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The Caspian kutum, Rutilus frisii, is an anadromous fish native to Iran and despite the development of its hatchery production, its larval development has been poorly described; hence describing its morphological growth pattern was the aim of this study. The Caspian kutum larval period in the early development was divided into three stages, namely eleuthero-embryo (0–5 dph), propterygio-larvae (5–13 dph), pterygio-larvae (13–20 dph) and after larval period early juvenile was initiated (> 20 dph). The eleuthero-embryo stage was characterized by the commencement of mix-feeding while the yolk-sac remains, while propterygio-larvae absorbed the yolk-sac and continued to develop feeding apparatus and fin-folds. In pterygio-larvae, the fins developed and squamation began to appear. During the eleuthero-embryo stage, allometry in the head, trunk and tail were nearly isometric, negative, and positive, respectively. In propterygio-larvae, the head and tail allometry were positive, while the trunk was still negative. By the pterygio-larval stage, the tail and trunk allometry were nearly isometric but the head was positive. After metamorphosis, the growth pattern changed as the head and trunk allometry became nearly isometric and positive, respectively, but the tail allometry remained almost isometric. The results confirmed that morphological development and growth patterns during early life stages in R. frisii closely match its immediate required function. [ABSTRACT FROM AUTHOR]

The linkage between growth rate and feeding success has been shown to strengthen the effects of early growth rate on later growth rate in the early life history of fish. However, the growth–feeding linkage largely remains to be tested at the individual level within the same populations/cohorts. We examined the growth–feeding linkage for multiple populations/cohorts in Japanese anchovy Engraulis japonicus larvae and Pacific round herring Etrumeus micropus larvae, through otolith microstructure analysis, based on samples collected from the commercial fishery for larval fish in the Kii Channel, Japan. The three growth–feeding mechanisms, which are based on the respective potential advantages of larger somatic size, higher growth rate, and earlier morphological development for achieving feeding success, were tested to understand how growth rate relates to feeding success. The "somatic size" mechanism was supported for all of six samples for anchovy larvae and three of four samples for round herring larvae. The "growth rate" mechanism was supported for two of six samples for anchovy larvae and three of four samples for round herring larvae. The "morphological development" mechanism was supported for three of four samples for anchovy larvae and all of three samples for round herring larvae. Overall, the present analysis supported the growth–feeding linkage but revealed the dynamics of the growth–feeding mechanisms. All the mechanisms were shown to operate at least for certain populations/cohorts, but none of them were universally effective over all populations/cohorts across the two species. Understanding the dynamics of the growth–feeding mechanisms would provide precious hints for considering strategies of predicting recruitment dynamics. [ABSTRACT FROM AUTHOR]

Simple Summary: The cultivation of the Pacific fat sleeper (Dormitator latifrons) is of commercial interest in the Eastern Central Pacific. Its domestication potential is affected by the presence of pathogens. This study aimed to identify two trichodinid ectoparasites that are associated with D. latifrons larval mortality. We evaluated a total of 4320 fish larvae, 1080 fish larvae per treatment, revealing the presence of T. acuta and T. compacta in one treatment. Larval mortality in the infected treatment reached up to 58% by the fourth day post-hatching, at 28 °C, due to Trichodina infestation, resulting in significantly lower survival in the infected tanks compared to the uninfected tanks. This is the first geographical record of these protozoan parasites in a species that is native to the East Central Pacific Basin and intended for culture. Trichodinidae, a prevalent group of protozoan ectoparasites in aquaculture, cause rapid mortality in fish hatcheries. Despite their significance, knowledge about these parasites in farmed fish in South America, especially in native species that are currently being domesticated for aquaculture, remains limited. This study morphologically characterized the Trichodinid species that are infecting Pacific fat sleeper (Dormitator latifrons) larvae and evaluated their impact on larval rearing. Four pairs of broodstock were induced with GnRHA implants and placed in tanks containing 200 L of freshwater, with a water temperature of 28 ± 1.0 °C and a dissolved oxygen level of 4.00 ± 1.23 mg L−1, with partial water exchanges being performed daily. The larvae hatched 7 to 8 h after fertilization and were transferred to tanks containing water with the same quality parameters. Twelve hours post-hatching, the presence of Trichodina was observed. Every 24 h, 60 larvae per tank (n = 180 per treatment) were sedated, and larval wet mounts were prepared, air-dried at room temperature, and impregnated with silver nitrate. Infection parameters and daily mortality were calculated. Trichodina was observed to parasitize the pelvic fins, caudal fins, and heads of fish larvae, which showed lethargy and erratic swimming movements. The Trichodina species showed a daily increase in the infection parameters, and a 58% rate of larval mortality was observed at the fourth day post-hatching (dph) in the infected tanks. In captivity, D. latifrons larvae typically survive up to 7 days post-hatching (dph) before reaching their point of no return due to the lack of adequate diet and feeding regimes. However, our study indicates that Trichodina infestation accelerates mortality, causing infected larvae to die more quickly than uninfected ones. [ABSTRACT FROM AUTHOR]

Introduction: The availability of high-quality gilthead seabream (Sparus aurata) larvae in larviculture represents a major bottleneck to the aquaculture. This challenge can be compounded by losses resulting from the emergence of a clinical disorder's symptomatology. In this study, the observed syndrome included a rotated positioning of the larval sagittal plane and in most cases leading eventually to death. Methods: Herein, we examined using amplicon sequencing of the 16S rDNA the bacterial communities associated with S. aurata larvae at different conditions (including both fish with no evidence of the syndrome and fish with syndrome) during the early developmental stages along with the contribution of rearing water, organic matter and provided feed in the microbiota during an experiment of 18 days. Results: Over the development of larvae, differences were observed in the bacterial composition between healthy and symptomatic larvae as well as between components of the system. A remarkable presence of members of the Psychrobacter genus was observed in symptomatic larvaewith a significant increase at 18dph. The healthy larvae harbor different bacterial profile with a dominance of Vibrio and Bacillus genera during 3-8dph, various members of Alphaproteobacteria during 11-14dph and Marinifilum at 18dph. The rearing water showed a different bacterial profile compared to the other components, with a slight effect of healthy larvae at 3-8dph. The bacteriome of feeds provided during the rearing of larvae was found to be diverse. Chlorella was mainly dominated by members of Firmicutes, while Rotifer and Artemia were mainly dominated bymembers of Proteobacteria including different species of Psychrobacter. At 18dph, Artemia feed seems to affect the symptomatic larvae bacteriome, where it enhanced the presence of Psychrobacter spp. Discussion: Interestingly, the comparative network analysis at 18dph indicated that the bacterial associations in symptomatic larvae were primarily driven by members of the Psychrobacter genus. While various phyla contributed to bacterial associations in healthy larvae with different frequencies including mainly members of Proteobacteria, Bacteroidota and Firmicutes phyla. Finally, the Gammaproteobacteria/Alphaproteobacteria ratio was found to be related to the health condition of larvae. This study provides valuable informationwhich can be used as indicators for monitoring the health status of S. aurata larvae. [ABSTRACT FROM AUTHOR]

Largemouth bass is one of the most important freshwater aquaculture species in China. However, the mechanisms underlying the development of skeleton in the teleosts are not fully comprehensive. In a previous study in our laboratory, it was found that the addition of phospholipids to the diet significantly reduced the malformation rate of largemouth bass larvae. The malformation rate decreased from 91.29 ± 1.05% in the fish fed phospholipid-deficient diet (SP_L) to 11.99 ± 1.19% in the fish fed with diet including 8% phospholipids (SP_H). Therefore, high-throughput RNA-Seq was used to compare the transcriptome of largemouth bass larvae between SP_H and SP_L. Thirty whole body samples originated from 3 tanks in 8% phospholipids inclusion group and 3 tanks in no phospholipids inclusion group were used to reduce inaccuracies. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analyses revealed that the differentially expressed genes were involved in the mitogen-activated protein kinase (MAPK) signaling pathway, phosphatidylinositol signaling system, glycosphingolipid biosynthesis-lacto and neolacto series, and fatty acid degradation. Among the 584 differentially expressed genes, we paid attention to 6 genes known to be involved in skeletal development. Twist-related protein 2 (twist2) and dishevelled-associated activator of morphogenesis 1 (daam1), two genes related to osteoblast development, were up-regulated in SP_H. Bone gamma-carboxyglutamate (gla) protein (bglap), gene associated with the skeletal development and osteohormatology, was also up-regulated in SP_H. Procollagen C-endopeptidase enhancer b (pcolce b), a gene related to the development of gristle, was up-regulated in SP_H. Higher expression of secretory calcium-binding phosphoprotein 1 and 7 (scpp1 and scpp7) in SP_H suggests the stimulation of process related with tooth and bone development. The trend changes of the above genes all indicated that the lack of phospholipids might affect the skeletal development through the regulation of the expression of genes involved in several biological processes related to bone formation. In summary, those results provided valuable information about the reduction of deformity rates in largemouth bass and contributed to our understanding of the molecular mechanisms and regulative pathways regulating skeletal growth in larval carnivorous fish. [ABSTRACT FROM AUTHOR]

Elucidating physical transport phenologies in large lakes can aid understanding of larval recruitment dynamics. Here, we integrate a series of climate, hydrodynamic, biogeochemical, and Lagrangian particle dispersion models to: (1) simulate hatch and transport of fish larvae throughout an illustrative large lake, (2) evaluate patterns of historic and potential future climate‐induced larval transport, and (3) consider consequences for overlap with suitable temperatures and prey. Simulations demonstrate that relative offshore transport increases seasonally, with shifts toward offshore transport occurring earlier during relatively warm historic and future simulations. Intra‐ and inter‐annual trends in transport were robust to assumed pelagic larval duration and precise location and timing of hatching. Larvae retained nearshore generally encountered more favorable temperatures and zooplankton densities compared to larvae transported offshore. Larval exploitation of nearshore resources under climate change may depend on a concomitant shift to earlier spawning and hatch times in advance of earlier offshore transport. [ABSTRACT FROM AUTHOR]

In order to investigate the reproductive dynamics of the ichthyofauna in the Brazilian Pantanal, this study examines the spatial and temporal distribution of ichthyoplankton, taxonomic composition, and its correlation with environmental factors within one of the most important sub‐basins, the Taquari River. Egg and larvae collections were conducted at 11 sampling points between October and March of 2017/2018 and 2018/2019. Significant differences were observed between collection points, months, and years, with higher ichthyoplankton densities in the Coxim and Taquari rivers, particularly between November and January. Twenty‐eight genera and/or species of fish were identified, including 10 long‐distance migratory species. Egg density showed a negative correlation with water temperature and rainfall. For larvae, water transparency and rainfall were both significant, negatively influencing larval abundance. However, different species tend to occur in environments with distinct abiotic qualities. Yolk‐sac, preflexion, and flexion larval development stages were distributed throughout the sub‐basin, especially near the Pantanal. Considering the data and analyses presented in this study, the importance of connectivity between these environments, specifically between the plateau and Pantanal, is evident, highlighting the significance of the entire sub‐basin for fish reproductive processes. Therefore, research focusing on the ecological processes influencing the distribution of ichthyoplankton offers valuable insights for ecosystem conservation and aids in effective environmental management. [ABSTRACT FROM AUTHOR]

Many animals undergo indirect development, where their embryogenesis produces an intermediate life stage, or larva, that is often free‐living and later metamorphoses into an adult. As their adult counterparts, larvae can have unique and diverse morphologies and occupy various ecological niches. Given their broad phylogenetic distribution, larvae have been central to hypotheses about animal evolution. However, the evolution of these intermediate forms and the developmental mechanisms diversifying animal life cycles are still debated. This review focuses on Spiralia, a large and diverse clade of bilaterally symmetrical animals with a fascinating array of larval forms, most notably the archetypical trochophore larva. We explore how classic research and modern advances have improved our understanding of spiralian larvae, their development, and evolution. Specifically, we examine three morphological features of spiralian larvae: the anterior neural system, the ciliary bands, and the posterior hyposphere. The combination of molecular and developmental evidence with modern high‐throughput techniques, such as comparative genomics, single‐cell transcriptomics, and epigenomics, is a promising strategy that will lead to new testable hypotheses about the mechanisms behind the evolution of larvae and life cycles in Spiralia and animals in general. We predict that the increasing number of available genomes for Spiralia and the optimization of genome‐wide and single‐cell approaches will unlock the study of many emerging spiralian taxa, transforming our views of the evolution of this animal group and their larvae. [ABSTRACT FROM AUTHOR]

Objective: The copepod Parvocalanus crassirostris has recently increased its use as live food in marine fish hatcheries. Methods: To investigate the bacterial community of P. crassirostris nauplii and explore the potential use of nauplii as a vector for probiotics, adult copepods were reared with or without a probiotic consortium (Bacillus spp. and Lactobacillus spp.). Nauplii from both treatments were either enriched with probiotics or not, resulting in four treatments: control rearing and nonenriched, control rearing and probiotic enriched, probiotic rearing and nonenriched, and probiotic rearing probiotic enriched. A next‐generation sequencing analysis of the 16S ribosomal RNA gene was performed. Result: The bacterial community of nauplii without probiotics was dominated by the phyla Proteobacteria (mean ± standard deviation = 51.5 ± 8.0%) and Bacteroidetes (27.6 ± 6.7%); from these phyla, the most abundant orders were Rhodobacterales (21.8 ± 2.0%), Flavobacteriales (13.5 ± 9.4%), Chitinophagales (9.7 ± 1.8%), Alteromonadales (9.5 ± 4.0%), and Burkholderiales (3.8 ± 0.8%). Opportunistic pathogenic bacterial genera, such as Vibrio spp. and Pseudomonas spp., were detected at very low relative abundances (<1.2%), indicating that P. crassirostris nauplii could be considered a safe microbiological live feed. Furthermore, P. crassirostris nauplii were a good vector for probiotics delivery, as the adhesion of probiotics on the copepod exoskeleton was successful. Bacillus spp. abundance was 5–6× greater than the abundance of Lactobacillus spp. in P. crassirostris nauplii. The highest mean values of probiotics relative abundance (Bacillus spp. 41 ± 6.0%, Lactobacillus spp. 6.0 ± 3.0%) were observed in nauplii that were reared with probiotics and also enriched with probiotics. Conclusion: Parvocalanus crassirostris nauplii stages I–II appear to be good vectors to provide probiotics to first‐feeding fish larvae. Impact statementMarine fish aquaculture relies on quality live feed for optimal protein production. Assessing copepod nauplii's microbiological safety as fish larvae prey and their role as probiotics vectors is an important contribution to marine fish aquaculture. [ABSTRACT FROM AUTHOR]

The eastern North Pacific is simultaneously experiencing ocean warming (OW) and ocean acidification (OA), which may negatively affect fish early life stages. Pacific cod (Gadus macrocephalus) is an economically and ecologically important species with demonstrated sensitivity to OW and OA, but their combined impacts are unknown. Through a ~ 9-week experiment, Pacific cod embryos and larvae were reared at one of six combinations of three temperatures (3, 6, 10 °C) and two CO2 levels (ambient: ~ 360 μatm; high: ~ 1560 μatm) in a factorial design. Both embryonic and larval mortality were highest at the warmest temperature. Embryonic daily mortality rates were lower under elevated CO2 and there was no effect of CO2 level on larval daily mortality rates. Growth rates of young larvae (0 to 11 days post-hatch) were faster at warmer temperatures and at high CO2 levels, but growth during the 11–28 days post-hatch interval increased by temperature alone. The condition of larvae decreased with age, but less markedly under high CO2 levels. However, at 6 °C, fish incubated in ambient CO2 remained in higher condition than fish in the high CO2 treatment throughout the experiment. Overall, temperature had the greater influence on Pacific cod early life stages across each measurement endpoint, while CO2 effects were more modest and inconsistent. Subtle developmental differences in larval Pacific cod could be magnified later in life and important in the context of recruitment. These results show the complexity of stage- and trait-specific responses to and value of investigating the combined effects of co-occurring climatic stressors. [ABSTRACT FROM AUTHOR]

Peres fish (Osteochilus kappenii) is a native freshwater fish in Central Aceh, Indonesia. This study aimed to determine the morphology and histology development of the digestive tract of Peres larvae. Understanding the developmental stages is essential to support the success of larval rearing during ontogeny. The parameters observed include the total length (TL) of larvae, daily growth rate, larval morphology, and histology of the digestive tract. Furthermore, the total length of the larvae was measured from 1 to 25 day after hatching (DAH). The larvae sampling was conducted at 1, 2, 3, 4, 8, 10, 15, 20, and 25 DAH. Morphological and histological observations were carried out microscopically, and data were analyzed descriptively. The results showed that the TL of larvae growth at the beginning (1 DAH) and termination (25 DAH) of the study was 4.58 ± 0.24 mm and 9.62 ± 0.79 mm, respectively. Based on the structural development of the body and food sources, the development of percussion larvae was divided into four phases, namely the yolk sac (0-4 DAH), pre-flexion (5-15 DAH), flexion (16-20 DAH), and post-flexion (21-25 DAH). The yolk was completely absorbed 4 DAH, marking the end of the yolk sac phase, as the Peres fish larvae began to use external feed. At 25 DAH, the larval morphology was fully formed and pigmentation spread throughout the body. The digestive organs and glands are well-developed with differentiation of the midgut and hindgut, increased goblet cells in the intestine, and increased lipid vacuoles in the liver and zymogen in the pancreas to utilize feed optimally. [ABSTRACT FROM AUTHOR]

Simple Summary: The increasing world population generates a huge volume of food waste. The use of black soldier fly larvae in the bioconversion of food waste is a new approach and an interesting example of a sustainable, circular economy approach. In this study, different food waste and residues (ranging from a vegetable to a carnivorous diet) were used as rearing substrates for black soldier fly larvae. The effects of different substrates on larvae development, bioconversion efficiency, and variations in surface temperatures were investigated. The results highlighted how an omnivorous diet provides performances comparable to the high-quality substrate diet (commercial chicken feed) and, therefore, can represent an effective strategy for rearing larvae while reducing food waste. Black soldier fly larvae (BSFL) can utilize food by-products or residues for growth, benefiting farm animal's diets' production sustainability. The experiment aimed to assess the effect of different substrate compositions on larval growth, chemical composition, and substrate temperature. BSFL were allocated to one of the four diets (control, vegetable, carnivorous, and omnivorous) for the entire experiment (8 days). The temperature was measured twice daily using a thermal-imaging camera, and the accumulated degree hours (ADH) was calculated. The results showed that the larvae fed the vegetable diet exhibited a significantly reduced growth performance, with a biomass reduction of 26.3% compared to the control diet; furthermore, vegetable-fed larvae showed a lower dry matter content (−30% compared to the average of other diets) due to lower fat content (−65% compared to average of other diets). The nutritional composition of larvae fed an omnivorous diet was similar to larvae fed a high-quality substrate diet (control diet-chicken feed), indicating that the omnivorous diet could be an ideal solution for rearing BSFL larvae; however, the current European legislation prohibits the use of animal meal. The study also revealed that substrate temperatures did not have a discernible influence on larval growth, further emphasizing the importance of diet in BSFL rearing strategies. [ABSTRACT FROM AUTHOR]

Due to their distinctive look, seahorses are famous in the aquarium trade and traded worldwide for their alleged therapeutic benefits. The present study was conducted to identify the causative agents for larval mortality of Hippocampus kuda and to find a treatment to reduce larval mortality at an ornamental fish hatchery in Sri Lanka. Bacteria causing vibriosis in H. kuda larvae were isolated and identified using morphological and biochemical tests. The disc diffusion method was used with 30 µg of chloramphenicol, streptomycin, tetracycline and ampicillin to evaluate antibiotic susceptibility of isolated bacteria. As pathogenic vibrios were more sensitive to tetracycline, the experimentally infected H. kuda larvae were exposed to 20-50 µg/L tetracycline for 30 days. V. alginolyticus, Vibrio splendidus, V. parahaemolyticus, V. mimicus, Aeromonas hydrophila and Plesiomonas shigelloides were found in H. kuda larvae, while V. alginolyticus and V. splendidus were encountered repeatedly. V. alginolyticus, V. mimicus, V. fluvialis, Aeromonas sp., Micrococcus spp., M. leteus and Bacillus circulans were identified from the larval culture water. V. alginolyticus was sensitive to chloramphenicol and tetracycline, while V. splendidus was sensitive to tetracycline. Tetracycline, 30 mg/L as a bath treatment, effectively treats vibriosis in larval rearing tanks of H. kuda. [ABSTRACT FROM AUTHOR]

Hatching corresponds to the moment an individual leaves its egg envelope. Yet, hatching has scarcely aroused the interest of biologists, and the question posed here, 'why do larvae hatch when they do?' appears to have been rarely asked. In this proof-of-concept study, we tested the hypothesis that fish larvae hatch when a specific ratio between egg surface area (ESA) and larval surface area (LSA) is reached, irrespective of egg diameter and abiotic factors. An estimated mean ratio of 1: 1.52 (CI = 1.39–1.63) was obtained from the eggs of 33 species of teleosts, with diameters ranging from 0.63 to 5.7 mm. We assume that this ratio has a value beyond which the oxygen supply through the egg surface cannot cope with the oxygen requirements of the embryo. The detailed ecological consequences are unknown but can be expected to impact fisheries and aquaculture negatively. [ABSTRACT FROM AUTHOR]

Tonic immobility is an antipredator defence in which the prey animal remains motionless after physical contact with the predator, pretending to be dead. This behaviour has been observed among a variety of taxa but has received only little attention in amphibian larvae. During our field studies with fire salamander larvae, we observed that larvae from different habitats display tonic immobility after handling. In our study site, we find larvae in pond and stream habitats, that differ in several aspects such as their stress response and their risk‐taking behaviour, likely caused by the very different habitat conditions. We measured the time that the tonic immobility behaviour was displayed but found no difference between larvae from the two habitat types. Likewise, we also found no correlation between the size of the larvae and the duration of displaying the behaviour. In conclusion, we found that fire salamander larvae show tonic immobility, but found no evidence that the different habitat conditions influence the tonic immobility behaviour. [ABSTRACT FROM AUTHOR]

Most likely, the alien snow crab Chionoecetes opilio entered the Kara Sea from the Barents Sea, both due to the migration of adults and with currents at the larval stage. Currently, all bottom stages, including mature individuals and a large number of pelagic larvae, are present in the Kara Sea. However, the origin of larvae has not yet been clarified. The larvae hatched in the Kara Sea should be at an earlier stage of development compared with the larvae arrived here from the Barents Sea due to later development of phytoplankton and, accordingly, later hatching. The larvae of the snow crab Chionoecetes opilio and the spider crab Hyas araneus were collected in the central and southwestern Kara Sea in July–early August 2019 by a Bongo zooplankton net with a diameter of 60 cm. It was established that the larvae were unevenly distributed across the Kara Sea. The most populus region was the border with the Barents Sea in the St. Anna Trough (up to 860 ind./m2), and relatively high concentrations of larvae were recorded in the southwestern part, where their abundance at stations varied from 18 to 302 ind./m2. In the zone of the Ob–Yenisei plume, crab larvae were absent or their abundance was minimal. Using molecular genetic methods, the species identity of 361 larvae (344 C. opilio and 17 H. araneus) was reliably determined, and measurements of a number of morphological structures were made for 401 larvae. Significant differences in size were found at the zoea II stage between C. opilio and H. araneus. In July 2019, in most of the Kara Sea, in zooplankton samples, crab larvae were represented by zoea I of C. opilio with rare specimens of zoea I of H. araneus of the Kara Sea origin. Only in the southwestern part, at the boundary with the Barents Sea, was the presence of zoea II of C. opilio and H. araneus observed in samples with an increased share of the latter species in catches, which probably originated from the Barents Sea. [ABSTRACT FROM AUTHOR]

Per‐ and polyfluoroalkyl substances (PFAS) are widely used in many industrial and domestic applications, which has resulted in unintentional human exposures and bioaccumulation in blood and other organs. Perfluorooctane sulfonate (PFOS) is among the most prevalent PFAS in the environment and has been postulated to affect brain functions in exposed organisms. However, the impacts of PFOS in early neural development have not been well described. We used zebrafish larvae to assess the effects of PFOS on two fundamental complex behaviors, prey capture and learning. Zebrafish exposed to PFOS concentrations ranging from 2 to 20 µM for differing 48‐h periods were viable through early larval stages. In addition, PFOS uptake was unaffected by the presence of a chorion. We employed two different experimental paradigms; first we assessed the impacts of increasing organismal PFOS bioaccumulation on prey capture and learning, and second, we probed stage‐specific sensitivity to PFOS by exposing zebrafish at different developmental stages (0–2 vs. 3–5 days post fertilization). Following both assays we measured the amount of PFOS present in each larva and found that PFOS levels varied in larvae from different groups within each experimental paradigm. Significant negative correlations were observed between larval PFOS accumulation and percentage of captured prey, whereas nonsignificant negative correlations were observed between PFOS accumulation and experienced‐induced prey capture learning. These findings suggest that PFOS accumulation negatively affects larval zebrafish's ability to perform complicated multisensory behaviors and highlights the potential risks of PFOS exposure to animals in the wild, with implications for human health. Environ Toxicol Chem 2024;43:847–855. © 2023 SETAC [ABSTRACT FROM AUTHOR]

Background: Apoptosis is involved (directly and indirectly) in several physiological processes including tissue remodeling during the development, the turnover of immune cells, and a defense against harmful stimuli. The disordered apoptotic process participates in the pathogenesis of various diseases, such as neoplasms, and chronic inflammatory or systemic autoimmune diseases, which are associated with its inadequate regulation. Caspases are vital components of the apoptotic pathway that are involved in developmental and immune processes. However, genome-wide identification and functional analysis of caspase have not been conducted in Mytilus coruscus, which is an economically important bivalve. Results: Here, 47 caspase genes were identified from the genomes of M. coruscus, and the expansion of caspase-2/9 and caspase-3/6/7 genes were observed. Tandem duplication acts as an essential driver of gene expansion. The expanded caspase genes were highly diverse in terms of sequence, domain structure, and spatiotemporal expression profiles, suggesting their functional differentiation. The high expression of the expanded caspase genes at the pediveliger larvae stage and the result of apoptosis location in the velum suggest that the apoptosis mediated by them plays a critical role in the metamorphosis of M. coruscus larvae. In gill, caspase genes respond differently to the challenge of different strains, and most caspase-2/9 and caspase-3/6/7 genes were induced by copper stress, whereas caspase-8/10 genes were suppressed. Additionally, most caspase genes were upregulated in the mantle under ocean acidification which could weaken the biomineralization capacity of the mantle tissue. Conclusions: These results provide a comprehensive overview of the evolution and function of the caspase family and enhanced the understanding of the biological function of caspases in M. coruscus larval development and response to biotic and abiotic challenges. [ABSTRACT FROM AUTHOR]

We evaluated the potential of the euryhaline copepod Pseudodiaptomus inopinus as a prey to enhance the feeding activity of red sea bream Pagrus major larvae. Pseudodiaptomus inopinus was used to evaluate free amino acid composition and dietary effects on the rearing performance of fish larvae, in comparison to rotifers (control prey). Among free amino acids, alanine, arginine, and glycine were markedly higher in P. inopinus than in rotifers. Larvae were reared for 20 days post-hatching under three feeding treatments: rotifers (control), rotifers supplemented with copepods, and copepods only. Larvae fed copepods alone had a higher growth rate than those in the other treatments. However, the survival rates of these larvae were lower than those under control or copepod supplementation. While equivalent stocking densities of rotifers were employed in the rearing water for both larvae, whether supplemented with copepods or not, the supplemented treatment yielded diminished larval survival and failed to enhance growth rates. According to gut content analysis, larvae receiving supplemented treatment preferentially fed on copepods, and the number of ingested rotifers was reduced. As a result, total ingested mass was lower in the supplemented larvae. This study suggests that copepods containing free amino acid species negatively affect prey acceptance of fish larvae. [ABSTRACT FROM AUTHOR]

Identifying factors that affect larval mortality is critical for understanding the drivers of fish population dynamics. Although larval fish mortality is high, small changes in mortality rates can lead to large changes in recruitment. Recent studies suggest maternal provisioning can dramatically affect the susceptibility of larvae to starvation and predation, the major sources of early‐life mortality. We measured otolith core width‐at‐extrusion and validated that this is a proxy for larval size‐at‐extrusion for eight species of rockfishes (genus Sebastes) to examine the influence of initial larval size on larval growth and survival and to understand how oceanographic conditions experienced by gestating females affect larval size (i.e., quality). Otolith core width‐at‐extrusion was significantly positively related to larval rockfish recent growth rate (5/7 species with sufficient sample size) and survival (all eight species). This suggests that individuals that are larger at extrusion generally grow faster and are more likely to survive early life stages. Otolith core width‐at‐extrusion was positively related to higher presence of Pacific Subarctic Upper Water and was negatively related to warmer, saline waters at the depths gestating mothers inhabited during the months prior to larval collection. In addition, otolith core width was larger further from fishing ports, possibly because these locations were historically less fished, contained more older, larger females, and/or had inherently better habitat quality (higher Pacific Subarctic Upper Water) than sites closer to shore. These results indicate that the environmental conditions female rockfish experience during gestation drive the size of the larvae they produce and impact larval growth and survival. [ABSTRACT FROM AUTHOR]

This study evaluated the effect of the co-feeding (C) period on the growth and survival of larvae of the yo-yo loach Botia lohachata ornamental species during the weaning period from live food (LF) to inert food (IF). The breeders were subjected to induced spawning using crude pituitary homogenate. A total of 2,400 larvae were used with an average initial weight of 0.39 ± 0.09 mg and an average total length of 4.08 ± 0.21 mm, from a single breeding pair. The live food was newly hatched nauplii of Artemia franciscana, and the inert diet was a commercial ration with 55% crude protein and two particle sizes (142-350 µm and 350-500 µm). As the first food, all larvae received A. franciscana during the first six days, except for the fasting (NC) and inert food (IF) groups. The following co-feeding strategies were employed: C4 = 4 days of co-feeding, C8 = 8 days of co-feeding, C12 = 12 days of co-feeding, and LF = Artemia during the entire experimental period. The longest period with live food promoted better larval growth rates. The specific growth rate of larvae fed live food during the entire period (LF) was higher than that of the other groups, followed by the co-feeding strategies. There was no effect (P > 0.01) on larval survival in the LF, C12, C8, and C4 groups, which ranged from 41% to 53% after 30 days. Treatment R resulted in high mortality and low growth, suggesting that live food should be the first food source for B. lohachata larvae. [ABSTRACT FROM AUTHOR]

The intracohort cannibalism present in tropical gar larvae (A. tropicus) generates great problems in its culture, as in other fish species around the world. The addition of tryptophan (Trp) (10, 20, and 30 g/kg) and a control diet (CD) without Trp were evaluated in A. tropicus larvae regarding growth, survival, cannibalism, behavior, digestive enzymatic activity, and genes related to aggressiveness and/or cannibalism in two stages: 0–13 days after hatching (DAH); and only cannibals (14–24 DAH). In the first stage, no differences were observed in growth parameters; cannibalism was lower with the use of Trp, with the lowest percentage being the 10 g/kg Trp treatment (56.75 ± 2.47%) compared to CD (64.75 ± 1.76%). In the second stage, survival was greater in 10 g/kg Trp (75.00 ± 7.07%) than in CD (23.33 ± 5.77%). Thus, cannibalism was lower with 10 g/kg Trp (20.0 ± 10.0%) compared to CD (76.66 ± 5.77%). Cannibal larvae fed with 10 g/kg Trp had a greater enzymatic activity in acid and alkaline proteases and leucine aminopeptidase, as well as the overexpression of avpi1, crh, and htr1a and the subexpression of tph1, th, sstr1, and hdc (p < 0.05). No aggressive behaviors were recorded in the larvae fed with the 10 g/kg Trp treatment, unlike those fed with CD. The use of 10 g/kg Trp improves survival and reduces cannibalism in A. tropicus larvae. [ABSTRACT FROM AUTHOR]

Dietary supplementation with Omega-3 fatty acids seems to promote skeletal health. Therefore, their consumption at imbalanced or excessive levels has offered less beneficial or even prejudicial effects. Fish produced in aquaculture regimes are prone to develop abnormal skeletons. Although larval cultures are usually fed with diets supplemented with Omega-3 Long Chain Polyunsaturated fatty acids (LC-PUFAs), the lack of knowledge about the optimal requirements for fatty acids or about their impact on mechanisms that regulate skeletal development has impeded the design of diets that could improve bone formation during larval stages when the majority of skeletal anomalies appear. In this study, Argyrosomus regius larvae were fed different levels of Omega-3s (2.6% and 3.6% DW on diet) compared to a commercial diet. At 28 days after hatching (DAH), their transcriptomes were analyzed to study the modulation exerted in gene expression dynamics during larval development and identify impacted genes that can contribute to skeletal formation. Mainly, both levels of supplementation modulated bone-cell proliferation, the synthesis of bone components such as the extracellular matrix, and molecules involved in the interaction and signaling between bone components or in important cellular processes. The 2.6% level impacted several genes related to cartilage development, denoting a special impact on endochondral ossification, delaying this process. However, the 3.6% level seemed to accelerate this process by enhancing skeletal development. These results offered important insights into the impact of dietary Omega-3 LC-PUFAs on genes involved in the main molecular mechanism and cellular processes involved in skeletal development. [ABSTRACT FROM AUTHOR]

The present study was conducted to evaluate the growth and survival rates of common carp (Cyprinus carpio) larvae fed different diets levels in laboratory Two-day-old larvae were transferred from the University of Basrah Marine Science Center hatchery to the Abi Al-Khaseeb district's experiment laboratory. The larvae were distributed into four treatments 450 larvae each treatment (150 larvae per replicate and three replicates per treatment) at a stock density of 3.33 larvae/L. The treatments were as follows: T1 was given boiling egg yolks; T2 was given a processed diet with 45% protein; T3 was given Redi-Lac milk powder; and T4 was given ground Artemia eggs. The experiment ran for 20 days, beginning on April 17, 2022. The results showed that larvae fed on diet containing ground Artemia eggs (T4) produced the highest final weight (39.667mg), followed by a diet containing 45% protein processed diet (T2), Redi-Lac milk powder food (T3), and boiled egg yolks food (T1) produced the lowest final weight (27.333 and 24.667 mg, respectively) Statistical analysis revealed a significant difference (P≤0.05) in the final weight, weight gain, daily growth rate, relative growth rate and specific growth rate between T4 and T1, but not between T4 and T2 and between T4 and T3. The survival rate showed a significant difference (P≤0.05) between T4 (0.71%) and other treatments. Our results suggest that ground Artemia eggs is the most suitable and optimal meal for common carp fish larvae. [ABSTRACT FROM AUTHOR]

This study presents a comprehensive morphological examination of the larval development stages and growth rates of Cyprinion macrostomus. C. macrostomus broodstock have been collected from their natural habitats in Kangal, Sivas, Türkiye, and taken into cultivation under laboratory conditions. The research meticulously observed the early developmental stages, feeding behaviors, and growth rates of the larvae. Findings indicate significant morphological changes during the transformation of larvae into juvenile fish, with morphological metamorphosis completed by day 25. The average length of the larvae reached 14.78 mm by the end of day 25. This study provides fundamental information for the cultivation and conservation of C. macrostomus, identifying necessary conditions for optimizing larval growth and development processes. Moreover, this research contributes to the development of strategies for the sustainable management and conservation of C. macrostomus, offering a foundation for future studies to build upon for the species’ conservation and successful aquaculture cultivation. [ABSTRACT FROM AUTHOR]

The coexistence of polystyrene (PS) and polypropylene (PVC) microplastics (MPs) and methamphetamine (METH) in aquatic systems is evident. However, the joint toxicity is unclear. Here, zebrafish larvae were exposed to single PS and PVC MPs (20 mg L−1) and combined with METH (250 and 500 μg L−1) for 10 days. The results indicated that acute exposure to PS and PVC MPs induced lethal effects on zebrafish larvae (10–20%). Treatment with MPs markedly suppressed the locomotion of zebrafish, showing as the lengthy immobility (51–74%) and lower velocity (0.09–0.55 cm s−1) compared with the control (1.07 cm s−1). Meanwhile, histopathological analysis revealed pronounced depositions of MPs particles in fish's intestinal tract, triggering inflammatory responses (histological scores: 1.6–2.0). In the coexposure groups, obviously inflammatory responses were found. Furthermore, the up-regulations of the genes involved in the oxidative kinase gene and inflammation related genes implied that oxidative stress triggered by MPs on zebrafish larvae might be responsible for the mortality and locomotion retardant. The antagonistic and stimulatory effects of METH on the expression changes of genes found in PVC and PS groups implied the contrary combined toxicity of PS/PVC MPs and METH. This study for the first time estimated the different toxicity of PS and PVC MPs on fish and the joint effects with METH at high environmental levels. The results suggested PS showed stronger toxicity than PVC for fish larvae. The addition of METH stimulated the effects of PS but antagonized the effects of PVC, promoting control strategy development on MPs and METH in aquatic environments. [ABSTRACT FROM AUTHOR]

Larval attachment organs (LAOs) are unicellular or multicellular organs that enable the larvae of many actinopterygian fishes to adhere to a substrate before yolk‐sac absorption and the free‐swimming stage. Bowfins (Amiiformes) exhibit a sizable LAO on the snout, which was first described in the late 19th and early 20th centuries. In this study, we document the LAO of Amia ocellicauda (Richardson, 1836) using a combination of scanning electron microscopy (SEM) and light microscopy, and histochemistry. We examined material representing three stages with SEM ranging in size from 5.8 to 11.2 mm in notochord length and one stage histochemically. We compare the LAO of A. ocellicauda to that of the lepisosteid Atractosteus tropicus Gill, 1863 and show that although the LAOs of A. ocellicauda and A. tropicus are both super‐organs, the two differ in the ultrastructure of the entire organ. A. ocellicauda possesses two distinct lobes, with the organs arranged on the periphery with none in the middle, whereas A. tropicus also possesses two lobes, but with the organs scattered evenly across the super‐organ. The individual organs of A. ocellicauda possess adhesive cells set deep to support cells with the adhesive substance released through a pore, whereas A. tropicus possesses both support cells and adhesive cells sitting at a similar level, with the adhesive substance released directly onto the surface of the organ. We additionally provide a table summarizing vertebrate genera in which attachment organs have been documented and discuss the implications of our study for hypotheses of the homology of attachment organs in the Holostei. [ABSTRACT FROM AUTHOR]

It is an acknowledged theory that a faster growth rate, determined by various environmental drivers, may boost the survival of larval and juvenile fish. In this study we examined the differences in the growth rate of larval and juvenile cod (age 2 – 136 d; SL: 4.1 – 39.2 mm) between the years 2006 and 2014, sub-areas of the Baltic Sea (Bornholm Basin, BB; Słupsk Furrow, SF; Gdansk Basin, GB), and seasons (spring and summer). The average growth rate for all specimens was 0.25 mm/d, with significantly lower values between 2012 and 2014 than between 2006 and 2011. A reduction in zooplankton biomass, especially the large zooplankton fraction, was observed after the 2006–2008 period, which was related to the prevailing temperature conditions in the surface layers. The reduction in zooplankton biomass was accompanied by changes in the structure of zooplankton: less T. longicornis, C. hamatus, and Pseudocalanus spp., and more Acartia spp. The results suggest that the inter-annual differences observed in zooplankton biomass and structure are likely responsible for the observed reduction in the growth rate of cod larvae between 2012 and 2014 compared to the years between 2006 and 2011. The growth rate reduction could be one of the reasons for the decline in the recruitment of eastern Baltic cod between the years 2013 and 2015, after the high recruitment years of the period 2011-2012. [ABSTRACT FROM AUTHOR]

Larval behaviour for many of New Zealand's diadromous freshwater fish is inadequately described. Diadromy for many amphidromous species is not obligatory however, and where conditions are suitable, freshwater larval rearing may be facilitated. Where this occurs in lakes, opportunities to document the composition and conditions supporting larval rearing exist. Boat trawling was undertaken across nine lowland lakes in the Lower Waikato over four consecutive winters with a focus on larval galaxiids. Galaxiid larvae were captured in surface water habitats in all but one lake, with banded kōkopu (Galaxias fasciatus) and giant kōkopu (Galaxias argenteus) the most common species detected. One lake, Lake Waahi, consistently resulted in the most galaxiid captures for effort expended. Analyses of larvae from this and other lakes indicated that two sizes predominated in catches and that larger, older larvae were predominantly G. fasciatus while smaller, younger larvae were predominantly G. argenteus. Stomach contents indicated that two non-native zooplankton species predominated in the diet of larvae, the Holarctic daphnia, Daphnia galeata, and the Australian calanoid copepod Boeckella symmetrica. This study provides new information regarding the timing, movement and predicted recruitment of native fish species in this river basin that has important implications for lake and river management. [ABSTRACT FROM AUTHOR]

Objective: The expansion of marine aquaculture requires the shipment of early life stages from hatcheries to breeding centers. Thus, maintaining water quality parameters during transportation is crucial. This experiment investigated the effects of a commercial probiotic mixture (PM) (consisting of Bacillus licheniformis, Bacillus subtilis, Pediococcus acidilactici, and Lactobacillus acidophilus with a total count of 107 CFU/g) on water quality, bacterial population, and the survival of larvae of Yellowfin Seabream Acanthopagrus latus during a 24‐h simulated transportation experiment. Methods: To simulate transportation, purified seawater was used as a control and purified seawater supplemented with 3 g of PM was used as the PM48 treatment. For the PM48 treatment, 3 g of PM was added to 1 L of purified seawater and mixed with 200 L of purified seawater 48 h prior to the main experiment. Result: The use of probiotics resulted in an increase in larval survival up to 93.3% compared with 89.85% in the control group. Initial sampling showed a statistically significant difference in NO2− levels between the control and PM48 treatments. After transportation, the pH of the control treatment showed a significant decrease. The total number of bacteria and the total number of Vibrio spp. in water and fish larvae showed that within 48 h, the probiotics became the dominant population in the PM48 treatment. After 24 h, water samples and larvae from the control treatment showed a significant increase in bacterial load. Conclusion: The results showed that probiotics can play a significant role in maintaining biotic and abiotic water quality parameters, leading to a better survival rate of larvae during transportation. These findings represent an important step in improving long‐distance transport protocols. Impact statementThe expansion of marine aquaculture requires the shipment of early life stages from hatcheries to breeding centers. Thus, maintaining water quality parameters with probiotics during transportation is crucial. [ABSTRACT FROM AUTHOR]

Drift by larval white sturgeon (Acipenser transmontanus) results in an ontological habitat shift during early life that may be influenced by changes in the trade‐off between mortality risk and growth potential. Despite the importance of early life history to recruitment and conservation, for many species, including white sturgeon, we have a limited understanding of the mechanistic drivers of drift. We tested if two biotic factors, conspecific density and timing of food availability during the yolksac larvae stage, influenced the timing of drift behaviour. We evaluated larval drift timing for yolksac larvae reared in laboratory mesocosms at two densities (10 or 20 larvae) and three feeding initiation times (before exogenous feeding, at the initiation of exogenous feeding, or starvation). We found that drift occurred at 13 days post‐hatch (dph) overall, 2 days after the shift from the yolksac stage to the feeding stage (11 dph at 14°C). The timing of food availability in the fed treatments did not affect the timing of larval drift, nor did the density of conspecifics. Starvation delayed drift timing by 2 days, to15 dph. This delay of drift from a habitat with no food availability may disadvantage starving larvae and reduce growth potential. [ABSTRACT FROM AUTHOR]

Background. Aquatic organisms demonstrate a high vulnerability to mortality when exposed to Pb, even at low concentrations. The objective of this investigation is to ascertain the histopathological alterations and cortisol concentrations in diverse tissues of Gambusia affinis, with a specific focus on the eggs and larvae, following exposure to varying concentrations of PbCl2. Methods. Adult specimens of G. affinis measuring 5-6 cm in length were obtained from a commercial fish breeding facility. A total of 8 fish with a 1 : 1 ratio of 4 pairs of broodstock were placed in an 8-liter aquarium. Following the adaptation phase, the broodstock underwent a spawning process that lasted for a duration of 7 days. Throughout the spawning process, assessments were conducted on the progression of the abdominal growth of the broodstock. Eggs ready to hatch and Gambusia larvae were taken and exposed to 0.1 mg/L PbCl2, 1 mg/L PbCl2, and control (without PbCl2) for 24 hours, with three replications. At the end of the experiment, histopathological analysis was conducted using the hematoxylin Ehrlich-eosin staining method and scanning electron microscopic (SEM) observation. The levels of Pb in gills were determined by employing atomic absorption spectrophotometer. The cortisol concentration in organ samples of fish was determined through the utilization of a cortisol ELISA Kit. Results. The findings of this investigation demonstrated an important bioaccumulation occurrence of Pb within the gills of Gambusia fish that were specifically subjected to 0.1 and 1 mg/L PbCl2. The histological structures of eggs and larvae that were subjected to PbCl2 exhibited impairment in comparison to the control group. The present study observed a significant elevation in cortisol levels among fish specimens that were subjected to PbCl2 exposure. Conclusions. The findings of this investigation suggest that the occurrence of Pb is linked to a rise in cortisol concentrations in various organs of G. affinis larvae. Furthermore, the research indicates that the exposure to Pb has a notable impact on the histological alterations in the eggs and larvae of Gambusia fish, implying that they are undergoing stress as a result of the Pb exposure. [ABSTRACT FROM AUTHOR]

H.G. Moser was not particularly well known regarding the Elopomorpha, but he began his seminal 1981 fish larvae morphology review by describing the mysteries of European eels and their leptocephali, and he eventually described some California Current leptocephali. Descriptions of all types of leptocephali and then microscope photographs have revealed complex pigmentation patterns and diverse body shapes that parallel the features of the other teleost fish larvae that his review showed so clearly, some of which appear to mimic gelatinous zooplankton (GZ). Most recently, underwater photographs and video of leptocephali indicate that predator avoidance through transparency, shape-change-mediated mimicry, or morphological features have evolved in response to natural selection from predation in ways generally similar to other fish larvae. Several families of leptocephali perform remarkable curling into round or flattened shapes or use expandable chromatophores when threatened, which appears to mimic GZ for predation reduction. Like a number of other teleost fish larvae, some leptocephali have body extensions or telescopic eyes, and at least one has a long caudal filament with pigmented swellings that is similar to the remarkable GZ mimicry appendages of some fish larvae. The morphology and use of mimicry of leptocephali in comparison to other fish larvae is reviewed as a tribute to H.G. Moser's remarkable career. [ABSTRACT FROM AUTHOR]

Tektins are a highly conserved family of coiled-coil domain containing proteins known to play a role in structure, stability and function of cilia and flagella. Tektin proteins are thought to form filaments which run the length of the axoneme along the inner surface of the A tubule of each microtubule doublet. Phylogenetic analyses suggest that the tektin family arose via duplications from a single tektin gene in a unicellular organism giving rise to four and five tektin genes in bilaterians and in spiralians, respectively. Although tektins are found in most metazoans, little is known about their expression and function outside of a handful of model species. Here we present the first comprehensive study of tektin family gene expression in any animal system, in the spiralian annelid Platynereis dumerilii. This indirect developing species retains a full ancient spiralian complement of five tektin genes. We show that all five tektins are expressed almost exclusively in known ciliary structures following the expression of the motile cilia master regulator foxJ1. The three older bilaterian tektin-1, tektin-2, and tektin-4 genes, show a high degree of spatial and temporal co-regulation, while the spiralian specific tektin-3/5A and tektin-3/5B show a delay in onset of expression in every ciliary structure. In addition, tektin-3/5B transcripts show a restricted subcellular localization to the most apical region near the multiciliary arrays. The exact recapitulation of the sequence of expression and localization of the five tektins at different times during larval development indicates the cooption of a fixed regulatory and cellular program during the formation of each ciliary band and multiciliated cell type in this spiralian. [Display omitted] • First comprehensive expression analysis of tektin s in any organism. • Three evolutionary older tektin paralogs are coexpressed in each ciliary band. • The expression for two evolutionary younger tektins is delayed. • Transcripts of the youngest tektin paralog are apically localized. • A sequence of first foxJ1 , then bimodal expression and apical localization of tektins is recapitulated in every ciliary band. [ABSTRACT FROM AUTHOR]

Since 2006, an ophidiiform larva with an ovoid body, elongate anterior dorsal-fin ray, and long trailing fleshy filament has been identified as Pycnocraspedum squamipinne. Similarly, the larvae of the ophidiid genus Luciobrotula have been tentatively identified since 1988, with posteriorly displaced dorsal fins and bulging or exterilium guts. However, neither of these larval forms morphologically agree with their adult counterparts. Recently, blackwater divers captured and photographed specimens of larval Luciobrotula and Pycnocraspedum off the coast of Hawaiʻi and Florida, making them available for both morphological and molecular sampling. After examining these larvae and analyzing DNA barcode sequences, as well as a newly captured and sequenced adult of Pycnocraspedum phyllosoma, we revise the previously identified "Pycnocraspedum" larvae to species of Luciobrotula. We describe the larvae of Luciobrotula bartschi and Luciobrotula corethromycter for the first time, highlighting an extraordinary loss of multiple anterior dorsal-fin elements in their ontogeny. We also generate the first DNA sequences for L. corethromycter and P. phyllosoma, adding to the depauperate number of sequences available for ophidiiforms. For the previously identified "Luciobrotula" larvae, neither morphological nor molecular characters provide definitive identification other than recovering them among the Bythitidae. We provide new morphological observations, revised descriptions, and generate a phylogeny of ophidiiform fishes based on COI to place these larvae in a phylogenetic context, prompting further investigation into the relationships of the Ophidiiformes using additional genetic markers. Our study emphasizes the importance of blackwater diving to improving our understanding of marine larval fishes and the need for additional molecular sampling of the diverse order of brotulas, cusk-eels, pearlfishes, and their allies. [ABSTRACT FROM AUTHOR]

This work aims to describe the larval stages and the seasonal variation in the abundance of three mesopelagic species whose larvae are surprisingly abundant near coral reef areas in the Red Sea. The larvae were collected monthly using a plankton net (500 µ) from three coastal coral reef areas surrounding Sharm El-Sheikh on the Egyptian Red Sea coast between January and December 2015. The identification of larvae was based on the morphological and meristic characteristics according to the available literature. The larvae of this species were divided into preflexion, flexion, and postflexion stages and they were also categorized according to their size into relevant size classes. Mesopelagic fishes were represented in the collection by four species belonging to four families: Vinciguerria mabahiss (Family: Phosichthyidae), Benthosema pterotum (Family: Myctophidae), Astronesthes martensii (Family: Stomiidae; subfamily: Astronesthinae), and Trichiurus sp. (Family: Trichiuridae). In general, a total of 3678 larvae were collected, of which 1191, constituting about 32% of the total fish larvae, belonged to mesopelagic species. The most abundant species was V. mabahiss, with 677 larvae that constituted 18% and 57% of the total larvae and mesopelagic fish larvae, respectively. The second most abundant species was B. pterotum, which was represented by 485 larvae (13% of the total larvae and 40% of the mesopelagic fish larvae). A. martensii was represented by the lowest number of larvae (29 larvae, 2%). Most larvae of the three species were small and in the preflexion stage, whereas larger larvae are absent. They are highly abundant in the cooler months of the year between November and April. The high number of preflexion larvae may indicate that the three mesopelagic species spawn in the colder times of the year. [ABSTRACT FROM AUTHOR]

Coastal habitats play a key role in the early life stages of flatfish species, with the quantity and quality of the food they supply being central. However, survival and sufficient development until metamorphosis depend upon obtaining certain essential long-chain polyunsaturated fatty acids (LC-PUFAs). We focused this literature review on flatfish requirements, supplies and availability of three most important LC-PUFAs: DHA (docosahexaenoic acid; 22:6n-3), EPA (eicosapentaenoic acid; 20:5n-3) and ARA (arachidonic acid; 20:4n-6). First, based on aquaculture research, we summarize their importance for larval development and highlight that Solea spp. are the only marine flatfish known to synthesize DHA, which influences their LC-PUFA requirements. Second, analysis of published LC-PUFA contents in the flatfish larvae prey indicates that they most likely cannot synthesize essential LC-PUFA. They show large differences in DHA and EPA content between species, study sites, feeding environments and developmental stages. Third, LC-PUFA contents of phytoplankton, as the main source of essential LC-PUFAs for the prey of flatfish larvae, vary with species, seasons, nutrient availabilities and temperature. However, flatfish larvae prey probably overcome some limiting conditions by targeting species with high LC-PUFA contents through preferential assimilation and/or selective feeding on prey quality as done by flatfish larvae at a higher trophic level. Fourth, in the scarcity of available data, we propose future research avenues. One of them could investigate relations between availability of LC-PUFAs and plankton biodiversity, which appears to be key in meeting flatfish larvae requirements in coastal habitats and may be influenced by the current increasing human pressure. [ABSTRACT FROM AUTHOR]

There were two stocking densities (i.e. 9,000 and 12,000 larvae m−2), two doses of 17β-estradiol and control without any hormonal treatment i.e. 0, 2.5, and 5 mg L−1. Hormone were given by immersing larvae in water for six hours to reduce cannibalism in African catfish larvae. Fishes were reared for 14 days intensively. The highest fish survival was at a stocking density of 12,000 larvae m−2 with 2.5 mg L−1 17β-estradiol. Cannibalism decreased at higher densities compared to the control. The level of 17β-estradiol in treated fish tended to be higher than that of the control group but the coefficient of variance decreased. At the end of rearing, the use of 17β-estradiol at higher densities improved the specific growth rate and relative body length. [ABSTRACT FROM AUTHOR]

Objective: A small‐scale culture system effective in producing larvae of endangered Delta Smelt Hypomesus transpacificus was recently developed to facilitate conservation and research efforts. Methods: To optimize its use, we examined the effect of stocking density (300, 500, 700, and 900 fish per 92 L of water) on the length, weight, and survival of late‐stage larvae (41 days posthatch) reared for 40 days in the small‐scale system. Result: Stocking density had no effect on larval survival or size. Also, the survival, length, and weight of these fish did not differ from those reared using standard, large‐scale culture practices (2500 fish per 320 L of water). Conclusion: Our findings validate the methods used for small‐scale Delta Smelt rearing, help optimize these protocols, and thereby enhance Delta Smelt rearing capabilities needed for research and conservation. Impact statementThis study optimizes and validates use of a new culture system for rearing a specific life stage of Delta Smelt. In doing so, we enhance ongoing conservation efforts to prevent the extinction of this endangered species. [ABSTRACT FROM AUTHOR]

Marine larvae must sense various environmental cues to find a suitable spot where they can settle and metamorphose. New work identifies the specific neurons that transduce these cues in the larva of Ciona , a non-vertebrate chordate. [ABSTRACT FROM AUTHOR]

Mortality rates of marine fish larvae are incredibly high and can determine year‐class strength. The major causes of larval mortality are predation and starvation, and the performance of larvae in survival skills that can mitigate this mortality (predator evasion, foraging) varies among individuals and cohorts, but the causes of the variation are not known. Transcriptomics can link gene expression variation to phenotypic variation at the whole‐system level to investigate the molecular basis of behavioural variation. We used tag‐based RNA‐sequencing to examine the molecular basis of variation in predator evasion and routine swimming (trait related to foraging efficiency) in the larval red drum, Sciaenops ocellatus. We looked for functional gene networks in which interindividual variation would explain variation in larval behavioural performance. We identified co‐expressed gene groups ("modules") associated with predator evasion traits and found enrichment of motor, neural and energy metabolism pathways. These functional associations and pattern of correlations between modules and traits suggest that energy availability and allocation were responsible for the magnitude of startle responses, while differential neural and motor activation were associated with differences in response latency. [ABSTRACT FROM AUTHOR]

The environmental heterogeneity of the biotopes that compound the mosaic of the rivers is essential for the development of the initial stages of fish life. In this sense, we evaluated the abundance and composition of ichthyoplankton community from different biotopes of the Ibicuí River and its relation with environmental variables, between October 2019 and January 2020. The ichthyoplankton sampling was performed in the Ibicuí River basin, in four biotopes: main river (Ibicuí River), tributary river (Ibirocá River), mouth and lake. Larvae from twenty-nine species were identified, including some threatened with extinction. Eggs and larvae were found in all biotopes, however eggs were more abundant in the main river and larvae in the lake. This last biotope was characterized by the greater presence of larvae in the post-flexion stage and sedentary species. The tributary river had a greater presence of larvae of migratory species. Eggs and yolk-sac larvae were positively correlated with the water speed and river width, while the most developed larvae were correlated with electrical conductivity and zooplankton. Our study revealed that the abundance and diversity of the ichthyoplankton were heterogeneously distributed among the biotopes, where hydrogeomorphological and limnological characteristics enable the emergence of distinct ichthyoplankton assemblages along the river gradient. [ABSTRACT FROM AUTHOR]

The larval and post-larval forms of many marine organisms, such as oysters, crabs, lobster, coral, and fish, utilize ambient acoustic cues to orient, settle, or metamorphose. In this study, the effect of anthropogenic and ambient sounds on the orientation behavior of four larval estuarine fishes was examined in a controlled, laboratory experiment. Pre-settlement size red drum Sciaenops ocellatus, southern flounder Paralichthys lethostigma, spotted seatrout Cynoscion nebulosus, and Florida blenny Chasmodes saburrae larvae were exposed to four sound treatments—control, estuarine soundscape, seismic airguns, and large-ship passage—in a linear acoustic chamber. Initial significant (p < 0.05) avoidance of airguns was observed in three of the four species (all but the Florida blenny), but habituation to this sound occurred as the experiment progressed. All species avoided ship passage sounds; however, the avoidance behavior was not significant. Interestingly, none of the species studied were significantly attracted to the acoustic cues alone of the estuarine soundscape; in fact, three of the four species spent less time near the speaker when it was broadcast. These results suggest that larval fish can potentially habituate to anthropogenic noise relatively quickly (<10 min). Understanding how sounds affect larval behavior is necessary because successful recruitment ultimately affects a population's success. [ABSTRACT FROM AUTHOR]

Simple Summary: Microplastics (MPs) contamination is a worldwide problem. Studies have also demonstrated their presence in fish feed, posing serious issues for the aquaculture sector. The present study investigated, for the first time through a comparative approach, the effects of different-sized fluorescent MPs included in a diet intended for zebrafish (Danio rerio). A comparison based on fish developmental stage (larval vs. juvenile), exposure time, and dietary MPs' size and concentration was performed, applying a set of laboratory analyses to elucidate MPs' possible effects on fish growth and welfare, translocation among tissues and organs, and the presence of biological barriers capable of trapping MPs. Results showed that smaller MPs and longer dietary exposure are responsible for translocation of MPs from the gut to other tissues and organs. However, the biological barriers of zebrafish are able to limit MPs' translocation to the muscle. Results obtained in this experimental model are important for possible application to other farmed finfish species. One of the main sources of MPs contamination in fish farms is aquafeed. The present study investigated, for the first time through a comparative approach, the effects of different-sized fluorescent MPs included in a diet intended for zebrafish (Danio rerio). A comparison based on fish developmental stage (larval vs. juvenile), exposure time, and dietary MPs' size and concentration was performed. Four experimental diets were formulated, starting from the control, by adding fluorescent polymer A (size range 1–5 µm) and B (size range 40–47 µm) at two different concentrations (50 and 500 mg/kg). Zebrafish were sampled at 20 (larval phase) and 60 dpf (juvenile stage). Whole larvae, intestine, liver and muscles of juveniles were collected for the analyses. Polymer A was absorbed at the intestinal level in both larvae and juveniles, while it was evidenced at the hepatic and muscular levels only in juveniles. Hepatic accumulation caused an increase in oxidative stress markers in juveniles, but at the same time significantly reduced the number of MPs able to reach the muscle, representing an efficient barrier against the spread of MPs. Polymer B simply transited through the gut, causing an abrasive effect and an increase in goblet cell abundance in both stages. [ABSTRACT FROM AUTHOR]

Amazonian blackwaters are extremely biodiverse systems containing some of Earth's most naturally acidic, dissolved organic carbon -rich and ion‐poor waters. Physiological adaptations of fish facing these ionoregulatory challenges are unresolved but could involve microbially-mediated processes. Here, we characterize the physiological response of 964 fish-microbe systems from four blackwater Teleost species along a natural hydrochemical gradient, using dual RNA-Seq and 16 S rRNA of gill samples. We find that host transcriptional responses to blackwaters are species-specific, but occasionally include the overexpression of Toll-receptors and integrins associated to interkingdom communication. Blackwater gill microbiomes are characterized by a transcriptionally-active betaproteobacterial cluster potentially interfering with epithelial permeability. We explore further blackwater fish-microbe interactions by analyzing transcriptomes of axenic zebrafish larvae exposed to sterile, non-sterile and inverted (non-native bacterioplankton) blackwater. We find that axenic zebrafish survive poorly when exposed to sterile/inverted blackwater. Overall, our results suggest a critical role for endogenous symbionts in blackwater fish physiology. Amazonian blackwaters are acidic and physiologically-challenging, but are one of Earth's most diversified ecosystems. This study revealed that fish survival in these hostile habitats depends on the colonization of their gills by endogenous blackwater Betaproteobacteria, with the potential to regulate host ionoregulatory processes. [ABSTRACT FROM AUTHOR]

Eastern boundary systems support major fisheries of species whose early stages depend on upwelling production. However, upwelling can be highly variable at the regional scale, leading to complex patterns of feeding, growth, and survival for taxa that are broadly distributed in space and time. The northern California Current (NCC) is characterized by latitudinal variability in the seasonality and intensity of coastal upwelling. We examined the diet and larval growth of a dominant myctophid (Stenobrachius leucopsarus) in the context of their prey and predators in distinct NCC upwelling regimes. Larvae exhibited significant differences in diet and growth, with greater seasonal than latitudinal variability. In winter, during reduced upwelling, growth was substantially slower, guts less full, and diets dominated by copepod nauplii. During summer upwelling, faster-growing larvae had guts that were more full from feeding on calanoid copepods and relying less heavily on lower trophic level prey. Yet, our findings revealed a dome-shaped relationship with the fastest growth occurring at moderate upwelling intensity. High zooplanktivorous predation pressure led to above average growth, which may indicate the selective loss of slower-growing larvae. Our results suggest that species whose spatio-temporal distributions encompass multiple regional upwelling regimes experience unique feeding and predation environments throughout their range with implications for larval survivorship. [ABSTRACT FROM AUTHOR]

The freshwater angelfish (Pterophyllum scalare) is a quite popular freshwater ornamental fish in Indonesia due to its distinguished body shape and pattern. However, its growth tends to be slow due to low nutrients in its main diet, namely Daphnia magna. The most feasible solution is to enrich D. magna to increase its nutritional content with Viterna (livestock vitamins). The purpose of this study was to determine the effectiveness of D. magna enriched with Viterna to increase the growth of freshwater angelfish. This study used a Completely Randomized Design to compare three enrichment dosages (10, 20, and 30 ml/L) with a non-enriched control in three replications. This study showed that 3 hours-enrichment can result in an increase in fat (0.6%) and protein (1.25%) profiles in D. magna. Absolute Weight Growth (AWG), Absolute Length Growth (ALG), and Specific Growth Rates (SGR) showed significant differences (P=0.05) between all treatments. The best result was obtained at a Viterna dosage of 30 ml/L which resulted in an Absolute Weight Growth value of 207.14 mg, an Absolute Length Growth of 14.19 mm, and an SGR of 2.58%/day. Survival rates during the larvae culture were not statistically different (P=0.05) among the treatments. Enrichment of D. magna with Viterna has been proven to optimize its potential as live food for fish larvae cultivation. [ABSTRACT FROM AUTHOR]

Microplastics (MPs) are emergent pollutants in freshwater environments and may impact aquatic organisms, including those of nutritional value. The specific activities of digestive and antioxidant enzymes can be used as good bioindicators of the potential effects of MPs on fish in case of waterborne MP contamination. In this study, we used fluorescent polystyrene microplastics (PS-MPs) to analyze the alterations in enzyme activities in larvae of Coregonus peled Gmelin (peled or Northern whitefish), one of the most valuable commercial fish species of Siberia. Our results indicate that peled larvae can ingest 2 µm PS microspheres in a waterborne exposure model. A positive correlation (rs = 0.956; p < 0.01) was found between MP concentration in water and the number of PS microspheres in fish guts, with no significant differences between 24 h and 6-day exposure groups. The ingestion of MPs caused alterations in digestive enzyme activity and antioxidant responses at the whole-body level. The presence of PS-MPs significantly stimulated (p < 0.05) the specific activity of α-Amylase and non-specific esterases in peled larvae after 24 h. However, a pronounced positive effect (p < 0.05) of MPs on the activity of pancreatic trypsine and bile salt-activated lipase was only found after 6 days of exposure compared to after 24 h. Intestinal membrane enzyme aminopeptidase N was also stimulated in the presence of PS-MPs after 6-day exposure. We also observed a significant increase in the specific activity of catalase in peled larvae after 6 days of exposure, which indicates the MP-induced modulation of oxidative stress. Taken together, these results highlight the potential impact of environmental MPs on northern commercial fish, their importance for estimating fish stocks, and the sustainability of freshwater ecosystems. [ABSTRACT FROM AUTHOR]

Omnipresent microplastics (MPs) in marine ecosystems are ingested at all trophic levels and may be a vector for the transfer of persistent organic pollutants (POPs) through the food web. We fed rotifers polyethylene MPs (1–4 µm) spiked with seven congeners of polychlorinated biphenyls (PCBs) and two congeners of polybrominated diphenyl ethers (PBDEs). In turn, these rotifers were fed to cod larvae from 2–30 days post-hatching (dph), while the control groups were fed rotifers without MPs. After 30 dph, all the groups were fed the same feed without MPs. Whole-body larvae were sampled at 30 and 60 dph, and four months later the skin of 10 g juveniles was sampled. The PCBs and PBDEs concentrations were significantly higher in MP larvae compared to the control larvae at 30 dph, but the significance dissipated at 60 dph. Expression of stress-related genes in cod larvae at 30 and 60 dph showed inconclusive minor random effects. The skin of MP juveniles showed disrupted epithelial integrity, fewer club cells and downregulation of a suite of genes involved in immunity, metabolism and the development of skin. Our study showed that POPs were transferred through the food web and accumulated in the larvae, but that the level of pollutants decreased once the exposure was ceased, possibly related to growth dilution. Considering the transcriptomic and histological findings, POPs spiked to MPs and/or MPs themselves may have long-term effects in the skin barrier defense system, immune response and epithelium integrity, which may potentially reduce the robustness and overall fitness of the fish. [ABSTRACT FROM AUTHOR]