scheme, with two densities (50 and 300 kg of live weight m-3) and two stunning methods thus totaling four treatments, with 15 repetitions per treatment totaling 75 fish sampled. Blood gas analysis, evaluation of biochemical parameters, analysis of meat quality and sensory analysis were carried out. For blood gas, biochemical and enzymatic parameters, the highest values were obtained for the density of 300 kg m-3 and asphyxia method: partial pressures of CO2; glucose and lactate, the highest values presented were 268.98 and 11.33 mg dL-1 respectively. As well as enzymatic activities, Creatinine kinase (CPK); Creatinine kinase isoenzyme (CKMB) showed higher values (768.93 and 1078.98 mg dL-1 respectively) in the higher density and asphyxia method. Conversely, when evaluating the quality parameters, the highest values were observed for lower density and thermonarcosis. High depuration density (300 kg m-3), combined with the asphyxiation stunning method, promotes changes in respiratory dynamics and provides greater stress, less firm fillet texture and greater weight loss due to cooking, as well as changes in creatine kinase (CK) and its CK-MB isoenzyme, demonstrating greater muscle damage. On the other hand, the density of 50 kg m-3 during pre-slaughter, combined with the method of stunning by thermonarcosis, provide a longer period of permanence in pre rigor mortis, which will result in fillets with a better sensory profile., Competing Interests: The authors have declared that no competing interests exist., (Copyright: © 2024 Prestes dos Santos et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.)

Background: The inappropriate use of pesticides including fungicides creates severe biological hazards that can endanger fish health and impede sustainable aquaculture., Objective: This study investigated the negative impacts of metiram (MET), a fungicide on the health status of Nile tilapia (Oreochromis niloticus) for a 96-hour duration as an acute exposure in a static renewal system., Methods: Three hundred fish (average body weight: 37.50 ± 0.22 g) were assigned into six groups (50 fish/group) with five replicates (10 fish/replicate). Fish were exposed to various six concentrations (0, 1.5, 3, 4.5, 6, and 7.5 mg/L) of MET as a water exposure to for 96-hour without water exchange. The fish's behavior, clinical signs, and mortalities were documented every day of the exposure period. Additionally, MET's impact on blood profile, stress biomarkers, hepato-renal functions, immune-antioxidant status, and brain biomarker were closely monitored., Results: The lethal concentration (LC 50 ) of MET estimated using Finney's probit technique was 3.77 mg/L. The fish's behavior was severely impacted by acute MET exposure, as clear by an increase in surfacing, loss of equilibrium, unusual swimming, laterality, abnormal movement, and a decline in aggressive behaviors. The survivability and hematological indices (white and red blood cell count, differential white blood cell count, hematocrit value, and hemoglobin) were significantly reduced in a concentration-dependent manner following MET exposure. Acute exposure to MET (1.5-7.5 mg/L) incrementally increased stress biomarkers (nor-epinephrine, cortisol, and glucose), lipid peroxides (malondialdehyde), and brain oxidative DNA damage biomarker (8-hydroxy-2-deoxyguanosine). A hepato-renal dysfunction by MET exposure (4.5-7.5 mg/L) was evidenced by the significant increase in the alanine and aspartate aminotransferases and creatinine values. Moreover, a substantial decline in the immune parameters (lysozyme, complement 3, serum bactericidal activity, and antiprotease activity) and antioxidant variables (total antioxidant capacity, superoxide dismutase, and glutathione peroxidase) resulted from acute MET exposure., Conclusion: According to these findings, the 96-hour LC 50 of MET in Nile tilapia was 3.77 mg/L. MET exposure triggered toxicity in Nile tilapia, as seen by alterations in fish neuro-behaviors, immune-antioxidant status, hepato-renal functioning, and signifying physiological disturbances. This study emphasizes the potential ecological dangers provoked by MET as an environmental contaminant to aquatic systems. However, the long-term MET exposure is still needed to be investigated., (© 2024. The Author(s).)

Social interactions can sometimes be a source of stress, but social companions can also ameliorate and buffer against stress. Stress and metabolism are closely linked, but the degree to which social companions modulate metabolic responses during stressful situations-and whether such effects differ depending on social rank-is poorly understood. To investigate this question, we studied Neolamprologus pulcher , a group-living cichlid fish endemic to Lake Tanganyika and measured the metabolic responses of dominant and subordinate individuals when they were either visible or concealed from one another. When individuals could see each other, subordinates had lower maximum metabolic rates and tended to take longer to recover following an exhaustive chase compared with dominants. In contrast, metabolic responses of dominants and subordinates did not differ when individuals could not see one another. These findings suggest that the presence of a dominant individual has negative metabolic consequences for subordinates, even in stable social groups with strong prosocial relationships.

A key challenge in animal behavior is disentangling the social stimuli that drive conspecific behaviors. For some species, like teleost fish, putative sexual signaling cues are inextricably linked to others, making it difficult to parse the precise roles distinct signals play in driving conspecific behaviors. In the African cichlid Astatotilapia burtoni, males are either dominant or subordinate, wherein bright coloration, territoriality, and courtship behavior inextricably correlate positively with rank. Here, we leveraged androgen receptor (AR) mutant male A. burtoni that lack dominance-typical coloration but not behavior to isolate the role of male coloration in driving female mating behaviors in this species. We found in independent behavioral assays that females behave aggressively towards AR mutant but not WT males, yet still mated with both types of males. Females showed enhanced activation of esr2b + cells in the hypothalamus when housed with either mutant or WT males and this activation scaled with spawning activities. Therefore, there is not a simple relationship between male coloration and female mating behaviors in A. burtoni, suggesting independent sensory mechanisms converge on hypothalamic esr2b cells to coordinate behavioral output., Competing Interests: Declaration of competing interest The authors declare no competing or financial interests., (Copyright © 2024 Elsevier Inc. All rights reserved.)

Background: Using anaesthetics is an important application in aquaculture especially where the fish transportation, vaccination, grading, sorting activities and many other handling operations have been conducted during the different stages of production periods in the farms or hatcheries., Objectives: This study aimed to evaluate the efficacy of oregano essential oil (OO) as an anaesthetic for Nile tilapia and to determine the optimal concentration and post-application stress effects compared to clove oil (CO)., Methods: Nile tilapia juveniles were exposed to different concentrations of OO (20-40-60-80-100 mg L -1 ) and CO (50 mg L -1 ) for different time periods to determine the optimal concentration and exposure time. After the effective concentration of OO was determined, in the second experiment, stress parameters (glucose, plasma cortisol) were analysed after 0, 2, 6, 12 and 24 h of application. The results compared to the control group and CO results., Results: The study found that OO which has carvacrol compound higher than 78% was an efficient anaesthetic for Nile tilapia, and the effective concentration was found to be 60 mg L -1 . No significant differences were found between opercular beats in any concentration of OO and CO. Basal glucose level in blood without anaesthesia application and recorded at 39.33 mg dL -1 and significantly lower than OO and CO at first two sampling points, 0 and 2 h (p < 0.05). According to plasma cortisol level results, although CO experimental group showed secondary stress response at 12 h (17.91 ± 4.21 ng mL -1 ), OO and CO group cortisol levels decreased at 24 h after anaesthesia application 7.13 ± 0.14and 7.01 ± 0.54 ng mL -1 , respectively, below the control group cortisol concentration (12.28 ± 1.81 ng mL -1 )., Conclusions: These findings have important implications for the aquaculture industry as the use of OO as an anaesthetic could reduce the stress and mortality associated with traditional anaesthetics. Further research is needed to evaluate the efficacy of OO as an anaesthetic agent for other fish species and to determine the optimal concentration and exposure time for different species., (© 2024 The Author(s). Veterinary Medicine and Science published by John Wiley & Sons Ltd.)

We used computer simulations of growth, mating and death of cephalopods and fishes to explore the effect of different life-history strategies on the relative prevalence of alternative male mating strategies. Specifically, we investigated the consequences of single or multiple matings per lifetime, mating strategy switching, cannibalism, resource stochasticity, and altruism towards relatives. We found that a combination of single (semelparous) matings, cannibalism and an absence of mating strategy changes in one lifetime led to a more strictly partitioned parameter space, with a reduced region where the two mating strategies co-exist in similar numbers. Explicitly including Hamilton's rule in simulations of the social system of a Cichlid led to an increase of dominant males, at the expense of both sneakers and dwarf males ("super-sneakers"). Our predictions provide general bounds on the viable ratios of alternative male mating strategies with different life-histories, and under possibly rapidly changing ecological situations., (© 2024. The Author(s), under exclusive licence to the Society for Mathematical Biology.)

Water quality in land-based fish production can be controlled through either instantaneous water exchange or costly wastewater treatment followed by recirculation. Agricultural-aquaculture integration is an excellent alternative technique for reducing nutrient discharge levels, boosting profitability, and converting fish culture wastewater into valuable products. The current study employed a solar energy system to power two separate IMTA-aquaponics systems (Nutrient Film Technique, NFT, and Floating Raft Systems, FRS) for the cultivation of Nile tilapia, African catfish, thin-lipped grey mullet, freshwater crayfish, freshwater mussels, and a variety of vegetables. Tilapia and catfish were fed exclusively on diets under the IMTA system. All wastewater from tilapia and catfish ponds, both dissolved and solid, flows sequentially to ponds containing other cultivated species. The water then flows through the IMTA system's terminal point to the NFT and FRS systems before returning to the tilapia and catfish ponds, allowing complete control of the nutrient flow throughout this entire circular system. Two 147-day production cycles were concluded. The results from the second production cycle are reported. Total biomass gain for aquatic species in the IMTA system was 736.46 kg, compared to 145.49 kg in the tilapia and 271.01 kg in the catfish monoculture systems. The current IMTA system had a cumulative feed conversion ratio (FCR) of 0.90, while the FCRs for tilapia and catfish were 1.28 and 1.42, respectively. Nile tilapia and catfish consumed 571.90 kg of feed containing 25.70 kg of nitrogen (N) and 9.70 kg of phosphorus (P), reflecting, and gaining 11.41 and 3.93 kg of dietary N and P, representing 44.40 and 40.46% dietary N and P retention, respectively. In the IMTA system, the addition of mullet and prawn as detrivores aquatic animals improves dietary N and P utilization efficiency to 59.06 and 51.19%, respectively, while the addition of mussels as herbivore animals improves dietary N and P utilization efficiency to 65.61 and 54.67%, respectively. Finally, using FRS and NFT as hydroponic systems increased dietary N and P efficiency to 83.51% N and 96.82% P, respectively. This study shows that the IMTA-Aquaponic system, as a bio-integrated food production system, can convert the majority of fish-fed residues into valuable products suitable for desert, rural, and urban areas in impoverished and developing countries., (© 2024. The Author(s).)

This study evaluates the impact of dietary supplementation of the blue-green alga Arthrospira platensis NIOF17/003 nanoparticles (AN) on the growth performance, whole-body biochemical compositions, blood biochemistry, steroid hormonal, and fry production efficiency of Nile tilapia (Oreochromis niloticus) broodstock, during the spawning season. After a 21-day preparation period to equip the females and ensure that their ovaries were filled with eggs, mating between the mature females and males took place in a 3:1 ratio during a 14-day spawning cycle. A total of 384 tilapia broodstock 288 females and 96 males with an initial body weight of 450.53±0.75, were divided into four groups; AN0: a basal diet as a control group with no supplementation of Arthrospira platensis, and the other three groups (AN2, AN4, and AN6) were diets supplemented with nanoparticles of A. platensis at levels of 2, 4, and 6 g kg─1 diet, respectively. The results found that fish-fed group AN6 showed the highest significant differences in weight gain (WG), final weight (FW), feed conversion ratio (FCR), protein efficiency ratio (PER), and feed efficiency ratio (FER). Females fed the AN6 diet showed the highest significant fat content. Compared to the AN0 group, fish fed on the supplemented diets showed significant improvement (p < 0.05) in triglyceride, glucose, and aspartate aminotransferase (AST). A gradual increase in AN inclusion level resulted in a gradual increase in the concentrations of luteinizing hormone (LH), and follicle-stimulating hormone (FSH), testosterone, progesterone, and prolactin. The rates (%) of increase in fry production for females fed supplemented diets were 10.5, 18.6, and 32.2% for AN2, AN4, and AN6, respectively, compared to the control group. This work concluded that the inclusion levels of 6 g kg─1 of A. platensis nanoparticles in the diet of Nile tilapia broodstock significantly improved the growth performances, steroid hormone concentrations, and increased the fry production efficiency by 32.2%, respectively. These findings revealed that A. platensis nanoparticles resulted in a significantly enhanced female' reproductive productivity of Nile tilapia broodstock., Competing Interests: The authors have declared that no competing interests exist., (Copyright: © 2024 Mabrouk et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.)

In addition to an oral jaw, cichlids have a pharyngeal jaw, which is used for crushing and processing captured prey. The teeth and morphology of the pharyngeal jaw bones adapt to changes in prey in response to changes in the growing environment. This study aimed to explore the possible involvement of the peripheral nervous system in remodeling the cichlid pharyngeal jaw by examining the innervation of the inferior pharyngeal jaw in the Nile tilapia, Oreochromis niloticus. Vagal innervation was identified in the Nile tilapia inferior pharyngeal jaw. Double staining with tartrate-resistant acid phosphatase and immunostaining with the neuronal markers, protein gene product 9.5, and acetylated tubulin, revealed that osteoclasts, which play an important role in remodeling, were distributed in the vicinity of the nerves and were in apposition with the nerve terminals. This contact between peripheral nerves and osteoclasts suggests that the peripheral nervous system may play a role in remodeling the inferior pharyngeal jaw in cichlids., (© 2024 American Association for Anatomy.)

Activity patterns tend to be highly stereotyped and critical for executing many different behaviors including foraging, social interactions, and predator avoidance. Differences in the circadian timing of locomotor activity and rest periods can facilitate habitat partitioning and the exploitation of novel niches. As a consequence, closely related species often display highly divergent activity patterns, suggesting that shifts from diurnal to nocturnal behavior, or vice versa, are critical for survival. In Africa's Lake Malawi alone, there are over 500 species of cichlids, which inhabit diverse environments and exhibit extensive phenotypic variation. We have previously identified a substantial range in activity patterns across adult Lake Malawi cichlid species, from strongly diurnal to strongly nocturnal. In many species, including fishes, ecological pressures differ dramatically across life-history stages, raising the possibility that activity patterns may change over ontogeny. To determine if rest-activity patterns change across life stages, we compared the locomotor patterns of six Lake Malawi cichlid species. While total rest and activity did not change between early juvenile and adult stages, rest-activity patterns did, with juveniles displaying distinct activity rhythms that are more robust than adults. One distinct difference between juveniles and adults is the emergence of complex social behavior. To determine whether social context is required for activity rhythms, we next measured locomotor behavior in group-housed adult fish. We found that when normal social interactions were allowed, locomotor activity patterns were restored, supporting the notion that social interactions promote circadian regulation of activity in adult fish. These findings reveal a previously unidentified link between developmental stage and social interactions in the circadian timing of cichlid activity., (© 2023. The Author(s).)

Ammonia is a respiratory gas that is produced during the process of protein deamination. In the unionised form (NH 3 ), it readily crosses biological membranes and is highly toxic to fish. In the present study we examined the effects of unionized ammonia (UIA), on the resting oxygen consumption (MO 2 ), ventilation frequency (f V ), heart rate (HR) and heart rate variability (HRV) in Nile tilapia (Oreochromis niloticus). Fish were either exposed to progressively increasing UIA concentrations, up to 97 µM over a 5 h period, or to a constant UIA level of 7 µM over a 24 h period. For both treatment groups resting MO 2 , HR and f V were recorded as physiological variables. Relative to the control group, the fish groups exposed to the incremental UIA levels did not exhibit significant changes in their MO 2 , HR and f V at UIA concentrations of 4, 10, 35, or 61 µM compared to control fish. Exposure to 97 µM UIA, however, elicited abrupt and significant downregulations (p < 0.05) in all three responses, as MO 2 , HR and fv decreased by 25, 54 and 76 % respectively, compared to control measurements. Heart rate became increasingly irregular with increasing UIA concentrations, and heart rate variability was significantly increased at 61 and 97 µM UIA. Prolonged exposure elicited significant changes at exposure 7 µM UIA. Standard (SMR) and maximum metabolic rate (MMR) were significantly reduced, as was the corresponding f V and HR. It is evident from this study that Nile tilapia is tolerant to short term exposure to UIA up to 61 µM but experience a significant metabolic change under conditions of prolonged UIA exposures even at low concentrations., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 The Author(s). Published by Elsevier B.V. All rights reserved.)

The growth, immune response, and reproductive performance of broodstock of Nile tilapia (Oreochromis niloticus) under winter stress conditions were investigated the effects of supplementary diets with astaxanthin-enriched Paracoccus carotinifaciens. Throughout an eight-week period in the winter season, male and female tilapia were fed with diets containing different levels of P. carotinifaciens dietary supplementation: 0 g/kg (T1; control), 5 g/kg (T2), 10 g/kg (T3), and 20 g/kg (T4). Subsequently, a four-week mating system was implemented during the winter stress period. The results revealed that there were no significant differences observed in growth, hematological indices, and blood chemical profiles among all treatment groups for both male and female tilapia. However, a significant increase in cholesterol content was noted in both male and female tilapia fed with the T4 diet (p<0.05). The total carotenoid content in the muscle was evaluated, and significantly higher values were found in both male and female tilapia that fed T4 supplementation (p<0.05). Moreover, immunological parameters such as myeloperoxidase and antioxidant parameters in the liver including superoxide dismutase activity and catalase enzyme activity showed significant increases in tilapia fed with the T4 diet. The impact of P. carotinifaciens supplementation on broodstock tilapia indicated a significant increase in spermatozoa concentration in males and increased egg production in females after consumption of the T4 diet (p<0.05). Thus, this study highlighted that the presence of astaxanthin-enriched P. carotinifaciens in the diet of broodstock Nile tilapia can lead to the accumulation of carotenoids in their muscle tissue, improvement in antioxidant status, enhancement of immune function, and potential enhancement of reproductive capabilities, even under overwintering conditions., (© 2024. The Author(s), under exclusive licence to Springer Nature B.V.)

The neuropeptides arginine vasopressin (AVP) and oxytocin (OXT) are key regulators of social behaviour across vertebrates. However, much of our understanding of how these neuropeptide systems interact with social behaviour is centred around laboratory studies which fail to capture the social and physiological challenges of living in the wild. To evaluate relationships between these neuropeptide systems and social behaviour in the wild, we studied social groups of the cichlid fish Neolamprologus pulcher in Lake Tanganyika, Africa. We first used SCUBA to observe the behaviour of focal group members and then measured transcript abundance of key components of the AVP and OXT systems across different brain regions. While AVP is often associated with male-typical behaviours, we found that dominant females had higher expression of avp and its receptor (avpr1a2) in the preoptic area of the brain compared to either dominant males or subordinates of either sex. Dominant females also generally had the highest levels of leucyl-cystinyl aminopeptidase (lnpep)-which inactivates AVP and OXT-throughout the brain, potentially indicating greater overall activity (i.e., production, release, and turnover) of the AVP system in dominant females. Expression of OXT and its receptors did not differ across social ranks. However, dominant males that visited the brood chamber more often had lower preoptic expression of OXT receptor a (oxtra) suggesting a negative relationship between OXT signalling and parental care in males of this species. Overall, these results advance our understanding of the relationships between complex social behaviours and neuroendocrine systems under natural settings., Competing Interests: Declaration of competing interest The authors declare no competing interests., (Copyright © 2024 The Authors. Published by Elsevier Inc. All rights reserved.)

Background: Living in a social dominance hierarchy presents different benefits and challenges for dominant and subordinate males and females, which might in turn affect their cognitive needs. Despite the extensive research on social dominance in group-living species, there is still a knowledge gap regarding how social status impacts brain morphology and cognitive abilities., Methods: Here, we tested male and female dominants and subordinates of Neolamprologus pulcher, a social cichlid fish species with size-based hierarchy. We ran three executive cognitive function tests for cognitive flexibility (reversal learning test), self-control (detour test), and working memory (object permanence test), followed by brain and brain region size measurements., Results: Performance was not influenced by social status or sex. However, dominants exhibited a brain-body slope that was relatively steeper than that of subordinates. Furthermore, individual performance in reversal learning and detour tests correlated with brain morphology, with some trade-offs among major brain regions like telencephalon, cerebellum, and optic tectum., Conclusion: As individuals' brain growth strategies varied depending on social status without affecting executive functions, the different associated challenges might yield a potential effect on social cognition instead. Overall, the findings highlight the importance of studying the individual and not just species to understand better how the individual's ecology might shape its brain and cognition., (© 2024 The Authors. Brain and Behavior published by Wiley Periodicals LLC.)

Phenotypic plasticity is the ability of a single genotype to vary its phenotype in response to the environment. Plasticity of the skeletal system in response to mechanical input is widely studied, but the timing of its transcriptional regulation is not well understood. Here, we used the cichlid feeding apparatus to examine the transcriptional dynamics of skeletal plasticity over time. Using three closely related species that vary in their ability to remodel bone and a panel of 11 genes, including well-studied skeletal differentiation markers and newly characterized environmentally sensitive genes, we examined plasticity at one, two, four and eight weeks following the onset of alternate foraging challenges. We found that the plastic species exhibited environment-specific bursts in gene expression beginning at one week, followed by a sharp decline in levels, while the species with more limited plasticity exhibited consistently low levels of gene expression. This trend held across nearly all genes, suggesting that it is a hallmark of the larger plasticity regulatory network. We conclude that plasticity of the cichlid feeding apparatus is not the result of slowly accumulating gene expression difference over time, but rather is stimulated by early bursts of environment-specific gene expression followed by a return to homeostatic levels.