Fishes, Volume 10, Issue 2 (February 2025) – 26 articles

Post-smolt Atlantic salmon were fed control (C), plant protein- (PP), and animal protein (AP)-based diets over a 90-day period. At trial start, the outline shape variation in the salmon body was recorded using two-dimensional Cartesian coordinates of a combination of 12 landmarks (LM) and three semi-landmarks from each of the 48 fish. The identical landmarks were then assessed at trial end for the differing dietary treatments. These datasets were used to determine whether diet exerted a measurable effect on body shape to enable authentication of fishmeal/fish oil-free status. Most differences in shape at trial end were visualized at the base of the dorsal and pelvic fins and caudal peduncle. The greatest shape variation between PP and AP groups was found at the base of the pectoral and pelvic fins. While PP and AP groups were more similar in shape than control fish, the recorded differences were not significant enough to verify dietary origins. The number of animals employed and the length of the trial period were likely insufficient to distinguish alterations in body shape with any certainty. Future trials should employ larger numbers of animals and be of longer length to verify whether PP-based feeds cause changes in body shape. Full article

Myxozoans represent a significant group of parasitic pathogens affecting both wild and farmed fish. For accurate and comprehensive early detection, the composition of myxozoan pathogens in fish has consistently been a primary focus for parasitologists. In China, we undertook an investigation into myxozoan infection in fish from Shandong Province, China, successfully isolating a myxozoan species from gibel carp Carassius auratus gibelio Bloch, 1782 and goldfish C. auratus Linnaeus, 1758. In the present study, this myxozoan species was identified by detailed morphological and molecular analysis. This parasite is characterized by the presence of visible plasmodia in various organs (intestine, liver, gallbladder, and abdominal cavity) of gibel carp as well as the abdominal cavities of goldfish. In comparison to all documented myxozoan species, this myxozoan species exhibits morphological identity with Myxobolus pronini Liu, Batueva, Zhao, Zhang, Zhang, Li, Li, 2016, in terms of spore morphology. Molecular sequence analysis, including sequence similarity, variable site, and the secondary structure of SSU rRNA, indicates that the present myxozoan species closely resembles M. pronini. Furthermore, phylogenetic analyses revealed that all isolates collected from different organs and hosts in this study clustered with M. pronini, forming a distinct branch within the Carassius-infecting clade. Consequently, the present myxozoan species can be confidently identified as M. pronini. Compared with the previous reports on M. pronini, this study documents, for the first time, goldfish as a host, intestines and gallbladders as the sites of infection, and Shandong Province as the geographic distribution of this myxozoan species. Full article

An 8-week rearing trial was designed to estimate the dietary protein requirement and evaluate the effects of dietary protein on growth performance, plasma parameters, and digestive enzyme activities of blunt snout bream at two growth stages. Six practical diets were prepared to feed two sizes of fish (larger fish: initial weight of 153.69 ± 0.85 g; smaller fish: initial weight of 40.89 ± 0.28 g) with graded protein levels (26%, 28%, 30%, 32%, 34%, and 36%). Our results show that the final weight, weight gain (WG), and specific growth rate (SGR) of the fish initially rose to peak values and then declined as the dietary protein levels increased. The higher WG and SGR were recorded in the larger fish fed diets containing 30%, 32%, and 34% protein, and in the smaller fish fed a 30% protein diet, all significantly higher than those in the control group (p < 0.05). No significant differences were observed in the feed conversion ratio (FCR), viscerosomatic ratio (VR), hepatosomatic index (HSI), condition factor (CF), or survival rate among the treatments at both growth stages (p > 0.05). The plasma total protein (TP) content was highest at both growth stages in fish fed a 30% protein diet (p < 0.05). As the dietary protein level increased, the plasma urea content of the larger fish increased, peaked in the 34% protein group (p < 0.05), and then remained stable. In contrast, no significant difference in the plasma urea content was seen among the treatment groups of the smaller fish (p > 0.05). Protease activity in the fish foregut at both growth stages peaked in the 32% protein group (p < 0.05). In the midgut of the larger fish, protease activity was higher in the control group, while in the smaller fish, it was higher in the 36% protein group (p < 0.05). In the larger fish, hindgut protease activity was higher in the 34% protein group (p < 0.05), while in the smaller fish, there was no significant difference in the hindgut protease activity among all groups (p > 0.05). The dietary protein levels had no significant effect on lipase activity in the foregut, midgut, or hindgut, or on amylase activity in the foregut or midgut of the fish at the two growth stages (p > 0.05). However, hindgut amylase activity was highest in the control group of the smaller fish (p < 0.05). Based on regression analysis, the optimal dietary protein levels for the larger and smaller fish were 30.45% and 29.95%, respectively. Overall, appropriate dietary protein levels (30%) could improve the growth performance, immune function, and health status of fish at two growth stages and promote the adaptive response of their digestive system, especially the spatial regulation of protease activity in different gastrointestinal regions. Full article

Changes in the environment promote variations in fish physiological responses. Genetic variation also plays a role in physiological variation. To explore the role of genetics in physiological variation, we assessed variation of cardiac function (heart rate, stroke volume, and cardiac output), oxygen consumption, yolk conversion efficiency, and cost of development in embryonic and larval AB wild-type and NHGRI-1 zebrafish (low heterozygosity line backcrossed from AB wild-type) exposed to different temperature and oxygen regimes. Fish were exposed from fertilization to 7 days post-fertilization (dpf) to control conditions (28 °C, 21% O₂) or to low temperature (23 °C, 21% O₂), high temperature (33 °C, 21% O₂), moderate hypoxia (28 °C, 13% O₂), or severe hypoxia (28 °C, 10% O₂). We hypothesized that (1) assessed physiological variables will respond similarly in both fish lines and (2) data variability in the low heterozygosity NHGRI-1 zebrafish will be lower than in AB zebrafish. Cardiac function decreased at lower temperature and in hypoxia in both AB and NHGRI-1 zebrafish. Oxygen consumption was increased by higher temperature and hypoxia in AB fish and by severe hypoxia in NHGRI-1 fish. Yolk conversion efficiency was decreased by lower temperature and hypoxia in AB fish and increased by higher temperature and decreased by hypoxia in NHGRI-1 fish. Cost of development was higher mainly in hypoxia-treated fish. Supporting our hypothesis that genetics contributes to physiological variation, NHGRI-1 zebrafish data showed significantly lower coefficients of variation in 84% of assessed endpoints. We conclude that (1) there is a strong genetic component to physiological variation in fishes and (2) low heterozygosity NHGRI-1 zebrafish are useful models for reducing the ‘noise’ from genetic backgrounds in physiological research in fish, which may aid interpretation of experimental results and facilitate reproducibility. Full article

Trematomus bernacchii is a widely distributed, commercially valuable species that plays a significant role in the Benthic ecosystem of the Southern Ocean. Current research mainly explores its molecular responses to cold adaptation and environmental stress, while questions regarding its biological characteristics, such as length-related and sex-related differences in diet, remain to be addressed. This study assessed the age and feeding habits of T. bernacchii in the Ross Sea through stomach content morphological analysis and DNA metabarcoding analysis, examining dietary shifts by growth and sex. The research revealed that T. bernacchii primarily feeds on fish eggs, polychaetes, echinoderms, and mollusks. Other dietary components include algae, cnidarians, and crustaceans. Minor dietary differences were found between sexes. Polychaetes dominated all size classes, with Crustacea and Cnidaria declining as body length increased, while Echinoderms and Mollusca were more abundant in larger specimens. Evidence of egg cannibalism was also noted. These findings enhance our understanding of the trophic ecology of T. bernacchii and contribute to the construction of the Benthic food web of the Ross Sea. Full article

Rapid and coordinated test growth is crucial for maintaining the normal body shape of Strongylocentrotus intermedius juveniles. In total, 270 S. intermedius (1.19 ± 0.01 g) were randomly assigned to 18 floating cages. Three cages of sea urchins were fed kelp (Saccharina japonica) (control diet) or one of five formulated feeds with different carbohydrate-to-lipid ratios (C/L) (1, 2, 4, 8, and 16) for 90 days. The results suggested that the weight gain rate of S. intermedius fed C/L4 was markedly greater than that fed C/L1 and C/L16 except for kelp, C/L2, and C/L8. The test diameter (TD) and test height (TH) gain rates of S. intermedius fed C/L4 were markedly greater than those fed other dry feeds except for C/L2. The TH/TD of S. intermedius fed kelp was markedly greater than that fed dry feeds, except for C/L1 and C/L2. Juvenile S. intermedius fed C/L2 showed higher test magnesium content, larger holes, and longer and thinner trabeculae than those fed other dry feeds. Overall, juvenile S. intermedius fed C/L4 had the highest body weight gain rate and test growth rate among the formulated feed groups. Juveniles fed C/L2 had the most coordinated test growth reflected by TD/TH, which is comparable to those fed kelp. Therefore, the optimal C/L for rapid and coordinated test growth of juvenile S. intermedius should be higher than 2 but lower than 4. Full article

The lower reaches of the Yarlung Zangbo River are one of the most important biodiversity hotspots worldwide. With the rapid economic development in the area coupled with global climate change, the fish resources and diversity of this region are experiencing serious threats. Basic biological information on most fishes in the river is limited, restricting the conservation of local fish resources. This study aimed to provide estimates of length–weight relationships (LWRs) for six fish species from the lower Yarlung Zangbo River catchment, Tibet, China. From 2023 to 2024, 4034 specimens belonging to two families, five genera, and six species were collected using various types of fishing techniques. The LWRs of five species, namely Schizothorax curvilabiatus, Schizothorax molesworthi, Pseudecheneis sulcata, Parachiloglanis hodgarti, and Exostoma labiatum were reported for the first time to FishBase, except Garra tibetana. The b values calculated from the LWRs ranged between 2.738 and 3.172, and the r² values for all LWRs estimates ranged from 0.931 to 0.989. Sexual variations of LWRs were observed in S. molesworthi and P. sulcata; seasonal variations were detected in S. curvilabiatus, S. molesworthi, G. tibetana, P. sulcata, and P. hodgarti; and geographical differences were discovered in S. molesworthi, G. tibetana, P. sulcate, P. hodgarti, and E. labiatum. Additionally, this study updated information for FishBase by providing a new record of maximum standard length for S. curvilabiatus, S. molesworthi, G. tibetana, and P. hodgarti and a new record of total length for P. sulcata. The findings of this study are essential for the management and conservation of locally indigenous fish and fisheries. Full article

Using fishes as indicators of estuarine degradation is informative in long-term monitoring programs. Beach seine hauls were used in four estuaries that differed in their trophic and tidal status. The study found that inner, middle, and outer estuarine nearshore fish communities differed significantly at from all estuaries, for all sampling times. To reduce the effects of within-estuary variability, between-estuary differences were examined separately for inner, middle, and outer estuarine areas. These analyses revealed differences in north-south and trophic status in communities between estuaries. The north-south differences were characterized by more benthic fishes, such as mummichogs and fourspine stickleback in the microtidal northern estuaries and proportionally more pelagic fishes, such as Atlantic silversides and river herring in the mesotidal estuaries. In both multivariate and univariate analyses, mummichogs were also featured as being most abundant in the more eutrophic estuaries. The distance-based redundancy analysis showed that bare sediment coverage was the strongest correlate of the north-south differences, while the Ulva to Zostera plant gradient was more influential in predicting eutrophication impacts on communities in the inner and middle estuary. Full article

The concept of Quality of Aquaculture Services (QoAS) is inspired by the Quality of Service (QoS) principle, originally developed in the field of networks and telecommunications, where it refers to the ability to guarantee the quality, availability, and priority of service in a communications system. Adapted to the aquaculture context, QoAS is fundamental to maximising the benefits of Integrated Multi-Trophic Aquaculture (IMTA). IMTA has emerged as a sustainable approach to meet the growing global demand for aquatic food products by combining species from different trophic levels in a single system, optimising resource use, improving environmental performance, and diversifying production. However, ensuring QoAS in these complex systems requires the implementation of advanced technologies to monitor, manage, and optimise every aspect of the aquaculture process. This article presents a comprehensive review of technologies applied at IMTA, focusing on IoT-based monitoring systems, resource management algorithms, water recirculation technologies, intelligent automation, biosecurity, and data management platforms. Our review finds that IoT and automation-based solutions significantly enhance real-time monitoring, increasing operational efficiency and environmental sustainability. Key challenges identified include integration complexity, high costs, and technical expertise requirements, but the ongoing development of modular, user-friendly solutions indicates a promising trajectory. This review highlights the transformative role of technological innovation in IMTA, providing a foundation for future research and advancements in QoAS management in aquaculture. Full article

The Southeastern U.S. Atlantic coast (North Carolina to Florida, U.S.A.) has undergone considerable environmental change in recent decades, including increasing coastal water temperature and human development. The region is also home to a diverse suite of exploited reef fish species, including the southern stock of black sea bass (Centropristis striata). The objective of the current study was to compare trends in black sea bass year class strength and central location captured by trawls (age 0) and traps (age 2) as well as compare those trends to regional bottom temperature. We found no correlation between age 0 and age 2 abundance when comparing the same year class, suggesting that the numbers of trawl-caught juveniles cannot predict the number of adults available to the fishery. Larger year classes observed in traps were correlated with centers of abundance farther south in the region, while smaller year classes corresponded with more northerly centers of abundance. In both trawls and traps, strong year classes occurred following years with below-average regional water temperatures, and a series of recent, weak year classes correspond with recent higher-than-average water temperatures. It is unclear whether correlations between shifting centers of abundance, year class strength, and regional bottom temperature indicate a range contraction for the southern stock of black sea bass or movement into areas previously inhabited by the northern stock of the species. Full article

Peripheral blood has been always used as the mirror of physiological status in a minimally invasive manner. In homeothermic vertebrates, different blood parameters have been correlated to a variety of biochemical and physiological processes and the establishment of physiological values have rendered them valuable indicators for research, diagnosis, and welfare status. Despite the volume of research in fish physiology and teleost significance for food security, information about the physiological values of minimally invasive biomarkers is still fragmented while there is a great need for such biomarkers for monitoring fish health, welfare, and factors that can impact their homeostasis. For the first time, we have focused on determining the physiological ranges of cholesterol, triglycerides, and total proteins in the plasma of gilthead sea bream (Sparus aurata) and detecting how size, diet, environment, and genetic background may influence these levels. A large heterogeneous dataset of 5318 healthy individuals of two different size classes (1–100 g; 101–200 g), dietary status (10 feeds and feeding regimes), and different genetic background (125 families), in combination with different geographic locations (GxE), was produced over a period of three years and analyzed to ensure a comprehensive representation in establishing the physiological range for these biomarkers. Dietary status and GxE introduced significant variations in the range of the physiological values of all biomarkers in both size classes. Triglyceride, total protein and cholesterol values did differentiate with age/size. Interestingly, all parameters responded to diet in a size-specific way, revealing their potential as biomarkers of dietary status. Full article

Broadband backscattering measurements of Pacific mackerel (Scomber japonicus) can improve acoustic surveys of the species for the management of its fisheries throughout the Pacific Ocean. The determination of its target strength (TS), the logarithmic form of the backscattering cross-section, is the aim of this work. It was measured for fourteen individual specimens, eight in a freshwater tank and six in a seawater tank, using calibrated broadband echosounders spanning the frequency band 24–84 kHz. The TS is expressed as a function of frequency and tilt angle, with fish length as a parameter. The individual broadband TS patterns with the tilt angle of fish showed size and frequency dependencies. The fish length-normalized TS of mackerel decreased with increasing fish length-to-acoustic wavelength ratio (l/λ) in the small l/λ range (approximately 2–6) but was flat in the larger l/λ range (>6). This variation in the normalized TS indicates that a pair of regression equations is necessary to span the range of commercially important mackerel relative to the acoustic wavelength. The relative l/λ characteristic of the normalized TS showed constant values with tilt-angle distributions over a large l/λ range and can be used as a characteristic of acoustic backscattering for discrimination among species. Full article

The effects of three types of feed, purchased from online stores and having similar prices, on the growth performance and culture environment of crucian carp (Carassius auratus) were studied in this experiment, which aimed to provide a reference for the evaluation and selection of fish feed. The results showed that feeding different feeds had a significant effect on crucian carp, and that the growth-promoting effect of HD feed (feed produced by Haida Company Limited) was significantly better than that of the other two feeds. For example, the weight gain rate (WGR) of fish in the HD group was 47.1% higher than that in the LD group (p < 0.05), and the WGR of fish in the LD (feed produced by Lianda Company Limited) group was 81.4% higher than that in the TW (feed produced by Tongwei Company Limited) group (p < 0.05). Moreover, the activities of superoxide dismutase and catalase in fish in the HD group was significantly higher than that in the LD and TW groups. Furthermore, we found significant differences in the environmental effects of feeding different feeds. Compared to the LD and HD groups, the environmental impacts for the TW group were more pronounced. The body weight of crucian carp first increased and then stabilized with increasing total dissolved solids (TDS) values. Their quantitative relationship was established based on the von Bertalanffy and Logistic equations (R² = 0.942–0.995). The results above indicate that, due to differences in feed formulation and the quality of feed raw materials, different feeds have a significant impact on the growth performance and antioxidant indices of fish, as well as on the water environment. Therefore, selecting the appropriate feed is crucial for promoting high-quality development in the aquaculture industry. Full article

Replacing traditional agricultural ingredients with biotechnologically improved agro-industry by-products in fish diets promotes sustainable aquaculture, reduces production costs and carbon footprint, and promotes a circular economy. Brewer’s spent grain (BSG) is one such by-product. Solid-state fermentation (SSF) of BSG with Aspergillus ibericus enhances its nutritional value and digestibility for European seabass. The present study further evaluates the potential of dietary inclusion of BSG-SSF on growth performance, feed utilization, plasma metabolite profile, intermediary metabolism, and oxidative status of European seabass juveniles compared to the unfermented product. A practical diet (45% protein; 18% lipids) was tested against diets incorporating 10% or 20% of BSG or BSG-SSF, replacing plant-protein feedstuffs. Triplicate groups of European seabass juveniles (49 g initial weight) were fed for 10 weeks. Unfermented BSG (10% and 20%) reduced growth and feed efficiency. In comparison, the 20% BSG-SSF diet promoted growth and feed efficiency similar to the control group, while the 10% BSG-SSF diet surpassed the control diet. Whole-body protein content was unaffected, but lipid and energy content decreased with increasing BSG levels, regardless of fermentation. Plasma glucose and phospholipid levels and hepatic activities of glucokinase and malic enzymes decreased with increasing BSG, irrespective of fermentation. BSG-SSF incorporation increased plasma triglyceride levels and decreased hepatic transaminase activities but did not affect hepatic key enzyme activity of β-oxidation or lipogenesis. It also reduced antioxidant enzyme activity and lipid peroxidation. In conclusion, BSG negatively impacted growth performance, while BSG-SSF supported inclusion levels up to 20% without performance loss. Further, the 10% BSG -SSF diet outperformed the control diet. Full article

Phosphorus is essential for all life forms on Earth, including eukaryotes (animals, plants, fungi, and protists), prokaryotes (bacteria and archaea), and even viruses. Its significance stems primarily from its presence in nucleic acids (DNA and RNA), where it forms a crucial part of the backbone structure. Beyond this, phosphorus plays a pivotal role in countless biological processes, supporting life at its core. In this article, the author explores the possible causes of stomach loss, focusing specifically on phosphorus absorption, vertebral calcification, and reproduction. Large gonads, characteristic of external fertilization, require substantial amounts of phosphorus for gametogenesis in both females and males, particularly in the latter. This demand has driven the evolutionary calcification of vertebrae, which serve as a phosphorus storage organ. Moreover, to efficiently absorb phosphorus from their diets, shellfish-eating fish have evolved to either lose their stomachs or reduce gastric acidity, minimizing the formation of calcium phosphate precipitates in the intestine. Full article

The aquafeed industry evolved alongside fish farming, utilizing scientific and technological advancements to incorporate a variety of feed additives, supplements, and alternative ingredients in the nutrition and feeding of fish in aquaculture. These advances played a significant role in improving the production, health, and welfare of farmed fish. Recent research in Brazil highlighted the importance of using fish feed additives, such as vitamins, minerals, and amino acids, to ensure that farmed fish receive all the necessary nutrients for growth and health. Functional additives can enhance the immune system, boosting disease resistance and promoting the overall health of fish. Antimicrobial and antiparasitic additives help prevent and treat infections and infestations, reducing the occurrence of disease outbreaks. Additionally, some additives improve feed digestibility, leading to better nutrient absorption and reduced feed requirements. Overall, nutritional strategies are essential for optimizing fish farming practices in Brazil and globally, promoting fish health and sustainability in the industry. This review emphasizes the significance of certain additives, supplements, and ingredients strategically incorporated into experimental feeds for research in Brazilian fish farming. It also underscores the necessity for ongoing research. There is a noticeable trend towards developing more sustainable and efficient feeds, which is essential for the future of sustainable aquaculture. The goal is to minimize environmental impacts while maintaining economic viability in aquaculture operations. Full article

Sea cucumbers are valuable in aquaculture, but their cultivation faces challenges from diseases such as skin ulceration syndrome caused by Vibrio alginolyticus (VA). This study aimed to isolate and identify probiotics capable of combating VA and improving sea cucumber’s growth performance. Pathogenic VA was identified, through 16S rDNA sequencing, confirming its high genetic similarity (>99%) to Vibrio alginolyticus. Two Bacillus strains, Bacillus licheniformis YB-1, and Bacillus megaterium YB-2, were isolated as potential probiotics, with identification supported by 16S rDNA phylogenetic analysis and deposition in microbial culture collections. They demonstrated strong antibacterial activity against VA in vitro without exhibiting antagonism when combined. Probiotic tolerance to environmental stressors was observed, while feeding trials revealed significant growth improvements in sea cucumbers, with the highest specific growth rates observed at 1 × 10⁶ CFU/mL for both strains. Immersion challenge tests showed that sea cucumbers treated with probiotics exhibited reduced symptoms of rotten skin syndrome and higher survival rates. The optimal combination of YB-1 and YB-2, with viable bacteria concentrations of 5 × 10⁷ CFU/mL each, achieved a 55% survival rate after a VA challenge, demonstrating their synergistic efficacy. These findings suggest that YB-1 and YB-2 offer promising probiotic solutions for enhancing sea cucumber health and resistance to VA infections in aquaculture. Full article

The Ylistrum japonicum is a scallop of commercial significance, renowned for its capacity to undertake long-distance swimming. A total of 150 individuals were collected to explore the connections between morphological traits and quality traits and to determine the nutritional components of the adductor muscle. The results showed a robust positive correlation between morphological traits and quality traits, with certain variations in the intensity of the correlation depending on gender. For both female and male individuals, the most significant factor directly influencing the quality traits was shell width, and shell length had the greatest indirect influence on the individual quality traits. The nutritional results of the adductor muscle of Y. japonicum showed that the moisture content was 80.17%, the ash content was 1.43%, the protein content was 16.93%, the fat content was 0.67%, and the carbohydrate content was 0.80%. Furthermore, a total of 17 amino acids and a total of 23 fatty acids were detected. The study’s findings contribute to the understanding of the quality traits and nutritional value of Y. japonicum, laying a basis for the development of selective breeding strategies aimed at boosting the species’ aquaculture potential. Full article

Ecological floating beds are effective in mitigating lake eutrophication. To examine the effects of their in situ remediation processes on the food sources and trophic structures of consumers, particularly fish, this study used stable isotope techniques to compare cage enclosures, net enclosures, and natural lake area in Meiliang Bay, Lake Taihu. The results revealed that among basic carbon sources, only the δ¹³C values of phytoplankton and POM differed significantly, while most consumers showed no significant differences in carbon and nitrogen stable isotope characteristics across the three remediation areas. In cage enclosures, the food chain transitioned from being grazing-based, dominated by phytoplankton, to detritus-based, primarily relying on SOM. In contrast, net enclosures enhanced the utilization of phytoplankton. The trophic levels of most consumers in cage enclosures were significantly lower than those in net enclosures and the natural lake area. Trophic niche indices indicated that cage enclosures exhibited the highest trophic diversity and the lowest trophic redundancy. The in situ remediation using ecological floating beds altered the food resource conditions within the remediation areas due to differences in the degree of enclosure provided by the floating beds and interception facilities. These changes have consequently reshaped the internal trophic structure through trophic cascade effects. Full article

Hydrological changes caused by dam construction are among the primary drivers of global freshwater biodiversity decline. To assess the current status of fish community diversity and examine the impacts of cascade hydropower development on fish diversity, this study employed environmental DNA (eDNA) technology from 2023 to 2024 to conduct seasonal surveys at 18 sampling sites across six river segments separated by five dams in the downstream section of the Fujiang River. The study aimed to uncover the temporal and spatial dynamics of fish diversity and community structure, as well as to analyze the influence of environmental factors on these patterns. The results identified 84 fish species spanning 60 genera, 19 families, and 7 orders, including 2 nationally protected species, 11 endemic species of the upper Yangtze River, and 13 alien species. The cascade dams were found to have significantly reduced fish diversity compared to historical records, with a marked decline in native species and a rise in alien species, contributing to the miniaturization and homogenization of fish communities. Environmental factor analysis revealed that chemical oxygen demand (COD), dissolved oxygen (DO), total dissolved solids (TDSs), electrical conductivity (EC), and reservoir formation time were significant drivers of fish community structure and diversity. This study provides essential baseline data on fish diversity under the influence of cascade hydropower development in the Fujiang River. It also offers valuable insights into the current status of fish resources and supports efforts in fish conservation and aquatic ecosystem management in the region. Full article

As the global demand for aquafeed ingredients continues to rise, sourcing sustainable alternatives is crucial for aquaculture industries. This study aimed to explore the potential of enzymatic hydrolysate as a substitute for traditional fishmeal and soybean meal in diets for juvenile sea cucumbers (Apostichopus japonicus). Three isonitrogenous (15% crude protein) and isolipidic (2.4% crude lipid) diets were formulated: a control diet containing 10% fishmeal and 5% soybean meal and two experimental low-fishmeal (8%) and low-soybean meal (0%) diets, supplemented with either 8% enzymatically hydrolyzed fish stickwater (EFS) or 8% enzymatically hydrolyzed chicken pulp (ECP), designated as Control, EFS, and ECP, respectively. Juvenile sea cucumbers (initial body weight, 0.25 ± 0.01 g) were fed these diets for 84 days to evaluate the effects of ECP and EFS on their growth performance, antioxidant capacity, and inflammatory responses. The results revealed significantly higher final weights and specific growth rates in both experimental groups than the control (p < 0.05). The proximate chemical compositions of sea cucumber were less affected by the diets (p > 0.05). Compared with the control group, significantly elevated levels of digestive enzymes, antioxidants, and lysozyme, together with lower malondialdehyde levels, were recorded in the experimental groups (p < 0.05). ECP appeared to exhibit greater potency than EFS in enhancing growth performance and antioxidant capacity. Similar trends were observed in the mRNA expression of SOD, CAT, and inflammation-related genes across the groups. In a nutshell, both ECP and EFS supplemented in a low-fishmeal and low-soybean meal diet could effectively promote the growth and health of A. japonicus, with ECP showing a superior effect over EFS. These findings suggest that enzymatic hydrolysate demonstrates potential as a viable alternative to traditional fishmeal and soybean meal in diets for sustainable sea cucumber aquaculture. Further investigations are warranted to reveal its underlying mechanism. Full article

To better understand the population genetic structure and molecular biological background of Conger myriaster, an economically important marine fish, a total of 217 complete mitochondrial cytochrome b (Cyt b) gene sequences with a length of 1142 bp were obtained to assess the genetic diversity, population differentiation, and demographic history of seven populations along the coastal waters of China. The analysis of population genetic diversity showed a high level of haplotype diversity and a low level of nucleotide diversity. The analysis of molecular variance (AMOVA) and the genetic differentiation coefficient (F_ST) showed that most of the variation came from within populations, and the geographic distribution of haplotypes revealed non-significant genetic differentiation among populations. Tracing the population dynamic history, the results of the neutrality test and mismatch analysis suggested that the populations of C. myriaster in coastal China seas had experienced demographic expansion, and the expansion time can be traced back to the middle Pleistocene period. These results provide supplemental information for the sustainable utilization of fishery resources of this species. Full article

Onychostoma macrolepis is not only a protected Cyprinid species in the wild but also an emerging commercial aquaculture fish in China. The objective of this research was to genetically modify the genes associated with commercial traits by CRISPR/Cas9 for the protection and utilization of the germplasm resources of O. macrolepis. To that end, one-cell stage embryos were obtained via hormone-induced ovulation and artificial insemination in O. macrolepis. Eight genes related to body color, growth, intermuscular bone, and sex differentiation were mutated in O. macrolepis using the CRISPR/Cas9 system by microinjection of gRNA/Cas9 mRNA. The optimal dose of gRNA/Cas9 mRNA was determined by injection of different concentrations of tyr (tyrosinase)-gRNA/Cas9 and examination of the mutation rate and hatching rate of embryos. Indels were detected by T7 endonuclease I digestion and Sanger sequencing. F0 mutants with high mutation rates were selected for phenotype analyses. Disruption of body color gene tyr, mpv17 (mitochondrial inner membrane protein MPV17), and csf1ra (colony-stimulating factor 1 receptor, a) resulted in obvious phenotype with decreased or even absence of melanophores, iridophores, and xanthophores, respectively. Mutation of mstnb (myostatin b) led to improved growth performance. Mutation of mc4r (melanocortin 4 receptor) led to no obvious phenotype. Mutation of runx2b (RUNX family transcription factor 2b) and bmp6 (bone morphogenetic protein 6) resulted in decreased or absence of intermuscular bones, as revealed by alizarin red S staining. Mutation of cyp19a1a (cytochrome P450, family 19, subfamily A, polypeptide 1a) resulted in ovarian degeneration as revealed by gonadal histological examination. Therefore, this study successfully obtained mutants with obvious phenotypes of genes associated with body color, growth, intermuscular bone, and sex differentiation by CRISPR/Cas9 in O. macrolepis. Full article

The abundance, spatial distribution of and dynamic changes in ichthyoplankton species affect the recruitment and fish population dynamics, which are fundamental for stock assessment and fisheries management. An evaluation of alternative sampling designs needs to be carried out to determine the optimal scheme that is cost-effective in collecting high-quality ichthyoplankton data. A simulation study was conducted to evaluate the performances and consistency of six potential sampling designs for an ichthyoplankton survey in the coastal waters of the central and southern Yellow Sea. Relative estimation error (REE) and relative bias (RB) were used to measure the performances in estimating the population abundances of five target ichthyoplankton species in different sampling designs. In general, the two systematic sampling (SYS) designs had high precision and accuracy estimation and remained stable over years for estimating the population abundance of ichthyoplankton species compared with the other four sampling designs. SYS did not result in the overestimation or underestimation of the mean population abundance. Most sampling designs showed relatively high accuracy in abundance estimation when sample sizes were higher than medium levels. This study could improve the performances of sampling designs of ichthyoplankton surveys and provide a reference for the further optimization of sampling designs. Full article

Taurochenodeoxycholic acid (TCDCA), one of the bile acids, is thought to be involved in the regulation of muscle nutrient metabolism and gut microbial homeostasis. However, the effect of dietary addition of TCDCA on Procambarus clarkii is unclear. Therefore, in this study, an 8-week feeding experiment was conducted to explore the potential regulatory mechanisms of TCDCA on P. clarkii growth, physiology, muscle quality and gut microbes. The results indicated that dietary addition of TCDCA not only improved growth performance (final weight; weight gain; and specific growth rate) but also increased muscle elasticity and protein content. In addition, dietary TCDCA promotes muscle growth and development by increasing myofiber length, which is consistent with the activation of the expression of genes related to protein utilization (TOR and AKT) and muscle proliferation and differentiation (MyHC, MLC1, MEF2A, MEF2B). Importantly, 16s rRNA sequencing demonstrated that dietary TCDCA had no significant effect on gut microbial composition (alpha diversity) but significantly increased microbial abundance at the genus level. Functional prediction analysis of differential microbes revealed that dietary TCDCA may promote metabolism by altering gut microbes, thereby promoting muscle quality. In conclusion, our study demonstrates that the dietary addition of TCDCA promotes P. clarkii growth and muscle quality and protein deposition by altering gut microbes. Full article

Stress is recognized as an adaptive response to potentially harmful environmental stimuli. The primary physiological adaptation to stress is an increase in circulating cortisol levels, which, in excess, can be transferred and incorporated into the oocytes of maturing females, affecting the embryonic developmental program. Additionally, maternal energy availability is an essential environmental factor that modulates this program. Based on this background, we investigated the effects of maternal cortisol on the development of the somatotropic axis in zebrafish offspring and juveniles. Zebrafish mothers were divided into two groups based on diet: Group 1 received a cortisol-enriched diet, to mimic maternal stress, while Group 2 (control) received a standard diet, for five days. On the third day after treatment, the control and treated females were bred with untreated males. Offspring were assessed at 0, 24, 48, 72, 96, 120, and 144 h post-fertilization (hpf). Morphological analyses were performed during embryonic development, including survival rate, body length, the presence of pericardial edema, and heartbeat. We examined the gene expression of key somatotropic axis components, including mtor, foxo3a, mafbx, murf1, mstna, gh, igf1, igf2a, igf2b, 11hsdb2, and fkbp5. The study demonstrated that cortisol-treated females significantly influenced offspring development, resulting in higher mortality rates and increased morphological abnormalities, particularly pericardial edema. Gene expression analysis revealed alterations in transcripts related to the somatotropic axis, especially genes involved in protein synthesis, with signs of accelerated growth in the first hour post-fertilization. At 30 days post-fertilization, juveniles from cortisol-treated females displayed a marked increase in muscle bundle size and cross-sectional diameter compared to the control group. Our findings provide valuable insights into the intricate interaction between maternal factors and the development of the somatotropic axis in offspring. Full article