Fishes, Volume 9, Issue 3 (March 2024) – 32 articles

Commercial harvesting of snow crabs (Chionoecetes opilio) began in Newfoundland and Labrador, Canada, in 1967. Today, the fishery consists of 2188 active fishing licenses and has grown into the province’s most economically valuable fishery. Snow crabs are captured using conical traps consisting of a mild carbon steel frame, hard plastic entry funnel and a jacket of polyethylene netting. The frames of these traps corrode over time, which is expedited by being deployed in marine environments and stored on land near the ocean when not in use. As a result, there is interest within the community to increase the longevity of crab traps. One solution is to galvanize the steel frames prior to installing the funnel and netting. However, before harvesters transition to galvanized traps, two questions must be answered. Will the use of galvanized steel negatively impact catch rates? Will the life cycle of a crab trap be extended sufficiently to justify the additional cost of galvanizing? This study employed a generalized linear mixed model to evaluate the catch of legal-sized male crabs (CPUE) during the commercial fishery as a function of three trap frame treatments (old traditional, new traditional and new galvanized). We also assessed the economic viability of galvanizing trap frames by evaluating the life cycle cost (LCC) of traditional and galvanized traps to the harvester. The LCC was calculated over a range of inflation (0–6%) and discount (3–20%) rates. Our results found no significant difference in CPUE between new traps (traditional vs. galvanized) and concluded that except during instances of very high discount rates (12.9–19.9%), it is economically favourable to galvanize crab trap frames. Full article

A study was conducted to test the inclusion of Aurantiochytrium sp. meal in the rearing of Penaeus vannamei grown in a clear water system and at a suboptimal temperature of 22 °C. The doses tested were 0 (control), 1, 2, 3, and 4% at a stocking density of 100 shrimp/m³. Rearing was carried out with aeration and individual heaters, and seawater temperature was controlled with a chiller. After nine weeks, shrimp were weighed and hemolymph was collected for hemato-immunological tests, and growth performance were calculated. Shrimp raised at 22 °C and fed a 1% of dietary supplementation of Aurantiochytrium sp. meal were superior in immunological parameters. After the dietary assay, a total of 42 shrimps (10.9 ± 0.06 g) per treatment were infected with White Spot Syndrome Virus (WSSV). They were orally infected with 2.6 ± 10⁶ virus particles per g of the animal, maintained at a suboptimal temperature of 22 °C for 108 h, and acclimated to an optimal temperature of 28 °C for an additional 48 h. At 7 days post infection, surviving shrimp were collected for hemato-immunological analysis. Cumulative mortality results showed that shrimp fed diets containing 3% and 4% Aurantiochytrium sp. meal had higher survival than other treatments when challenged with WSSV. Full article

Data from the fishery of S. oualaniensis in the northern Indian Ocean from January to March and October to December 2017 to 2019 were modeled with sea surface temperature (SST), wind speed (WS), and photosynthetically active radiation (PAR). In this study, the fishing effort was used to evaluate the suitability index (SI) at SST, WS, and PAR. An integrated habitat suitability model (HSI) was developed with different weighting scenarios and weighting schemes. The optimal case was selected by calculation and comparison with the proportion of catch, effort, and catch per unit effort (CPUE) in the HSI interval (0~0.2, 0.2~0.6, 0.6~1); validation was performed using data from 2019. The weight of the optimal HSI model was 0.25 for sea surface temperature and photosynthetically active radiation, and 0.5 for wind speed. This model yielded the best performance and could accurately predict the fishing ground of S. oualaniensis in the northern Indian Ocean. The findings suggest that the integrated HSI model can predict the distribution of S. oualaniensis commendably, with wind speed as the most important factor affecting the spatial distribution of S. oualaniensis’ habitat in the northern Indian Ocean. By analyzing habitat selection by S. oualaniensis, this study verified and predicted the distribution of squid in the northern Indian Ocean, which allows the distribution of squid resources and fishing grounds to be modeled, and for the sustainable use of squid fishery resources. Full article

Modeling individual growth in marine species for aquaculture encounters many difficulties when the species pauses its growth but resumes its later after the disrupting phenomenon (environmental or physiological) has been overcome. Seasonal or oscillatory growth has been addressed by modifying existing models, such as von Bertalanffy and Gompertz, to include an oscillatory component in this study. The novelty of this study lies in the fractal approach used to analyze growth using multiple logistic functions. Three commercially farmed marine species were studied, including shellfish, crustacea, and finfish. The oscillatory version of the von Bertalanffy model as well as double and triple logistic functions were used for analysis. The best model was selected using the information theory, Specifically the Akaike criterion (AIC) and the Bayesian criterion (BIC). Normal and log-normal distributions of error were assumed. The triple logistic model with log-normal distribution in the error structure was found to be the best model to describe the growth pattern of the three commercially farmed species as it obtained the lowest AIC. Overall, this study concludes that the fractal approach is the most effective way to describe growth in farmed species, including shellfish, crustacean, and finfish. Full article

Metamorphosis is a crucial process in the life cycle of Rana (Aquarana) catesbeiana. R. catesbeiana tadpoles, in their short larval period, possess a high survival rate and also a highly competitive ability in the amphibious stage. In actual seed production, the economic traits of larval period and metamorphosis rate are used as quantifiable indicators of quality for individuals and populations, respectively. However, studies of these economic traits in larval cultivation and production are still lacking. In this study, we constructed 40 full-sib families of R. catesbeiana and measured the weight and metamorphosis rate of tadpoles at different developmental stages. Subsequently, we calculated the phenotypic and genetic association between weight and metamorphosis rate in tadpoles and assessed the heritability of these two traits. The heritabilities of weight at three developmental stages were all higher than 0.40 and decreased with advancement of the developmental stage; the heritability of the metamorphosis rate was 0.18 ± 0.20, a moderate level. Correlation analysis of weight and metamorphosis rate at each developmental stage in each tadpole family showed that weight at stages 25-I, 25-II, and 25-III was significantly correlated at the phenotypic level but non-significantly at the genetic level. The metamorphosis rate was only moderately associated with stage 25-III weight (0.38, p < 0.05). The results of this study confirm the importance and transportability of tadpole weight in actual seed production and provide basic data and a potentially optimized direction for the selective breeding of high-metamorphosis-rate bullfrogs. Full article

The assessment of the economic impacts of marine invasive species is fundamental for adopting mitigation measures, yet such impacts have been underreported in the Mediterranean Sea. The silver-cheeked toadfish (Lagocephalus sceleratus) is a toxic pufferfish that since its introduction has seriously disturbed small-scale fisheries along the eastern Mediterranean coast. This species depredates on fishing gears, causing damage to nets, longlines and commercial catches. To quantify its economic impact on small-scale fisheries, we interviewed 141 fishers from Crete (Cretan and Libyan Sea) and the Ionian Sea (Greece) during May 2020–December 2022. The mean annual economic cost resulting from L. sceleratus depredation was estimated at EUR 6315 ± 2620 per vessel in Crete and EUR 258 ± 120 in the Ionian Sea. Additionally, observer surveys carried out on board small-scale fishing vessels in Crete showed that depredation probability was significantly influenced by fishing depth, sea surface temperature, gear type (nets, longlines) and region (Cretan, Libyan Sea). L. sceleratus was caught more frequently and in higher numbers in the Libyan Sea. In response to depredation, fishers in Crete have altered their fishing tactics in terms of fishing in deeper waters, reducing fishing time and changing the technical characteristics of fishing gears. Our results underscore the adverse impacts of L. sceleratus on Greek small-scale fishers, emphasizing the need for region-specific management plans where the species establishes large populations. Full article

Prior aquatic animal image classification research focused on distinguishing external features in controlled settings, utilizing either digital cameras or webcams. Identifying visually similar species, like Short mackerel (Rastrelliger brachysoma) and Indian mackerel (Rastrelliger kanagurta), is challenging without specialized knowledge. However, advancements in computer technology have paved the way for leveraging machine learning and deep learning systems to address such challenges. In this study, transfer learning techniques were employed, utilizing established pre-trained models such as ResNet50, Xception, InceptionV3, VGG19, VGG16, and MobileNetV3Small. These models were applied to differentiate between the two species using raw images captured by a smartphone under uncontrolled conditions. The core architecture of the pre-trained models remained unchanged, except for the removal of the final fully connected layer. Instead, a global average pooling layer and two dense layers were appended at the end, comprising 1024 units and by a single unit, respectively. To mitigate overfitting concerns, early stopping was implemented. The results revealed that, among the models assessed, the Xception model exhibited the most promising predictive performance. It achieved the highest average accuracy levels of 0.849 and 0.754 during training and validation, surpassing the other models. Furthermore, fine-tuning the Xception model by extending the number of epochs yielded more impressive outcomes. After 30 epochs of fine-tuning, the Xception model demonstrated optimal performance, reaching an accuracy of 0.843 and displaying a 11.508% improvement in predictions compared to the model without fine-tuning. These findings highlight the efficacy of transfer learning, particularly with the Xception model, in accurately distinguishing visually similar aquatic species using smartphone-captured images, even in uncontrolled conditions. Full article

Hong Kong oysters (Crassostrea hongkongensis) are an important marine bivalve with nutritional and commercial value. The expanded off-bottom farming scale in recent years makes the oysters more susceptible to exposure to abiotic stresses, such as salinity stress, an important environmental factor that has been proven to have significant effects on oyster growth and development. However, the molecular mechanism is still unclear. Cyclin E is an important protein in the process of cell cycle regulation that is indispensable for propelling G1/S phase transition in a dose-dependent manner. In order to investigate whether the salinity stress affects cyclin E expression in oysters, the cDNA sequence of C. hongkongensis cyclin E (Ch-CCNE) was isolated from a gill cDNA library, and the 2.8 kbp length cDNA fragment contained a complete open reading frame (ORF) encoding 440 amino acid residues. Ch-CCNE mRNA was highly expressed in the gonad and low in the adductor mussel, mantle, gill, labial palp, and digestive gland. The recombinant CCNE protein was expressed and purified in a pET32a(+)-CCNE/Escherichia coli BL21(DE3) system via IPTG induction and was used for generating mice anti-Ch-CCNE antiserums. Western blot analysis showed that the CCNE protein in the gill was maintained at low expression levels under either hypo- (5 ppt) or hyper- (35 ppt) salinity, and could be produced at high levels under appropriate salinity during a 10-day exposure period. The immuno-localization indicated that the Ch-CCNE protein was distributed in the nucleus. These results suggested that either hypo- or hyper-salinity stress could inhibit the CCNE expression of Hong Kong oysters and their negative impact on cell division and proliferation. Full article

The research aimed to analyze the influences of adding marine green algae Chaetomorpha aerea to the diet of guppy fish (Poecillia reticulate) on growth, immunological responses in skin mucus, total carotenoid content, and sexual characteristics. A total of 450 fish, with a mean body weight of 0.19 ± 0.1 g and 30 fish per tank (triplicate), were randomly fed into 15 experimental tanks, each containing 50 L. Five different diets with 0, 1, 2, 4, 8, and 10% of C. aerea g/kg diets were fed to P. reticulate for 30 days. After 30 days, growth, immunological responses in skin mucus, total carotenoid content, and sexual characteristics were investigated. The results observed that the feed conversion rate and fry output were significantly (p > 0.05) decreased in experimental groups compared to the control group. The results revealed that the dietary inclusion of C. aerea algal significantly increased (p < 0.05) in mucosal immunological parameters containing lysozyme activity, myeloperoxidase activity, total immunoglobulins, and alternative complement activity, which were the highest in the group with 4% of C. aerea g/kg. Additionally, lateral skin and the caudal fin of fish had higher total carotenoid levels from the dietary C. aerea algae diet than the control group, which were the highest in the groups with 4%. Among them, 4 and 8% of C. aerea g/kg diet resulted in better growth performance and feed conversion ratio. Thus, the study suggested that 4% of C. aerea g/kg diet has enrichment of immunity, total carotenoid concentrations, and skin mucus immunity of P. reticulate. Full article

Yellow catfish (Pelteobagrus fulvidraco) is an important freshwater fish species in aquaculture. However, as intensive farming has rapidly expanded, infectious diseases caused by various bacteria, such as Aeromonas hydrophila, have also increased. We conducted a transcriptomic analysis of head kidney from P. fulvidraco stimulated by A. hydrophila strain SHOU. A total of 43,249 unigenes with an average length of 1342 bp were obtained following assembly and annotation. By analyzing GO and KEGG enrichment, many differentially expressed genes (DEGs) and pathways related to immunity were identified. Out of the 973 DEGs that were identified, 553 were upregulated and 420 were downregulated. Moreover, KEGG enrichment analysis revealed that the innate immune system, including the TNF signaling pathway, NF-kappa B signaling pathway, and the Toll-like receptor signaling pathway involved in the defense, is activated against infectious response. Real-time quantitative reverse transcription-PCR (qRT-PCR) analysis demonstrated that immune response genes were upregulated in response to A. hydrophila stimulation compared to the control. In conclusion, this study provides valuable insights into the immune defense mechanism of P. fulvidraco and sheds light on the host immune genes involved in the response to bacterial infection. Full article

Increased infectious diseases and the reduced effectiveness of antibiotics due to antimicrobial resistance pose global challenges affecting the aquaculture industry. As bacteria increasingly develop antibiotic resistance, research scientists are shifting their focus to technologies such as antimicrobial photodynamic therapy (aPDT), which show potential for treating and controlling fish infections without promoting the development of resistant bacteria. Various photosensitizers (PSs), both natural and synthetic, are under investigation for their application in aPDT within the aquaculture industry. This shift is crucial for the sustainability of the aquaculture industry, which plays a significant role in achieving several of the United Nations (UN) Sustainable Development Goals (SDGs). This review highlights the application of aPDT against fish pathogens in the industry and the types of PSs utilized. It also explores the potential application of this technique for treating and controlling fish infections, along with the advantages and limitations of its use in aquaculture production systems. Finally, a conclusion and future perspectives are provided. Full article

In recent years, micro- and nanoplastics (MNPs) have represented an emerging threat for the aquatic environment due to their persistence and widespread distribution. Indeed, their small size and increased surface area lead to a high biological reactivity, which can be crucial for the health status of biota. To date, several studies have investigated lethal and sublethal endpoints of MNPs, while one of the main challenges is to understand their mechanisms of toxicity in a comprehensive manner. With this aim, the field of aquatic ecotoxicology can now benefit from the -omics approaches. This review focuses on the recent advances related to the use of transcriptomics, proteomics, and metabolomics to deeply investigate the molecular and biochemical responses of aquatic organisms, both fishes and aquatic invertebrates, to pristine polystyrene (PS) MNPs. The literature reviewed revealed that transcriptomics and metabolomics are the most frequently used -omic approaches. Overall, the studies taken into consideration shed light on the events triggered by PS MNPs at molecular and cellular levels, identifying as mechanisms of toxicity the pathways involved in oxidative stress, energy metabolism, immune response, and the nervous system. Future studies should therefore focus on the use and integration of multi-omics approaches for a more comprehensive understanding of the mechanisms involved in MNPs toxicity. Full article

Farming Chinese perch in aquaculture systems with artificial diets is a new method and developing trend. This method of raising Chinese perch has led to outbreaks of new diseases. In 2022, a disease outbreak occurred among farmed Chinese perch fed an artificial diet in Jiangxi Province, China, during which 50% of the fish died. The clinical signs exhibited by the diseased Chinese perch included decreased physical vitality, anorexia, emaciation, and dorsal fin ulceration with white cysts and flocs. Coinfection with ciliate parasites and an oomycete was found. No pathogenic bacteria were isolated from the microbial test, and the viral detection results were negative. After morphological and 18S or 28S rDNA sequence clustering analysis, the parasites were identified as Epistylis wuhanensis and Zoothamnium sp., while the oomycete was identified as Achlya klebsiana. This article discusses the interaction between parasitic and oomycete coinfections in Chinese perch from the perspective of the characteristics of Chinese perch raised with an artificial diet. The relationships between parasites, oomycete, and fish were also briefly discussed. This is the first report of the coinfection of Chinese perch with Epistylis wuhanensis, Zoothamnium sp. and Achlya klebsiana. Full article

The rabbitfish Siganus oramin is an important naturally caught and aquaculture fish species. Intestinal microbiota can affect the metabolism and immunity of fish, which is closely related to the habitat of the host. In this study, we collected the wild fry S. oramin from a natural sea area, and cultured them in outdoor and indoor ponds, respectively, and investigated the changes in serum biochemical indexes and intestinal microbial community in three different habitats. The results showed that compared with the wild population, the serum total protein content of the outdoor culture population increased significantly. The indoor culture population had significantly higher triglyceride and total cholesterol contents than that of the outdoor culture population. Additionally, the intestinal microbial richness indexes ACE and Chao1 of the cultured population were higher than those of the wild population, especially the indoor culture, but Shannon and Simpson had no obvious changes. The relative abundances of Firmicutes, Spirochaetae and Bacteroidetes increased in the outdoor culture population, but decreased in the indoor culture population; those of Proteobacteria and Cyanobacteria were completely the opposite. Some putative beneficial bacteria (Lactobacillus, Clostridium sensu stricto 1, and Intestinibacter) and harmful bacteria (Vibrio, Photobacterium, Desulfovibrio, Streptococcus) all decreased in the intestines of the cultured population when compared with the wild population, while Akkermansia and Faecalibacterium were enriched in the outdoor culture population. These results reveal that a change in habitat environment, whether an outdoor or an indoor pond, positively influenced the intestinal microbiota of the rabbitfish, which is beneficial to the healthy culture of the fish from the perspective of microbial community. Full article

Environmentally cued hatching is prevalent, diverse, and crucial to many animals’ survival. Fish embryos use a variety of chemical cues to initiate hatching to avoid potential predators, yet the function of chemical cues released from the predatory consumption of heterospecific prey is largely unknown. Zebra cichlids (Metriaclima estherae) are ferocious predators that can feed on medaka (Oryzias latipes), though it is impossible for this to occur in their natural habitat. Zebrafish (Danio rerio) embryos have been employed as experimental subjects due to their sensitivity to a variety of chemical signals. In this study, zebrafish embryos were subjected to three types of chemical signals: predator cues (PCs, released from cichlids), heterospecific cues (HCs, released from medaka), and heterospecific dietary cues (HDCs, released from cichlids that have ingested medaka). As a result, the hatching times of zebrafish embryos were accelerated by 6.8% and 12.6% by PCs and HDCs, respectively. PCs and HDCs cause significantly reduced morphology in zebrafish embryos, including regarding total length, eye length, dorsal fin length, trunk height, caudal fin height, and body cavity, and increase yolk sac height. The PCs and HDCs diminished the larvae’s motion at 120 and 144 h post fertilization (hpf), which could be attributed to non-developmental embryogenesis. Overall, the impacts of HDCs on embryonic hatching, developmental morphology, and locomotor were more pronounced in comparison with PCs. Our findings demonstrate that predators’ dietary cues, even those released after predation on heterospecific prey, can modify embryogenesis, highlighting the critical functions of chemical signals in predation risk assessment using embryos. Full article

This study presents a comprehensive analysis of the length-weight relationship, condition factors, and age of Schizothorax eurystomus in the Shakhimardan River basin in Central Asia, along with a comparative perspective to other Schizothorax species in the region. The study found that S. eurystomus exhibits positive allometric growth, which is consistent with similar patterns observed in this species from the Syr Darya River basin. The two analyzed condition factors showed mean values within the normal range, indicating good feeding and environmental conditions. However, significant disparities between minimum and maximum values of these factors indicated varied growth conditions which may be influenced by anthropogenic factors. Age estimation using opercular bones showed variations in the total length among fish of the same age, and a clear age distribution pattern across different sites. Younger fish predominantly inhabited the shallower, warmer, and lower sections of the river, which is impacted by agricultural water diversion, while older specimens were found in areas with higher discharge and deeper pools. Overall, this research provides valuable insights into the life history traits of S. eurystomus, underlining the need for sustainable fishery management and conservation strategies in the Shakhimardan River basin. The findings also emphasize the importance of considering habitat quality and anthropogenic pressures regarding understanding both fish population dynamics and growth patterns. Full article

In this study, the distribution patterns of southern horse mackerel are examined using commercial fine-scale resolution data. Using landings by size category and VMS data from the Portuguese commercial bottom-trawl fishery, which consistently targets horse mackerel, this study provides a comprehensive analysis of horse mackerel age distributions spanning a decade (2010–2020). Importantly, this study addresses potential biases in commercial effort data and establishes the usefulness of commercial bottom-trawl gear as a suitable method for sampling and evaluating southern horse mackerel stock dynamics. Ordered regression models were applied to allow for the modelling of the distribution of multiple age categories and investigate spatio-temporal migrations off the Portuguese coast. Southern horse mackerel show a widespread age distribution range and stable abundance with indications of seasonal and spatial patterns in the distribution of specific age groups. The insights derived from this research contribute valuable knowledge for understanding the dynamics and distribution patterns of fish populations. Full article

High temperatures are important environmental stressors affecting the metabolism, growth, immunity, and mortality of Chinese mitten crabs (Eriocheir sinensis). In this study, Chinese mitten crabs were divided into two groups and exposed to temperatures of 35 °C (thermal stress group) or 25 °C (control group) for 24 h, and the transcriptome of the heart was analyzed. There were 4007 differentially expressed genes (DEGs) between the thermal stress and the control groups, including 2660 upregulated and 1347 downregulated genes. Heat shock proteins (HSPs) and transcription factors (TFs) were temperature-sensitive DEGs in Chinese mitten crabs. DEGs mainly focused on protein processing in the endoplasmic reticulum, ribosome biogenesis, glycine, serine, and threonine metabolism, protein export, and insect hormone biosynthesis pathways. A total of 28,916 SSRs and 59 TF families, including 851 TFs, were detected among all unigenes of E. sinensis transcripts. The qRT-PCR results for the HSPs and apoptotic DEGs from the heart exhibited the same trends as those in the E. sinensis transcriptome data. Results of light microscopy analyzing histological sections of the heart indicated that most myocardial fibers were lysed, and the number of nuclei and the connective tissue contents between the myocardial layers were both reduced following 35 °C exposure for 24 h. Full article

Elizabethkingia miricola (E. miricola) is a significant pathogen that causes the crooked head disease in black spotted frogs. This disease has plagued numerous frog farms in China and has resulted in substantial losses to the frog farming industry. Nonetheless, the exact mechanism that causes the disease in frogs remains unknown. In this study, transcriptomic and microbiomic analyses were conducted to analyze frog samples infected with E. miricola to reveal the infection mechanism of the pathogen. Liver transcriptomic analysis indicated that the livers of infected frogs had 1469 differentially expressed genes when compared with an uninfected group. These DEGs are mainly involved in immunity and metabolism, including neutrophil extracellular trap formation, the NOD-like receptor signaling pathway, leukocyte transendothelial migration, chemokine signaling pathway, Fc gamma R-mediated phagocytosis, and “metabolism”-related pathways such as the pentose phosphate pathway, carbon metabolism, glycerophospholipid metabolism, and glycerolipid metabolism. Similarly, 4737 DEGs were found in the kidney of infected frogs. These DEGs are mainly involved in immunity, including neutrophil extracellular trap formation, the NOD-like receptor signaling pathway, B cell receptor signaling pathway, C-type lectin receptor signaling pathway, complement and coagulation cascade, and Toll-like receptor signaling pathway. Ten immune-associated DEGs were screened in liver and kidney DEGs, respectively. And it was hypothesized that E. miricola infection could influence the host immune response. Microbiome analysis results showed that some opportunistic pathogens such as Citrobacter, Shigella, and Providencia were significantly elevated (p < 0.05) in infected frogs. Additionally, functional prediction confirmed that most of the microbiota in infected frogs were linked to metabolism-related KEGG pathways. In this study, the screened genes linked to immunity showed an association with the gut microbiome. The majority of these genes were found to be linked with the abundance of opportunistic pathogens. The results showed that E. miricola infection led to the downregulation of immune and metabolic-related genes, which led to the inhibition of immune function and metabolic disorder, and then increased the abundance of opportunistic pathogens in the gut microbiota. The findings of this study offer a preliminary foundation for comprehending the pathogenic processes of E. miricola infection in black spotted frogs. Full article

Coilia nasus is a typical anadromous migratory fish found in the lower reaches of the Yangtze River. Every year, C. nasus clusters offshore and swims upstream along the Yangtze River into the tributaries and lakes in the middle and lower reaches of the Yangtze River to breed. In this study, female C. nasus were collected as study subjects from the Chongming section of Shanghai, the Taizhou section of Jiangsu, and the Anqing section of Anhui. Their ovaries were used to examine tissue sections and investigate gene expression, including the follicle-stimulating hormone receptor (fshr), the luteinizing hormone receptor (lhr), kisspeptin-1 (kiss1), and forkhead box l2 (foxl2), which are related to reproductive development, while the serum levels of estrogen (including estradiol, E2) and progestins (including 17α,20β-dihydroxy-4-pregenen-3-one, 17α,20β-DHP) were also analyzed. Our results showed that, first, the growth period of the oocytes was small in stage II of ovarian development, in which both E2 and 17α,20β-DHP levels and gene expression were low. Then, in stage III, the growth period of the oocytes became large, and the yolk granules and oil droplets began to appear. Simultaneously, E2 and the expression of kiss1 and foxl2 were significantly elevated. Finally, stage IV was the period of a large amount of accumulation of nutrients in the oocytes, and 17α,20β-DHP levels and the expression of fshr and lhr were significantly elevated. These results enrich the theoretical study of ovarian development in the natural population of C. nasus, supplementing the biological basis of C. nasus reproduction and scientifically supporting the study of C. nasus population ecology and resource conservation. Full article

Genetic composition plays a crucial role in the growth rate of species, and transcriptomics provides a potent tool for studying genetic aspects of growth. We explored the growth rates and transcriptomes of the Cyprinids G. przewalskii (GP) and G. eckloni (GE). A total of 500 individuals of G. przewalskii and G. eckloni, matched in size, were separately cultured for 9 months in six cement tanks (each group with three replicates). Growth indices were measured, revealing that the growth rate of GE was greater than that of GP (p < 0.05), while there was no significant difference in survival rates (p > 0.05). Simultaneously, we conducted RNA-Seq on the muscles of both GP and GE. The results indicated a significant difference of gene expression between GP and GE, identifying 5574 differentially expressed genes (DEGs). Quantitative real-time reverse transcription–polymerase chain reaction of 10 DEGs demonstrated consistency in expression profiles with the results from the RNA-Seq analysis. The DEGs were significantly enriched in glycolysis/gluconeogenesis (ko00010), arachidonic acid formation (ko00061), arginine biosynthesis (ko00220), and the MAPK (ko04013), PI3K-Akt (ko04151), mTOR (ko04150), and TGF-β (ko04350) signal pathways, as revealed by Gene Ontology (GO) enrichment and the Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis. This study also identified some growth-related DEGs, such as IGF2, Noggin, Decorin and others. Notably, the low expression of IGF2 may be a factor contributing to the slower growth of GP than GE. Full article

Excessive flow turbulence poses a threat to the development of drifting fish eggs, leading to mortality or developmental malformations and ultimately depleting early fish resources. Currently, there is a scarcity of quantitative studies investigating the effects of flow turbulence on the entire process of drifting fish egg development, from fertilized egg division to hatching. In this paper, the effects of different flow turbulence conditions (FTCs), including turbulent kinetic energy and shear stress, and action times on different stages of fish egg development were quantitatively explored using a transverse-oscillating-grids turbulence tank. Empirical formulas were established to predict the proportion of normal fish egg development under different FTCs within a selected range. The research findings provide a quantitative basis for protecting early fish resources, mitigating the biological invasion of specific fish, constructing fish-breeding facilities, and ensuring safe transfer and transportation. Full article

The taxonomy and geographical distributions of Osteobrama species have historically posed challenges to ichthyologists, leading to uncertainties regarding their native ranges. While traditional taxonomy has proven valuable in classification, the utility of an integrated approach is restricted for this particular group due to limitations in combining information from biogeography, morphology, and genetic data. This study addresses the taxonomic puzzle arising from the recent identification of Osteobrama tikarpadaensis in the Mahanadi and Godavari Rivers, casting doubt on the actual distribution and systematics of both O. tikarpadaensis and Osteobrama vigorsii. The research reveals distinctions among specimens resembling O. vigorsii from the Krishna and Godavari riverine systems. Notably, specimens identified as O. vigorsii from the Indian Museum exhibit two pairs of barbels, while those from the Godavari River in this study are identified as O. tikarpadaensis. Inter-species genetic divergence and maximum likelihood phylogeny provide clear delineation between O. vigorsii and O. tikarpadaensis. The study suggests that O. vigorsii may be limited to the Krishna River system in southern India, while O. tikarpadaensis could potentially extend from the Mahanadi River in central India to the Godavari River in southern India. Proposed revision to morphological features for both species, accompanied by revised taxonomic keys, aim to facilitate accurate differentiation among Osteobrama congeners. The data generated by this research provide a resource for future systematic investigations into cyprinids in India and surrounding regions. Further, the genetic diversity information obtained from various riverine systems for Osteobrama species will be instrumental in guiding aquaculture practices and formulating effective conservation action plans. Full article

As the largest lake in South China, Wanlv Lake is also an important drinking water source for Guangdong and Hong Kong and is responsible for water supplying of more than 40 million people in the Guangdong-Hong Kong-Macao Greater Bay Area. The study of fish diversity in Wanlv Lake can help us to effectively understand the changes and states of its aquatic ecosystem and provide scientific basis for natural ecological protection, biodiversity, sustainable use and scientific management of fishery resources. However, research on the lake’s fish is scarce. The high throughput environmental DNA metabarcoding technology (eDNA technology) of the mitochondrial 12S rRNA gene sequence was herein used to conduct a preliminary exploration of Wanlv Lake fish diversity. A total of 10 sampling sites were set up to monitor fish diversity and analyze the composition and richness of the species. The results revealed a total of 83 genera in 42 families and 17 orders of fish in the lake, with the highest proportion found in Cypriniformes (38 species), accounting for 45.24% of the total. Five alien species and eight rare and endangered species were also detected. The proportion of invasive species was 5.95%, and the combined proportion of rare and endangered species was 9.52%. The results indicated that Wanlv Lake serves as an important drinking water source, and overall, the condition of fish is satisfactory. However, proactive measures should be implemented to control the overpopulation of invasive species, as their unchecked proliferation may lead to a decline in species abundance, particularly among endangered species. This was the first overall assessment report on fish of the Wanlv Lake via 12S rRNA; the results herein lay a foundation for water quality assessment of Wanlv Lake as a drinking water source. Full article

Antibiotics are the primary measures employed in the prevention and treatment of diseases in aquaculture. However, the frequent utilization of antibiotics can significantly impact the growth and reproduction of aquatic organisms, resulting in water pollution. The European Union (EU) has prohibited antibiotic additives in animal feed. Potassium diformate (KDF) represents the first non-antibiotic feed additive approved by the EU as a viable alternative to antibiotics. Its application in animal nutrition has been validated, demonstrating beneficial health effects. This article reviews the physicochemical properties, biological functions, synthesis conditions, and applications of KDF in aquaculture and looks toward to its future potential. It also provides insights into improving the utilization of KDF in aquaculture practices. Full article

This study specifically focused on Litopenaeus vannamei and examined the distribution of residual antibiotics in various components of shrimp ponds throughout an aquaculture cycle. The findings revealed that aquaculture feed served as the primary source of antibiotics, continuously introducing them into the ponds throughout the entire production cycle. A multimedia distribution model for antibiotics in the ponds was established based on the principle of mass balance. The distribution characteristics of six antibiotics with higher levels in the feed, namely, sulfamethoxazole (SMX), norfloxacin (NOF), levofloxacin (LEOF), tetracycline (TC), oxytetracycline (OTC), and chlortetracycline (CTC), were investigated in the pond water, sediment, and shrimp. At the end of the cultivation period, the total antibiotic residues accounted for 65~80% in various media, with the sediment containing 50~60% of the distribution proportion (p < 0.01), which was identified as the primary reservoir for most antibiotics, with LEOF and NOF accounting for the highest proportions (45.78% and 50.29%, respectively). Based on the model’s findings and the allowable daily dosage of antibiotics, recommendations were made for the effective control of antibiotic residues in shrimp farming management. To address the significant net loss of sulfonamides (SAs) and tetracyclines (TCs) in aquaculture production, it is crucial to carefully regulate their dosages and administration methods. Implementing eco-friendly additives and regularly cleaning surface sediments can aid in reducing antibiotic residue levels in various environmental media, thereby mitigating the environmental impact on aquaculture production activities. Full article

Collichthys lucidus is a small fish found in offshore waters that is economically important for China. It is imperative to understand its distribution characteristics and driving factors. Based on survey data of trawl fishery resources offshore of Zhejiang province, China, in spring (April) and autumn (November) from 2018 to 2022, the spatial and temporal distributions of C. lucidus in this area were analyzed. The random forest (RF) model was used to determine the important marine factors affecting the distribution of C. lucidus. The relationship between the distributions of the important variables was analyzed. The results showed that C. lucidus was mainly distributed in coastal waters. The tail density of the species exhibited obvious seasonal variation and was significantly greater in autumn than in spring. The most important factor affecting the distribution of this species in spring and autumn was water depth. The bottom temperature, bottom salinity and dissolved oxygen concentration were also important influencing factors. The importance of these factors differed among the different seasons, while the chlorophyll a concentration and pH had no significant effect on the species distribution. This study revealed the distribution pattern of C. lucidus in offshore waters of Zhejiang Province and the influence of important marine factors on its distribution. This study can enrich the survey data on C. lucidus and provide basic data for its scientific management and protection. Full article

The effects of the intensification on the performance of the Amazon River prawn hatchery carried out in a simple recirculation system were investigated. Newly hatched larvae were stocked in 120 L tanks at 80, 100, 120 and 140 larvae L⁻¹ in a closed recirculating system. The experiment used a randomized block design with five replicates. An exponential equation was adjusted to express the relationship between the stocking density and productivity (postlarvae L⁻¹). The development, larval quality, survival and postlarval (PL) dry weight did not significantly differ among the treatments (p > 0.05). When 80 larvae were stocked, the productivity (54 ± 11 PL L⁻¹) was lower than those at higher densities (p < 0.05). Stocking 120 and 140 larvae L⁻¹ resulted in higher productivities (75 ± 18 and 80 ± 17 PL L⁻¹, respectively) with a lower use of Artemia nauplii to produce each postlarvae (~1200 Artemia nauplii PL⁻¹). The maximum mean M. amazonicum postlarval production estimated by the exponential model was 93 PL L⁻¹. This means that despite the increase in stocking density, productivity tends to stabilize. The results showed that M. amazonicum tolerates high intensification in recirculating hatchery systems based on a crushed shell bed biofilter, and the intensification optimizes Artemia use. Full article

We introduce a novel method that combines satellite data, advanced clustering techniques, machine learning feature extraction, and statistical models to enhance fishery forecasting accuracy. Focusing on jumbo flying squid in the southeast Pacific Ocean near Peru, we utilize MODIS-Aqua and MODIS-Terra satellite data on sea surface temperature (SST) to construct a deep convolutional embedded clustering (DCEC) model and extract the monthly SST features ($F_M)$ based on an optimized number of clusters determined by the Davies–Bouldi index (DBI). We use the extracted $F_M$ to construct a series of Generalized Additive Models (GAM) to forecast the catch per unit effort (CPUE) of jumbo flying squid within a spatial resolution of 0.5° × 0.5°. Our results demonstrate the following findings: (1) The SST feature clusters obtained through the DCEC model could capture the SST monthly variations; (2) The GAM models with $F_M$ outperform the models with the traditional monthly average SST in terms of predictive accuracy; (3) Using both $F_M$ and average SST together can further improve model performance. This study demonstrates the effectiveness of the DCEC combined with DBI in extracting marine environmental features and highlights the ocean environment feature extraction method to enhance the precision and reliability of fishery forecasting models. Full article

The use of artificial substrates and biofloc technology can favor fish culture and improve water quality. The aim of this study was to evaluate whether artificial substrates and carbon source additions modify the microbial activity of water bodies. The diversity and structure of microflora in the water after adding artificial substrates and carbon sources to the ponds were analyzed using high-throughput sequencing based on the V3-V4 region of 16S rRNA genes. The results showed that there was no difference in the richness and diversity of intestinal microflora between the control and experimental groups. Principal coordinate analysis (PCoA) and nonmetric multidimensional scaling (NMDS) showed that artificial substrate and carbon source addition changed the structure of the microflora. The results of a linear discriminant analysis (LDA) effect size (LefSe) indicated 11 biomarkers in the EGˍst group. Spearman correlation heatmap analysis showed that environmental factors affected the bacterial communities, and the results of a redundancy analysis indicated that chemical oxygen demand was a critical factor in controlling the bacterial communities in the water. These results provide an understanding of the effect of artificial substrate and carbon source addition on bacterial diversity and community composition in water. Full article