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During fish larvae development functional, morphological, and physiological adaptations are key in larval survival strategies and can determine mortality bottlenecks. For many fish groups such as needlefish, which play crucial roles in marine food webs, studies on early life stages are almost lacking. Herein, the development, with focus on the postcranial skeleton, of the garfish Belone belone (Linnaeus, 1761) is described and a staging system is introduced. Ten larval and juvenile life stages are proposed in three main phases: yolk sac, larval, and juvenile development. During the yolk sac phase the garfish deplete their yolk reservoirs and finish the development of their unpaired fins. During the larval period the lower jaw elongates and the needlenose stage is reached. In the juvenile phase, the upper jaw elongates until both jaws are almost equally long. Since B. belone larvae develop much of their postcranial skeleton in the late embryonic and yolk sac phases they might not experience a severe bottleneck in this early stage such as many other marine fish species. Therefore, young garfish could be more resilient to environmental changes. [ABSTRACT FROM AUTHOR]

As ecosystems change, understanding the consequences for fish population dynamics and habitat use is essential for resource management. Using white perch (Morone americana) survey data on early life stages collected during a long-term ichthyoplankton monitoring program in the Hudson River (New York, USA), an ecosystem under immense pressure from climate change, ecological shifts, and anthropogenic activities, we evaluated the drivers of changes in egg abundance and spawning habitat between 1980 and 2017. Results indicated that egg abundance is associated nonlinearly with temperature, conductivity, discharge, depth, location, and the week of year. We also found that egg abundance has declined within the river over time. Additionally, shifts in hotspots of spawning activity were identified, including evidence that the lower extent of spawning habitat has moved upriver since 1980. This study indicates that the dynamics of white perch early life histories and spawning habitat are changing. It also highlights the utility of a long-term monitoring program for broadening our understanding of fish ecology in the age of big data in changing ecosystems. [ABSTRACT FROM AUTHOR]

As a carnivorous fish, the cannibalism are prone to happen in the early seedling stage in Dongting catfish (Silurus asotus), especailly when there is not enough food, which resulting in the low survival rate of Dongting catfish. To find clues to improve the survival rate of Dongting catfish offspring, the comparative transcriptomics analysis were conducted between normal and malformed larval fish, as well as normal larval fish before and after first food intake. In normal and malformed larval fish groups, a total of 881 differential genes were identified, including 634 up-regulated genes and 247 down-regulated genes. From these genes related to growth hormone synthesis and secretion were screened out as SLA isoform X1, SOCS3, STAT1b, JUNB, respectively. In the group of larval fish before and after the first food intake, 4901 up-regulated genes and 3660 down-regulated genes were found, from which the differential genes related to protein digestion and absorption pathway and pancreatic secretion pathway were screened out as cathepsin D precursor, elastase 2 like precursor, elastase 2 precursor, LPL isoform X1, CTRB1 precursor, CTRL precursor, CPA precursor, FABP, SLC15A1, CEL tandem duplicate 2 precursor. The differential genes screened for association with amino acid metabolism were ASAOC precursor, PLD3, NDPKs, trehalase, UMP-CMP kinase, L-amino-acid oxidase, PLB1, FALDH isoform X2, PLA2 precursor, glucokinase. Mean while, nine differential genes were selected for qPCR verification. The results confirmed that the relative expression trends of these genes were consistent with those found in the transcriptome. These findings provide an important reference for developing strategies to enhance the survival rate of Dongting catfish at early seedling stage. [ABSTRACT FROM AUTHOR]

Nutritional programming is a promising concept for promoting metabolic adaptation of fish to challenging conditions, such as the increase in water temperature. The present work evaluates in ovo arginine or glutamine supplementation as enhancers of zebrafish metabolic or absorptive capacity, respectively, at optimum (28 ºC) and challenging temperatures (32 ºC) in the long-term. Growth performance, free amino acids profile, methylation index and the activity levels of digestive and intermediary metabolism enzymes were analysed to assess the metabolic plasticity induced by an early nutritional intervention. Temperature affected fish larvae growth performance. At the end of the experimental period 28 ºC-fish showed higher dry weight than 32 ºC-fish. The effects of the early supplementation were reflected in the larval free amino acids profile at the end of the experiment. Higher methylation potential was observed in the ARG-fish. In ovo amino acid supplementation modulated the metabolic response in zebrafish larvae, however, the magnitude of this effect differed according to the amino acid and the temperature. Overall, arginine supplementation enhanced carbohydrates metabolism at 32 ºC. In conclusion, the present work suggests that in ovo arginine supplementation may promote a better adaptive response to higher temperatures. [ABSTRACT FROM AUTHOR]

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Linking habitat availability with hydraulic models integrates river engineering in the ecological field. Field observation for species presence and physical habitat availability mapping is inherently limited due to time and access constraints for field data collection. This study leverages hydraulic modeling to supplement larval fish population monitoring data, effectively expanding mapped physical habitat and allowing for monitoring bias analysis. The inundation extents and character of streamflow from hydraulic modeling were used to refine habitat suitability indices relative to total habitat availability from discrete fish monitoring events. Given the flexibility in hydraulic modeling to simulate a range of flows, the habitat suitability index is then translated to an effective habitat curve according to areal inundation and hydrologic frequency. With this framework, forecasting the impacts of long‐term trends, such as geomorphic or hydrologic change, can be reasonably and quantitatively assessed. This manuscript uses a case study of Rio Grande silvery minnow monitoring at restoration sites where the floodplain has been lowered via earthwork. Comparisons are made for habitat suitability indices developed from field observation data alone and field observation supplemented by hydraulic modeling. Known biases of field sampling data (targeting slow, shallow areas where fish are most often found) were confirmed based on simulated hydraulic conditions across entire restoration sites. In the case of Rio Grande silvery minnow, a heavily studied species, such field monitoring biases are an effective use of resources. However, this framework may be helpful for assessing alternative management approaches and monitoring strategies of species that are less studied. [ABSTRACT FROM AUTHOR]

Temperature and nutrition are suggested as the primary factors affecting larval survival during the transition from endogenous to exogenous feeding in fish. However, little is known about its simultaneous impact during this period. In this study, Seriola rivoliana eggs were subjected to a constant 24 °C (CTE) and a daily temperature fluctuation (DTF) between 22.8 and 25.2 °C until oil droplet exhaustion (5.5 days after hatching). On the other hand, marine fish larvae mostly rely on live feed, with certain nutritional deficiencies such as poor long-chain fatty acids. Thus, rotifer Brachionus rotundiformis enrichment was simultaneously evaluated with temperature using three enrichment diets: Ori-green, S.presso, and a Domestic emulsion. For this purpose, the five experimental groups were established in triplicate using six 100-L tanks with three 10-L containers inside (18 experimental units in total). One hundred eggs were incubated, using a green water system, and 10 rotifers mL−1 were offered at mouth opening. After oil droplet exhaustion, survival was only affected by temperature (P < 0.01), being higher at DTF compared to CTE. At the same stage, Domestic emulsion resulted in bigger larvae than Ori-green. In a further assay at 3.7 DAH, the relative expression of the trypsin gene was higher at Domestic emulsion compared to S.presso and Ori-green. This study indicates that daily temperature fluctuation can improve larval performance and low levels of EPA and DHA in Domestic emulsion enriched rotifers were not critical for Seriola rivoliana at first feeding. [ABSTRACT FROM AUTHOR]

Pufferfish of the genus Takifugu possess tetrodotoxin (TTX), known as "pufferfish toxin" and it is believed that pufferfish eggs and newly hatched larvae utilize TTX as a defensive substance against predators. However, the mechanism for the placement of TTX to specific cells on the larval body surface during the developmental process remains unknown. In this study, we clarify the distribution and characteristics of TTX-rich cells. We performed whole-mount immunohistochemistry (IHC) using anti-TTX monoclonal antibody on larvae of two pufferfish species, Takifugu rubripes and Takifugu alboplumbeus, just after hatching. This allowed observation of the TTX location and compared it with those of wheat germ agglutinin (WGA)-positive (periodic acid-Schiff (PAS)-positive) cells for mucous cells and IHC using anti-Na+/K+-ATPase (NKA) monoclonal antibody for ionocytes. As a result, uniformly scattered localization of TTX-rich cells was commonly observed in the epidermis of the larvae of the two Takifugu species. TTX-rich cells were WGA-negative (PAS-negative) and structurally distinct from NKA-positive cells, suggesting that TTX-rich cells are unreported small cells unique to pufferfish skin, but not mucous cells nor ionocytes. [ABSTRACT FROM AUTHOR]

ABSTRACT The distribution of fish larvae and other planktonic organisms is highly heterogenous and influenced by a complex interplay of physical, behavioural and ecological processes operating across different scales. Information on patterns and scale of resulting patchiness in plankton distributions is pivotal for understanding the bio‐physical linkages, trophodynamics and ecological strategies in the marine pelagic environment. In this study, we examine the distribution and degree of patchiness of four fish larvae species and their copepod prey, placing specific emphasis on the scale of patterns in both horizontal and vertical dimensions. Our sampling effort encompassed a 120 km long transect of stations covering a frontal area in the southern North Sea, employing depth‐stratified net sampling at varying station distances. Our results show distinct distributional patterns and migratory behaviours among different taxa of both larvae and their copepod prey, yet some commonalities were apparent. Across all species, we observed increased patchiness at larger spatial scales, significantly influenced by day/night fluctuations and hydrography. The overall findings highlight the dynamic nature of patch distributions and underscore the strong impact of hydrographic interfaces, whether vertically oriented pycnoclines or horizontally structured hydrographic fronts. These insights into bio‐physical linkages deepen our understanding of the mechanisms driving larval survival, prey availability and overall ecosystem dynamics. [ABSTRACT FROM AUTHOR]

Long-term datasets provide context and understanding of complex ecological processes, including temporal variations in species diversity and ecosystem dynamics. This dataset is comprised of body length measurements (mm) of more than 380,000 larval or juvenile fish of 30 species from five English river catchments collected almost monthly over two decades. Such information can be used to determine growth rates, future recruitment success, population structure and compliance with monitoring protocols and conservation objectives. The dataset provides a baseline for analysing the impacts of anthropogenic disturbances such as climate change, pollution and habitat degradation, and, given that many fish populations are size structured with a positive relationship between fish body length and various biological attributes such as swimming ability, survival and fecundity, it will be invaluable for investigating natural and human- induced disturbances. [ABSTRACT FROM AUTHOR]

Most teleost fish propel themselves with lateral body waves powered by their axial muscles. These muscles also power suction feeding through rapid expansion of the mouth cavity. They consist of muscle segments (myomeres), separated by connective tissue sheets (myosepts). In adult teleosts, the fast axial muscle fibres follow pseudo‐helical trajectories, which are thought to distribute strain (relative fibre length change) approximately evenly across transverse sections during swimming, thereby optimizing power generation. To achieve strain equalization, a significant angle to the longitudinal axis on the frontal plane (azimuth) is necessary near the medial plane, increasing strain. Additionally, a deviation from longitudinal orientation on the sagittal plane (elevation) is required laterally to decrease strain. Despite several detailed morphological studies, our understanding of muscle‐fibre orientations in the entire axial musculature of fish remains incomplete. Furthermore, most research has been done in post‐larval stages, leaving a knowledge gap regarding the changing axial muscle architecture during larval development. Larval fish exhibit different body size, body shape and swimming kinematics compared to adults. They experience relatively high viscous forces, requiring higher tail‐beat amplitudes to overcome increased drag. Additionally, larval fish swim with higher tail‐beat frequencies. Histological studies have shown that in larval fish, muscle fibres in the anal region transition from an almost longitudinal orientation to a pseudo‐helical pattern by 3 dpf (days post‐fertilization). However, these studies were limited to a few sections of the body and were prone to shrinkage and tissue damage. Here, we introduce a novel methodology for quantifying muscle‐fibre orientations along the entire axial muscles. We selected 4 dpf larval zebrafish for our analyses, a stage where larvae are actively swimming but not yet free‐feeding. High‐resolution confocal 3D scans were obtained from four genetically modified zebrafish expressing green fluorescent protein in fast muscle fibres. Fluorescence variation allowed segmentation of individual muscle fibres, which were then converted to fish‐bound coordinates by correcting for the fish's position and orientation in the scan, and normalized to pool results across individuals. We show that at 4 dpf, muscle‐fibre trajectories exhibit a helical pattern tapering towards the tail. Average fibre angles decrease from anterior to posterior, with azimuth varying over the dorsoventral axis and elevation varying over the mediolateral axis. Notably, only the anteriormost 20% of the body displayed higher azimuth angles near the medial plane. Angles between neighbouring fibres were substantial, particularly at the rim of the epaxial and hypaxial muscles. The revealed muscle‐fibre architecture at this age presumably contributes to the swimming performance of these larvae, but that swimming performance is probably not the only driving factor for the fibre pattern. Our methodology offers a promising avenue for exploring muscle‐fibre orientations across ontogenetic series and provides a foundation for in‐depth functional studies on the role of muscle architecture in facilitating swimming performance of larval fish. [ABSTRACT FROM AUTHOR]

Diuron (3-(3,4-dichlorophenyl)-1,1-dimethylurea) is an herbicide used in many crops, including sugar cane cultivation. It is commonly found in aquatic ecosystem and is of high concern due to its ability to persist in the environment. Diuron metabolites include DCA (3,4-dichloroaniline) and DCPMU (3-(3,4-dichlorophenyl-1-methylurea). The objective of this study was to evaluate the effects of diuron and two of its metabolites in zebrafish (Danio rerio) developing embryos, from biochemical to individual level. Activities of the enzymes acetylcholinesterase (AChE), catalase (CAT), glutathione-S-transferase (GST), and lactate dehydrogenase (LDH) and the levels of lipid peroxidation (LPO), swimming activity, and body length were investigated after an exposure of 120 h, and the heart rate was determined after 48 h of exposure. The range of concentrations tested was 0.003–3.000 mg/L diuron, 0.020–1.500 mg/L DCA, and 0.020–2.100 mg/L DCPMU. Results showed that AChE activity was inhibited by diuron (3.000 mg/L) and DCPMU (0.326, 0.828 mg/L). However, the swimming activity of fish larvae exposed to diuron or its metabolites was not affected. The CAT was induced by DCPMU, and GST was induced by diuron. This suggests that CAT is acting to cope with oxidative stress induced by DCPMU and GST might have a role in the detoxification of diuron. In addition, larvae exposed to DCA (0.633 and 1.500 mg/L) had a reduction in their length, and larvae exposed to diuron (0.754 and 3.000 mg/L) and DCA (0.267, 0.633, and 1.500 mg/L) presented bradycardia, suggesting cardiotoxicity. Overall, results indicate that diuron, DCA, or DCPMU induces adverse effects during the early phases of zebrafish development, such as the impairment of neurotransmission and cardiovascular function and alterations in antioxidant enzymes and growth. Diuron appeared as more toxic than its metabolites since the lowest LOEC (0.012 mg/L) and higher integrated biomarker response (IBR) values were obtained with exposure to this herbicide. Furthermore, as it is fast degraded into DCA and DCPMU, which also affected the zebrafish developing embryos at environmentally relevant concentrations, its use might be of concern in ecosystems that receive agriculture runoff due to their potential adverse effects to aquatic biota. [ABSTRACT FROM AUTHOR]

ABSTRACT Anisakis simplex larvae, commonly found in marine fish, cause anisakiasis in humans, resulting in gastric to gastro‐allergic symptoms. Despite known health risks, the impact of Anisakidae larvae on fish hosts is less understood. This study aimed to investigate this interaction by assessing the feeding strategy of A. simplex. Anisakis larvae were isolated from North Sea Merluccius merluccius tissues (stomach, body cavity, liver and muscle) and were analysed for carbon (δ13C) and nitrogen (δ15N) isotope values. Significant differences in δ13C values were found among host tissues, with the liver differing from muscle and stomach tissues. In contrast, no differences were noted for the associated parasites. Additionally, δ15N values indicated that the host occupied a significantly higher relative trophic position than its parasite. This suggests a lack of direct nutrient transfer from host to parasite, as the parasite would typically exhibit higher stable isotope values than the tissue they feed on. Therefore, A. simplex's stable isotope values might reflect those of its previous host (crustacean and/or small fish), providing insights into diet and movement of the paratenic M. merluccius host. Further research is needed to confirm these findings across different fish species and to explore A. simplex as a proxy for trophic ecology. [ABSTRACT FROM AUTHOR]

To describe the species composition of fish larvae and juveniles in the Nanji Islands, monthly collection was conducted at 12 stations around the Nanji Islands from March 2023 to February 2024 by using horizontal tow at the surface layer. The fish larvae and juveniles were collected by a larva net (1.3 m mouth diameter, 0.5 mm mesh aperture). A total of 6446 fish larvae and juveniles were collected, belonging to 59 species and 54 genera in 11 families. Most of them were preflexion larvae (93.31%). Gobiidae, with eight species, was the most diverse family. Based on the index of relative importance (IRI) result, the dominant species was Sebastiscus marmoratus (Cuvier, 1829), accounting for 84.52% of the total number of samples collected. The common species were Stolephorus commersonii Lacepède, 1803; Omobranchus elegans (Steindachner, 1876); Nibea albiflora (Richardson, 1846); Parablennius yatabei (Jordan & Snyder, 1900); Lateolabrax maculatus (McClelland, 1844); and Odontamblyopus lacepediiand (Temminck & Schlegel, 1845). Other species were all rare species. The highest species number was in September (18 species), and the highest density was in December. Only one fish larva was collected in April. Pielou's evenness index was highest in November, while Margalef's richness index and Shannon–Wiener diversity were highest in September. The result of cluster analysis showed that the 11 months (except April) could be divided into four groups. The species number, density, and three diversity indexes showed no significant correlation with temperature and salinity. [ABSTRACT FROM AUTHOR]

The ratio of mortality to growth of larval fish provides a metric of a cohort's "recruitment potential". Estimating recruitment potential is arduous, requiring growth and mortality to be estimated independently. Here, we propose using the exponent of size spectrum models to indicate recruitment potential from body measurement data alone. This approach has several advantages including (1) reducing data collection times, (2) removing uncertainty in estimates generated from age estimation, and (3) allowing re-analysis of larval fish databases or archived collections. To test the validity of this approach, we conduct simulations comparing estimates of recruitment potential from an abundance spectrum model with other common methods. By varying larval flux rates, growth, mortality, and measurement error, we show the abundance spectrum model is more accurate and precise at smaller sample sizes, and more robust to variance in individual rates and measurement error of ages, but more susceptible to measurement error of size. We highlight that a size-based approach to estimating recruitment potential provides another useful tool for understanding larval survival, reducing resource demands on research compared to traditional methods. [ABSTRACT FROM AUTHOR]

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 coevolutionary dynamic of host–parasite associations varies from strictly local adaptations to diffuse guild coevolution. How innate and acquired immune responses modulate host resistance to parasitism and how host specificity and geographic scaling affect the efficacy of host response have consequences for range dynamics and biological invasions.Using reciprocal transplant experiments, we tested whether local or diffuse coevolution shapes host response to parasitism in the host–parasite association between bitterling fishes and larval stages (glochidia) of freshwater mussels from Europe and East Asia.We found that glochidia initially indiscriminately attached to all study host species, but immune responses elicited significant differences in host responses within 24 h of infection, which intensified during glochidial development. European bitterlings were more resistant to European glochidia and Asian bitterlings to Asian glochidia, with the strongest geographic bias in resistance in the Asian bitterling hosts.This finding suggests a strong effect of local adaptation but also indicates the non‐negligible role of coevolutionary hotspots. Low natural glochidia load on bitterling species overall hence arise from competent immune response rather than glochidia avoidance behaviour. Bitterling immune response is primarily innate and not acquired.Overall, our data demonstrate the complex outcome of parasite pressure on the evolution of host resistance, and important role of geographically structured coevolution in shaping host response. [ABSTRACT FROM AUTHOR]

Aim: Many fish species can harbour a wide range of pathogenic agents in their tissues. Of many pathogens, the parasitic nematode of genus Contracaecum, which resides in the tissues of fish species, can results in fish‐borne infections in humans. This study was planned to assess consumers' awareness of fish‐borne zoonoses in the fishing sites of Lake Chamo, Arba Minch, Ethiopia. The study was also aimed at demonstrating the zoonotic nematode, Contracaecum parasites in the Oreochromis niloticus and Lates niloticus fishes collected from Lake Chamo, Arba Minch, Ethiopia. Methods and Results: Assessment of awareness about fish‐borne zoonoses was conducted in randomly selected participants (n = 162) using face‐to‐face interviews via a structured and semi‐structured questionnaire. Besides, 70 fishes (O. niloticus = 35 and L. niloticus = 35) were examined for the presence of larva of Contracaecum and other anisakid genera through standard dissection, pepsin‐hydrochloric acid digestion and microscopic observation. Consumers have inadequate awareness about fish‐borne zoonoses based on the answers they provided to the questions. The majority of respondents (82%) consume raw fish in the area. Of these, a significantly higher proportion were male (p < 0.001), completed their elementary or high school (p = 0.004), Orthodox Christian (p = 0.044), fishermen (p < 0.001) and participants without previous information about fish‐borne zoonoses (p < 0.001). Overall, of examined fishes (n = 70), n = 15 (21.4%, 95% CI, 12.8–33.2) were infected with Contracaecum larva. A significant (p = 0.028) higher infection prevalence was noted in L. niloticus (34.3%, 95% CI, 19.7–52.3) compared to O. niloticus (8.6%, 95% CI, 2.2–24.2). A unit gram addition in the total weight of fish would significantly raise the risk of Contracaecum infection by 1% (p < 0.001). Conclusions: The presence of Contracaecum, a zoonotic nematode in the fishes, which are often preferred by consumers for raw dishes, designates a high risk of possible fish‐borne infections in the area. Thus, providing education and training for fishermen, visitors of the area, and local people who visit the area for fish consumption, it is inevitably important to minimize the risk. Furthermore, health workers should suspect fish‐borne infections, such as anisakidosis in patients who have a history of raw fish consumption in Arba Minch, Ethiopia. [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]

Advection of pelagic fish larvae through ocean currents is a source of dispersal that is known to structure marine populations by directly impacting population success and persistence. To be able to understand fish population dynamics and manage existing fisheries it is therefore of importance to assess the extent of exchange between populations and determine the factors that drive it, which is still a challenge in fisheries research today. In this study, the output of a highresolution basin-scale circulation model is used to calculate the dispersal probability from spawning areas and the remaining Black Sea for a range of commercially important fish such as anchovy, sprat, turbot, red mullet, and bluefish under different environmental conditions. The common trait of many commercially important species in the Black Sea is that they have pelagic larval stages of different time scales which are simulated by tracking virtual drifters in the simulated surface circulation of the Black Sea. Simulation results show that the dynamic current structure of the Black Sea causes low local retention of larvae. During spring and summer lower offshore transport and higher local retention is observed than in fall and winter, which is directly related to the Rim Current strength. The lowest offshore transport is observed on the northern northwestern shelf, the main spawning area for pelagic fish with still 24-32% of larvae transported offshore. Simulations show that pelagic fish species such as anchovy and sprat adopted different reproductive strategies through their species-specific traits. For the summer spawning species anchovy, timing, and location of spawning together with its short pelagic larval stage is shown to enhance retention on the northwestern shelf. Sprat with its long pelagic larval stage and winter spawning is more adapted to high offshore transport, making it unlikely that sprat is recruited to the same area as where it is spawned. This modeling framework provides a basis for investigating recruitment variability of pelagic fish species in the Black Sea specifically considering the impact of climate variability and provides a useful guide to the potential connectivity of marine populations or the spread of invasive pests in the Black Sea. [ABSTRACT FROM AUTHOR]

Several recent high intensity ENSO events have caused strong negative impacts on the adult phases of foundational species in coral reef ecosystems, but comparatively little is known about how climatic variables related to recent ENSOs are impacting the supply of larvae to benthic populations. In marine fishes and invertebrates, reproductive adults and planktonic larvae are generally more sensitive to environmental variability than older, non-reproductive adults. Further, the transport of larvae in ocean currents may also be strongly ENSO dependent. The interactions between the dynamics of larval survivorship and larval transport could lead to population bottlenecks as stronger ENSO events become more common. We tested the predictions of this hypothesis around the Main Hawaiian Islands (MHI) by constructing a correlation matrix of physical and biological time series variables that spanned 11 years (2007–2017) and multiple ENSO events. Our correlation matrix included four types of variables: i. published ENSO indices, ii. satellite-derived sea surface temperature (SST) and chlorophyll variables, iii. abundance and diversity of larval fishes sampled during the late winter spawning season off Oahu, and iv. abundance and diversity of coral reef fish recruits sampled on the western shore of the Big Island of Hawaii. We found that the abundance and diversity of larval fishes was negatively correlated with the Multivariate El Niño Index (MEI), and that larval variables were positively correlated with measures of fall recruitment (September & November), but not correlated with spring-summer recruitment (May & July). In the MHI, SST variables were not correlated with the MEI, but two successive El Niño events of 2014–15 and 2015–2016 were characterized by SST maxima approaching 30°C. Two large pulses of benthic recruitment occurred in the 2009 and 2014 recruitment seasons, with > 8000 recruits observed by divers over the summer and fall months. Both events were characterized by either neutral or negative MEI indices measured during the preceding winter months. These patterns suggest that La Niña and the neutral phases of the ENSO cycle are generally favorable for adult reproduction and larval development in the spring and summer, while El Niño phases may limit recruitment in the late summer and fall. We hypothesize that episodic recruitment during non-El Niño phases is related to favorable survivorship and transport dynamics that are associated with the formation of pairs of anticyclonic and cyclonic eddies on the leeward sides (western shores) of the Main Hawaiian Islands. [ABSTRACT FROM AUTHOR]

Larval and transforming stages of smallscale weakfish Cynoscion microlepidotus (Sciaenidae) are described and illustrated based on samples obtained in three different sites along the Brazilian coast: São Marcos Bay (Maranhão state), Camamu Bay (Bahia state), and the Cananéia‐Iguape Estuarine System (São Paulo state). Identification of early stages of C. microlepidotus was based on meristic counts, such as number of myomeres (22), number of fin spines and rays (dorsal XI, 24, anal II, 9 and pectoral 19), morphological features (presence of supraoccipital crest in larvae from flexion to transformation stages, branched anal fin spines) and pigmentation pattern. Early stages of this species are likely to be confused with Carangidae and Scorpaenidae due to the presence of a supraoccipital crest, and with the Sciaenidae species Stellifer rastrifer, Macrodon atricauda, M. ancylodon, and Isopistus parvipinnis due to branched anal fin elements. However, a distinction can be made when analyzing the set of characters (morphology, morphometry, pigmentation) in relation to the different stages of development. [ABSTRACT FROM AUTHOR]

In 60 days of feeding, a trial was conducted to evaluate the effects on liver, gut histology, and growth performance of using defatted black soldier fly Hermetia illucens (BSF) larvae meal as a fish meal (FM) protein alternative in the diet of Pontastacus leptodactylus. Fish meal protein was replaced with BSF meal protein at 0%, 20%, 40%, 60%, 80%, and 100%. Six hundred crayfish with an initial weight of 0.033 g were randomly divided into 24 experimental groups with four repetitions. There were no significant differences observed in cheliped, molting numbers, or survival rates between the groups (p > .05). However, adding more than 60% BSF to feeds caused pathological findings in the hepatopancreas,and the intestines. The results of this study showed that 40% defatted BSF meal can be used as a protein source replacement for fish meal protein without affecting the survival rate and growth of P. leptodactylus juveniles. [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]

Although zooplankton were extensively studied in the North Sea, knowledge about winter zooplankton assemblages is still scarce, despite potential influence of zooplankton overwintering stocks on seasonal plankton succession and productivity. Furthermore, several economically and ecologically important fish species reproduce during winter contributing to the zooplankton community as passive members (eggs) or predators (larvae). To elucidate on winter zooplankton distribution, abundance and composition in the Southern North Sea and Eastern English Channel, we defined assemblages based on mesozoo- and ichthyoplankton data sampled between January and February 2008 using fuzzy-clustering and indicator species. Mesozoo- and ichthyoplankton (eggs+larvae) were integrated in a common analysis by using a spatial grid adapted to the datasets and defined by means of a geostatistical method developed in agronomics. Potential environmental drivers of assemblage distribution were evaluated by means of GLMM and comparison with data from 2022 facilitated insight about the inter-annual representativeness of the assemblages. Five zooplankton assemblages were found varying with regard to total zooplankton abundance, dominant and indicator taxa. Spatial variability of abiotic (dissolved nutrients, salinity, depth, temperature, organic matter in suspension, chlorophyll a), biotic variables (phyto- and microplankton composition), water masses and fish spawning grounds were revealed as potential drivers of assemblage distribution. Assemblages off the Rhine-Scheldt estuary and in the German Bight harbored the biggest zooplankton overwintering stocks that might influence the grazing pressure on phytoplankton spring production. Assemblages off the Rhine-Scheldt estuary and covering the English Channel and the Southern Bight were found to be of high importance for herring and plaice larvae. Although further analyses suggested inter-annual representativeness of the assemblages found (2008 vs 2022), the assessment of further years would be necessary to account for potential inter-annual variability. Future studies could profit from the assessment of microzooplankton facilitating insight in fish larvae feeding potential and zooplankton overwintering strategies. [ABSTRACT FROM AUTHOR]

Understanding fundamental life history and ecological attributes of declining endemic fishes is essential for developing effective strategies for their conservation and recovery. In the Great Plains and desert rivers of North America, numerous imperiled leuciscids belong to a unique reproductive ecotype with drifting eggs and larvae (pelagophils). Herein, we synthesize three decades of research on the embryology and early life history of Rio Grande Silvery Minnow Hybognathus amarus, a federally endangered member of this ecotype, and explore how our findings can guide management and conservation of these sensitive taxa. We investigated three early developmental aspects of Hybognathus amarus through aquarium and laboratory studies: 1) egg morphology, development, and density, 2) larval development, growth, and behavior, and 3) morphologic and meristic analysis of larvae and early juveniles. Eggs nearly doubled in size at 10 min post-fertilization, were nonadhesive and nearly neutrally buoyant (specific gravity: 1.0011–1.0024), and hatched within 30 hrs in water about 23°C. Recently emerged protolarvae first transformed to mesolarvae after about one week, to metalarvae after about three weeks, and to juveniles after about six weeks at 20–24°C. Based on six candidate models, larval fish development (i.e., from protolarvae to early juveniles) was best explained by a cubic polynomial growth curve. While most protolarvae developed a gas bladder and began to feed within a week, the complete complement of fin rays (i.e., required for proficient swimming) had not fully formed until about one month post-hatching. Early developmental characteristics (e.g., egg specific gravity and larval fin ray formation), combined with river fragmentation, flow regulation, and habitat loss, can profoundly affect the upstream retention and recruitment of Hybognathus amarus and other native pelagophils. Long-term recovery of these highly imperiled species will depend on restoring sufficient seasonal flows, river and floodplain connectivity, and habitat complexity to promote their successful spawning, growth, and survival. [ABSTRACT FROM AUTHOR]

Large dams significantly impact river ecosystems by disrupting connectivity, altering physicochemical variables, and modifying flow regimes. These modifications influence the spatial and temporal dynamics of biological processes and species distributions. While much research has focused on potamodromous species, there remains a gap in understanding the recovery gradients of resident species in dam‐altered rivers. This study examines the responses of larvae of a resident species, the mandarin fish (Siniperca chuatsi), to environmental alterations caused by the Three Gorges Dam (TGD) in the middle reach of the Yangtze River. We hypothesized that larval abundance, feeding, growth, and survival would exhibit longitudinal recovery gradients, improving with the increased distance from the TGD. Our results confirm this hypothesis, showing that larvae further from the TGD exhibited higher abundance, increased feeding intensity, enhanced growth rates, improved survival rate, and earlier peak abundance and hatching dates. Key environmental factors, including water temperature and discharge, increased downstream, while transparency decreased. Major tributary inputs significantly contributed to these recovery gradients. The observed longitudinal gradients in larval attributes mirrored environmental changes, underscoring the TGD impact on population recruitment. These results highlight the broader implications of dam‐induced changes on resident species recruitment, potentially affecting entire fish communities. Our study contributes to understanding the distinct spatial patterns of population trends, providing valuable insights for designing more effective conservation and management practices for resident freshwater fishes in large regulated rivers. [ABSTRACT FROM AUTHOR]

Ichthyoplankton data sets based on collections from estuaries in South Carolina, North Carolina, Virginia, Delaware, and New Jersey and from ocean cruises off the U.S. East Coast were examined to determine spawning locations in the ocean, cross- shelf distributions of larvae, and movements of spot (Leiostomus xanthurus) into estuaries. Spot spawn during fall and winter near the edge of the continental shelf, primarily south of Cape Hatteras in North Carolina. We documented additional spawning of spot north of Cape Hatteras, close to the coast, in summer and fall. Larval and early juvenile spot enter estuaries from November through May in South Carolina and North Carolina and from January through June in Virginia, Delaware, and New Jersey. Numbers of spot per volume of water sampled decreased from south to north among estuaries and in the ocean. Interannual variations in abundance were high, and no long- term trends were determined. Over the decades, median annual lengths of ingressing larval and juvenile spot decreased as annual mean water temperature increased in South Carolina and North Carolina. The timing of ingress was positively correlated with water temperature. Continued increases in water temperature on the East Coast will likely lead to additional changes in oceanic distribution and ingress patterns of spot. Our findings indicate the value of synthesizing information from long- term studies conducted across broad geographic scales. [ABSTRACT FROM AUTHOR]

The fish gill is a multifunctional organ that is important in multiple physiological processes such as gas transfer, ionoregulation, and chemoreception. This characteristic organ of fishes has received much attention, yet an often-overlooked point is that larval fishes in most cases do not have a fully developed gill, and thus larval gills do not function identically as adult gills. In addition, large changes associated with gas exchange and ionoregulation happen in gills during the larval phase, leading to the oxygen and ionoregulatory hypotheses examining the environmental constraint that resulted in the evolution of gills. This review thus focuses exclusively on the larval fish gill of teleosts, summarizing the development of teleost larval fish gills and its function in gas transfer, ionoregulation, and chemoreception, and comparing and contrasting it to adult gills where applicable, while providing some insight into the oxygen vs ionoregulatory hypotheses debate. [ABSTRACT FROM AUTHOR]

The provision of quality and sufficient shrimp fry for production is largely determined by the management of maintenance during larval stadia. This study aims to obtain the best treatment of natural feed in the form of Spirulina sp. and Artemia sp. as feed supplements to improve the growth performance and survival rate of patin fish larvae. The experiment used a Complete Randomized Design consisting of 4 feed treatments and 3 replicates: A (Artemia sp. 100%), B (Artemia sp. 100% and Spirulina sp. 100%), C (Artemia sp. 50% and Spirulina sp. 50%), and D (Spirulina sp. 100%). The larvae with a density of 50 heads/L were kept in the aquarium and fed according to the treatment. The density of Spirulina sp. administered was 104–105 cells/mL maintained until day 7 according to the treatment. The parameters measured included growth performance, which included specific growth rate (SGR), survival (SR), absolute length growth (PPM), and analysis of larval digestive enzymes (amylase, lipase, and protease). The data were analyzed using one way-analysis of variance and continued with Duncan's Multiple Range Test with a 95% confidence interval using SPSS version 22.0. The results showed that the administration of Spirulina sp. produced better SGR, SR, PPM, amylase enzyme, lipase, and protease activities compared to the control (100% administration of Artemia sp.). The best treatment was given by 100% Spirulina sp. treatment. [ABSTRACT FROM AUTHOR]

This article discusses the association between argonauts, a group of octopods, and various substrates in the ocean. The study used images shared by recreational divers on social media to quantify the diversity of substrates used by argonauts for movement. The images showed that argonauts were attached to plastic waste, vegetal debris, and pelagic animals, with gelatinous plankton being the most abundant substrate. The study also observed accompanying fauna sharing the same substrate with the argonauts. The findings highlight the value of citizen science and the use of high-quality images obtained during blackwater dives for studying the behavior and interactions of oceanic pelagic organisms. [Extracted from the article]

For fish oil-free aquafeed development, a photoautotrophic microalga Tisochrysis lutea is believed to be the candidate source of n-3 highly unsaturated fatty acid (n-3 HUFA) because of its docosahexaenoic acid (DHA) biosynthesis. While DHA contents of T. lutea vary during the cultivation periods depending on algal growth phase, little is mentioned about how this dependence should be taken into consideration when evaluating the suitability of microalgae as an alternative to fish oil-formulated diets. Here, we compared nutritionally maximized cells of deceleration growth phase T. lutea and fish oils-formulated product (n-3 HUFA-enriched Chlorella) as a rotifer enrichment diet for enhancement in Japanese flounder Paralichthys olivaceus larviculture. T. lutea had higher concentrations of DHA in the polar lipids than those for enriched Chlorella. Such higher concentrations of T. lutea were estimated only in the deceleration growth phase (not in the logarithmic growth or stationary phase). When deceleration growth phase T. lutea were fed to Brachionus plicatilis rotifers previously cultured on unenriched Chlorella, the DHA of the rotifers was boosted up to the level in those fed with enriched Chlorella. Furthermore, use of T. lutea-fed rotifers for initial feeding of fish larvae enhanced the growth, survival, n-3 HUFA levels, and final juvenile productivity of the larvae as much as feeding the larvae with enriched Chlorella-fed rotifers. We propose that T. lutea in the deceleration growth phase are efficacious, fish oil-free sources of n-3 HUFA for marine fish larviculture. Highlights: Polar lipid DHA % was high in the deceleration growth phase of Tisochrysis lutea. DHA % was high in rotifers fed either T. lutea or fish oil-enriched Chlorella. Rotifers enriched with T. lutea improved marine fish larviculture performance. [ABSTRACT FROM AUTHOR]

Despite significant advancements in ichthyoplankton collection and data processing, challenges persist in the taxonomic identification of these organisms, particularly their eggs. To overcome these challenges, a novel technique has been developed to facilitate the identification of live eggs collected directly in wild. This user-friendly technique includes the collection, processing of the material, and field incubation. Sampling must be conducted using a pelagic net towed at low speed, preferably during early evening. The material processing involves pre-sorting and sorting to remove eggs and larvae. The separated eggs, kept in an aerated bowl, can be identified based on their morphological and meristic characteristics. Unidentified eggs can be placed in plastic bags with oxygen and incubated directly in the aquatic environment for 48–72 h. After this incubation period, the hatched larvae at the yolk-sac or preflexion stage, are identified to the lowest possible taxonomic level. Depending on the study's purpose, hatched larvae and field-collected larvae can be transported to research centers for further development, released back into the natural environment, or fixed to complete the collection. The application of this technique supports management and monitoring programs by identifying spawning areas through egg identification, forming broodstock, and replenishing threatened species, thereby enhancing scientific collections of ichthyoplankton. Additionally, it reduces mortality in ichthyoplankton techniques, including endangered species. Therefore, we believe that this novel taxonomic technique for identifying live ichthyoplankton represents a paradigm shift in the monitoring, management, and conservation of fish, as well as in ecological stewardship and advances in this area of research. [ABSTRACT FROM AUTHOR]

Toxicity mechanisms of per- and polyfluoroalkyl substances (PFASs), a chemical class present in diverse ecosystems, as well as many of their precursors, have been increasingly characterized in aquatic species. Perfluorooctanesulfonamide (PFOSA, C8H2F17NO2S) is a common precursor of perfluorooctane sulfonic acid (PFOS), a long-chain PFAS. Here, we assessed sub-lethal endpoints related to development, oxidative stress, transcript levels, and distance moved in zebrafish embryos and larvae following continuous exposure to PFOSA beginning at 6 h post-fertilization (hpf). PFOSA decreased survival in fish treated with 1 µg/L PFOSA; however, the effect was modest relative to the controls (difference of 10%). Exposure up to 10 µg/L PFOSA did not affect hatch rate, nor did it induce ROS in 7-day-old larvae fish. The activity of larval fish treated with 100 µg/L PFOSA was reduced relative to the solvent control. Transcripts related to oxidative stress response and apoptosis were measured and BCL2-associated X, apoptosis regulator (bax), cytochrome c, somatic (cycs), catalase (cat), superoxide dismutase 2 (sod2) were induced with high concentrations of PFOSA. Genes related to neurotoxicity were also measured and transcript levels of acetylcholinesterase (ache), elav-like RNA binding protein 3 (elavl3), growth-associated protein 43 (gap43), synapsin II (syn2a), and tubulin 3 (tubb3) were all increased in larval fish with higher PFOSA exposure. These data improve our understanding of the potential sub-lethal toxicity of PFOSA in fish species. [ABSTRACT FROM AUTHOR]

Longitudinal dispersal of migratory fish species can be interrupted by factors that fragment rivers, such as dams and reservoirs with incompatible habitats, and indirect alterations to variables, such as water temperature or turbidity. The endangered pallid sturgeon (Scaphirhynchus albus) population in the Upper Missouri River Basin in North Dakota and Montana is an example of such fragmentation and alteration due to the construction of dams. We applied a high-resolution, 2+-dimensional modelling framework composed of hydrodynamic and Lagrangian particle tracking components to simulate pallid sturgeon larval drift and dispersal along a 33-km section of the Upper Missouri River to evaluate three main issues: a comparison between multidimensional models and traditional 1-dimensional models, the sensitivity of hydrodynamics to channel morphology, and the implications of channel morphology on retention and transport-time metrics for larval fish. The results indicate that multidimensional models better represent breakthrough curves of transporting larvae compared to 1-dimensional models, especially for the long tail of slow drifters in the population. Results also indicate that channel morphology and hydraulic complexity play significant roles in larval dispersal with certain flow conditions and channel features increasing larval retention and providing potential management options to increase survival rates by adjusting flow conditions during spawning events. For example, modelling indicates increased retention times at discharges 23–38% daily flow exceedance, coincident with emergence of mid-channel sandbars. Findings additionally emphasize the need for improved understanding of biological factors that affect larval drift and dispersal. [ABSTRACT FROM AUTHOR]

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Simple Summary: This study investigated the use of hormones and temperature control to improve breeding success. Injecting Ovaprim significantly increased egg and sperm production. However, temperature played a critical role. A medium temperature (around 22 °C) produced the best results, with more eggs, faster egg release, and healthier sperm. Both low and high temperatures negatively impacted sperm quality and larval fish survival. Using extender E4 (15% DMSO) for cryopreservation improved fertilization rates. Overall, the study highlights the importance of precise hormone control and temperature management for successful goldfish reproduction, benefiting for fish farming. This study investigates the efficacy of hormone-induced artificial reproduction in goldfish (Carassius auratus) under controlled temperatures. Ovaprim injections significantly enhanced ovulation and sperm production compared to controls. Medium temperature (22 °C) produced the highest ovulation rates, fastest ovulation timing, and optimal sperm quality (motility and morphology) compared to high (28 °C) and low (16 °C) temperature groups. The low-temperature group exhibited reduced sperm motility duration and higher rates of sperm and larvae damage. The sperm volume of the high-temperature group was higher, but their post-injection survival rates were lower. Furthermore, the lowest spawning rate and low egg quality were noted in the high temperature. Cryopreservation using extender E4 (15% DMSO) exhibited superior post-thaw sperm motility and achieved higher fertilization rates. Fertilization rates, embryo development, and larval survival were all highest at the medium temperature. Larvae hatched from fresh sperm at medium temperature exhibited faster growth and fewer deformities. These findings suggest that hormone stimulation coupled with a medium temperature regimen is critical for successful artificial reproduction in goldfish. Cryopreservation with extender E4 holds promise for sperm banking; however, further optimization is necessary to improve fertilization success with thawed sperm. Future research could explore the influence of temperature on sperm physiology and refine cryopreservation protocols to enhance fertilization rates. [ABSTRACT FROM AUTHOR]

This study was conducted using monthly data collected between July 2015 and June 2016 in the marine area of Hamsilos Nature Park, located in Sinop, Southern Black Sea. The primary objectives were to determine the diversity of ichthyoplankton assemblages, examine seasonal variations, assess spatial differences between the inner and outer parts of Hamsilos Bay, and highlight the ecological relationships of the predominant species with environmental factors. The comprehensive collection during the study resulted in a mean abundance of 2217 eggs.10 m2 and 2743 larvae.10 m2, with 28 species belonging to 21 families identified. Specifically, Engraulis encrasicolus is the most abundant in spring and summer, Gaidropsarus mediterraneus is the most abundant in autumn, and Sprattus sprattus is the most abundant in winter. A temporal analysis revealed the highest abundances in August, September, and July, with the lowest in April, May, and February. Significant seasonal differences in abundance and diversity were detected. No spatial differences were found between the inner and outer areas of Hamsilos Bay. Small pelagic species dominated the ichthyoplankton community, while demersal species, though diverse, were less abundant. According to the results of the DistLM analysis, the structure of the ichthyoplankton community is influenced by temperature and salinity. During the study, the water temperature ranged from 8.35 °C in February to 25.50 °C in August, and the salinity varied from 17.67 psu in September to 19.04 psu in May. [ABSTRACT FROM AUTHOR]

Rampant industrialization has led to widespread reliance on hydrocarbon polymers for various commercial applications. While these synthetic polymers, commonly known as plastics, degrade in slowly in the environments, the toxic effects of their micro-sized particles remain underexplored. In this study, we synthesized polyisobutylene (PIB) microparticles in the lab and evaluated their toxicity and accumulation in a zebrafish model. Pristine and fluorescent PIB-microplastics (MPs), with particle sizes ranging from 2 to 10 μm, were synthesized using the solvent evaporation method. Fourier-transform infrared spectroscopy (FTIR) confirmed the stability of the suspensions. Zebrafish larvae exposed to various concentrations of PIB-MPs exhibited numerous morphological and molecular changes, including delayed hatching, impaired swimming behavior, increased reactive oxygen species levels, altered mRNA levels of genes encoding antioxidant proteins, and reduced survival rates. Dissections revealed PIB-MP accumulation in the guts of larvae and adult fish within 7–21 days, causing damage to the intestinal mucosa. These findings provide insights into how contaminants like PIB can induce pathophysiological defects in aquatic fauna and pose potential health hazards to humans. [ABSTRACT FROM AUTHOR]

Larvae nutrition is considered to be the 'bottle neck' for marine finfish culture. Nowadays, marine larviculture can be significantly enhanced by producing new protocols of live feed using modern microbial trends. Primary goals of successful farmed larvae mainly rely on excellent survival and growth, since marine fish larvae record unpredicted high mortality rate and poor performance on designed diets during weaning stage. Adding live or inactive food to the rearing systems is also a widespread technique that has a significant impact on larval survival and performance. The bulk of mass-cultured marine fish larvae still need live feeding species, particularly at the beginning of larval nutrition such as: Artemia (brine shrimp), rotifers Brachionus spp., and microalgae. Bacteria are also added with live food and microalgae in the larval tanks for the rearing water system. Therefore, this review shed light on the developments of water rearing systems and improvements in marine fish larvae diets by discussing different types of live feeds and formulation of weaning microdiets. Since larval development is the most crucial stage of marine aquaculture production during which the greatest death rates can exceed 70%. Hence, the ontogenic development and digestive physiology of fish model larvae are also highlighted. Beneficial effects of prebiotics and probiotics on improving feed utilization and water quality, promoting larval growth and enhancing disease resistance were also discussed. Moreover, additional case studies about live food enrichment and reared fish larvae were presented to elucidate their effective role in improving water quality and larval growth performance. Despite recent substantial advancements in marine larviculture, many questions about fish larvae nutrition remain unanswered and numerous research avenues remain unexplored. Suggestions, recommendations and future considerations were mentioned to improve diets during larval rearing and pinpoint the research gaps that need to be addressed in manual hatchery operations. [ABSTRACT FROM AUTHOR]

The article "WESTERN BOUNDARY CURRENT-SUBTROPICAL CONTINENTAL SHELF INTERACTIONS" discusses the interactions between western boundary currents and subtropical continental shelves, focusing on the transport of heat, nutrients, and biota. The workshop held in Savannah, Georgia in May 2023 brought together researchers to discuss observational strategies, modeling systems, cross-shelf exchange, ecosystem properties, and future climate-related impacts. The article emphasizes the need for interdisciplinary collaboration, improved observational strategies, and accurate modeling to understand and predict the consequences of environmental change in WBC-STCS systems. [Extracted from the article]

Nannochloropsissp is used as natural feed since it contains high good nutrition for the growth of fish larvae. However, the availability of Nannochloropsis sp. is still limited and has become a constraint in aquaculture. This study aimed to address the effect of pasta on the density of Nannochloropsis sp. cultured on the laboratory scale from pasta product of massive culture using the combination of agricultural fertilizer and water extract of Moringaoleifera leaf. Nannochloropsis sp. culture of the laboratory scale used the kw21 fertilizer. The Nannochloropsis sp. seeds were taken from Nannocloropsis sp. pasta with different concentrations, while the control Nannocloropsissp seeds used the laboratory scale without pasta. The study applied a complete randomized design with 4 treatments (NaOH pasta of 75 ppm, 100 ppm, 125 ppm, and control) and 3 replications. The control treatment (D) used the Nannochloropsis sp. of the laboratory scale without pasta. Data analysis utilized the one way-ANOVA, followed by the least significant difference test upon detecting a significant difference. Results indicated the significant effect of the NaOH pasta on Nannochloropsis sp. density. [ABSTRACT FROM AUTHOR]

This study determined the particle release area based on the abundance data of largehead hairtail eggs obtained from the ichthyoplankton surveys in the coastal waters of the southern Yellow Sea (119°E-124°E, 33°N-37°N) conducted from 2018 to 2022. Subsequently, the Finite-volume Coastal Ocean Model (FVCOM) coupled with the Lagrangian particle tracking algorithm was employed to simulate the transport process of largehead hairtail larvae. The primary objectives were to investigate the spawning periods, spawning grounds, and nursery habitats of largehead hairtail in the southern Yellow Sea, and to assess the influence of oceanic conditions on the egg distribution and larval dispersion. The results indicated that largehead hairtail spawned in spring and summer in the southern Yellow Sea with the eggs appeared in May, July and August, and August was the peak spawning month. Largehead hairtail eggs were mainly distributed in 19-30 m waters in May, and 11-70 m waters in August. The sea surface temperature and sea bottom temperature for the presence of largehead hairtail eggs was 13.9-29.7 and 8.4-28.3 ℃ respectively. The Random Forest model analysis revealed that water temperature and depth were the main environmental factors affecting the abundance of largehead hairtail eggs. Particle tracking simulation experiments showed that the particles released in May mainly spread towards the northwest coastal area of the particle release area after 1-15 days (when the swim bladder has not formed and the larvae have no vertical migration behavior), and after 16-40 days (when the swim bladder has formed and the larvae have vertical migration behavior), the particles left the coastal area and spread eastward to the waters near a 50 m water depth. In July and August, before the occurrence of vertical migration behavior, larvae stayed in the near-bottom layer and most of them were transported from the release area to the nearshore waters; After that, larvae moved slightly from the near-shore aggregation area to the off-shore direction. Some of the individuals released in the offshore deep-water areas spread to the north and northeast in a short-distance, and the dispersal pattern did not change significantly in their whole larval stages. Aggregation areas of largehead hairtail larvae derived from field surveys in August were consistent with the results of particle transport simulation experiments. We thought that the season and spatial location of spawning, the diel vertical migration characteristics of larval fish, and the regional upwelling and frontal structure were the dominant factors that shape the transport pattern of largehead hairtail larvae. The results of the study provide a scientific basis for understanding the habitat selection mechanism of egg and larvae stages and early replenishment dynamics of this fish in the southern Yellow Sea, and help for the management and protection of largehead hairtail resources. [ABSTRACT FROM AUTHOR]

Simple Summary: Due to the underdeveloped digestive tracts of larval fish, predigested fish protein has been included in feeds to help increase dietary protein utilization. The predigested protein has been produced from various protein sources and broken down using different methods. This has ultimately led to variable results when included in larval diets, and there is still a lack of an optimal dry diet for larval fish. This study tested the use of adult Walleye muscle as a protein source to provide the optimal dietary amino acid composition for same-species larvae. The muscle was also broken down with enzymes from the adult Walleye gut to predigest protein in a way that mimics the digestion of live Walleye. This protein source was tested against protein produced from muscle and/or enzymes from Nile Tilapia, as a non-species-specific source. The dietary inclusion of predigested protein produced from same-species muscle and digestive enzymes led to increased growth and amino acid absorption in larval Walleye. However, reduced survival in fish fed with the predigested protein suggests that further research is required to improve the pellet stability of the larval diets and reduce the loss of nutrients to the water. Fish protein hydrolysates used in larval diets have been prepared from a variety of fish species, with different enzymes used to hydrolyze the protein. This study's objectives were to determine the effect of the dietary inclusion of fish muscle hydrolysates obtained from species-specific muscle/enzymes—versus hydrolysates produced from muscle/enzymes of a different species—on the growth performance, survival, skeletal development, intestinal peptide uptake, and muscle-free amino acid (FAA) composition of larval Walleye (Sander vitreus). Eight protein products were obtained for this study, comprising an unhydrolyzed and hydrolyzed product from each combination of muscle/enzymes from Walleye and Nile tilapia (Oreochromis niloticus). Four diets were produced, and the dietary protein was provided in a 50/50 ratio of unhydrolyzed and hydrolyzed protein from the respective muscle/enzyme combination. Four groups were fed one of the corresponding formulated diets, and two groups of larvae, fed a commercial starter diet and Artemia, respectively, served as reference groups. Larval Walleye fed the diet containing protein produced with the species-specific muscle and enzymes had a significantly higher weight after the study—30% higher than any other group. A significant interaction effect between muscle and enzyme sources on the growth of Walleye larvae was observed. The species-specific combination also led to a significant increase in postprandial FAA and indispensable amino acid concentrations in muscle. No significant differences were observed between the hydrolysate-fed groups in survival, deformity occurrence, or peptide uptake. Each hydrolysate-based diet significantly reduced skeletal deformities and survival compared to the commercial diet. The results of this study suggest that species-specific muscles and enzymes produce a more optimal dietary protein source for larval fish than non-species-specific products. Further research should focus on improving the physical properties of the formulated diets to reduce possible leaching of hydrolyzed protein and improve the survival of fish larvae. [ABSTRACT FROM AUTHOR]

Ichthyoplankton monitoring is crucial for stock assessments, offering insights into spawning grounds, stock size, seasons, recruitment, and changes in regional ichthyofauna. This study evaluates the efficiency of multi-marker DNA metabarcoding using mitochondrial cytochrome c oxidase subunit I (COI), 12S rRNA and 16S rRNA gene markers, in comparison to morphology-based methods for fish species identification in ichthyoplankton samples. Two transects with four coastal distance categories were sampled along the southern coast of Portugal, being each sample divided for molecular and morphological analyses. A total of 76 fish species were identified by both approaches, with DNA metabarcoding overperforming morphology—75 versus 11 species-level identifications. Linking species-level DNA identifications with higher taxonomic morphological identifications resolved several uncertainties associated with traditional methods. Multi-marker DNA metabarcoding improved fish species detection by 20–36% compared to using a single marker/amplicon, and identified 38 species in common, reinforcing the validity of our results. PERMANOVA analysis revealed significant differences in species communities based on the primer set employed, transect location, and distance from the coast. Our findings underscore the potential of DNA metabarcoding to assess ichthyoplankton diversity and suggest that its integration into routine surveys could enhance the accuracy and comprehensiveness of fish stock assessments. [ABSTRACT FROM AUTHOR]

Diets of fish larvae may vary within populations and among species and are affected by larval prey availability and foraging capacity. We aimed to describe the diet of fish larvae based on empirical field observations, emphasizing the interaction and organization of the predator–prey network using Auchenipterus osteomystax as a species model. The network showed few interactions (low connectance and modularity) but a nested structure (some items that had fewer records tended to occur together with the most frequent ones), low complementary specialization (the proportions of ingested items tended to be equivalent) and a pattern of segregation (some items tended not to be consumed together) in the use of resources among individuals. Robustness was low when the removal of prey with a higher consumption frequency occurred. The correlation between morphological variables and network attributes was significant and positive for abundance and strength, while the correlation with nested rank was negative. The availability of suitable dietary resources is likely to be the key factor for success and survival in the early stages of development. With changes in morphology during larval development, A. osteomystax showed a generalist position in the network as its predation capacity increased. A new approach to trophic ecology studies of fish larvae incorporating network analysis may help explain the individual characteristics of larvae and assess the pattern of interactions in the population. [ABSTRACT FROM AUTHOR]

Computing Lagrangian trajectories with ocean circulation models is a powerful way to infer larval dispersal pathways and connectivity. Defining release areas and timing of particles to represent larval habitat realistically is critical to obtaining representative dispersal pathways. However, it is challenging due to spatial and temporal variability in larval density. Forward-tracking particle experiments were conducted to study larval connectivity of four species (neritic or mesopelagic) in the Gulf of Mexico's (GoM) deep-water region. A seasonal climatology coupled with predicted potential larval habitat models based on generalized additive models was used to delimit the particle dispersal origin. Two contrasting mesoscale circulation patterns were examined: (1) high Loop Current (LC) intrusion, absence of recently detached LC anticyclonic eddies (LC-ACE), and no interaction between LC-ACEs and the semi-permanent cyclonic eddy (CE) in the Bay of Campeche (BoC), and (2) limited LC intrusion, a recently detached LC-ACE, and interaction between LC-ACEs and the BoC's CE. To simulate larval transport, virtual larvae were randomly released in the potential habitats and advected for 30 days with the velocity fields of the HYbrid Coordinate Ocean Model with hourly-resolution assimilation. Potential habitat location and size played a major role in dispersal and connectivity. A greater percentage of particles were retained in potential habitats restricted to the southern BoC, suggesting lower connectivity with other GoM regions than those encompassing most of the BoC or the central Gulf. Mesoscale feature interactions in the western GoM and BoC led to greater dispersion along the western basin. By contrast, the absence of ACE-CE interaction in the BoC led to greater retention and less connectivity between the southern and northern GoM. Under high LC intrusion, particles seeded north of the Yucatan Shelf were advected through the Florida Straits and dispersed within the GoM. Coupling potential habitat models with particle experiments can help characterize the dispersal and connectivity of fish larvae in oceanic systems. [ABSTRACT FROM AUTHOR]

One of the most persistent challenges in walleye larviculture is the high rate of unobserved mortality occurring within the first 30 days post-hatch. Walleye larviculture is characterized by high mortality rates, but oftentimes, only a fraction of the total mortality in walleye larviculture is observed. Unobserved mortality is frequently attributed to a high rate of cannibalism, but decomposition of larvae and other factors may also be important contributors. Unobserved mortality can make walleye larviculture especially challenging as accurately estimating daily feed rations and forecasting larval production rely on accurate counts of surviving fish. Despite the importance of unobserved mortality, there is little empirical evidence available that assesses the temporal occurrence and causes of unobserved mortality in walleye larviculture. This study assessed when unobserved mortality occurs during walleye larviculture by examining survival at three timepoints (8, 15, and 30 days post-stocking). Tanks were cleaned daily and dead fry were enumerated to account for observed mortality. At the end of each treatment period, the tanks were drained, all remaining fry were enumerated, and the unobserved mortality rate was calculated. While observed mortality trended higher as trial duration increased, unobserved mortality did not increase significantly from the 8-day treatment suggesting that the bulk of unobserved mortality occurs during the first 8 days of walleye larviculture. [ABSTRACT FROM AUTHOR]

High larval and frymortality has been amajor challenge to the commercial culture of the African bony-tongue (Heterotis niloticus). Research indicates inadequate feeding to be a possible cause of the high mortality rates of larvae/fry grown in captivity. An experiment was conducted to first describe the developmental stages of H. niloticus eggs and larvae until schooling, 6 days after hatching (DAH), at 26°C. The morphological development, survival, growth (weight gain and length), and swimming behavior of the larvae were monitored. A follow-up feeding trial was conducted with H. niloticus fry from 6 to 27 DAH involving four treatments: feeding with Artemia nauplii; a combined feed of 50% Artemia nauplii and 50% rotifers (w/w); feeding with rotifers; and no feeding. The activities of three digestive enzymes (trypsin, lipase, and amylase)were assessed in fry exposed to the live feed treatments. At hatching, the larvae had a large, vascularized yolk sac filled with yolk platelets, which occupied approximately one-third of the total body length of the abdominal cavity. Yolk platelet reabsorption started at 1 DAH and was complete at 6 DAH. Metamorphosis was completed at 6 DAH, and schooling behavior was observed. For the feeding trial, the fry that received Artemia nauplii underwent the fastest development until 27 DAH. Similarly, the survival rate was considerably higher in fry fed with Artemia nauplii than in those that received a combination of Artemia nauplii and rotifers or only rotifers. Overall, the survival rates for fry fed with Artemia nauplii and larvae co-fed were 72.7% ± 0.9% and 41.2% ± 3.3%, respectively. Fry did not survive until 27 DAH in the rotifer-fed and unfed treatment groups. Digestive enzyme activity differed significantly (p< 0.05) between treatments and sampling dates. All digestive enzymes were detectable at the onset of mouth opening (5 DAH) and fluctuated through the 7 and 9 DAH. Lower enzyme activity was observed when the fry were subjected to starvation or the rotifer treatment. Results indicate that Artemia nauplii is the best live feed organism for H. niloticus larviculture. [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]