Aquaculture Breeding Research Articles

GRAMMAR-Lambda Delivers Efficient Understanding of the Genetic Basis for Head Size in Catfish

The shape of the skull plays a crucial role in the evolution and adaptation of species to their environments. In the case of aquaculture fish, the size of the head is also an important economic trait, as it is linked to fillet yield and ornamental value. This study applies our GRAMMAR-Lambda method to perform a genome-wide association study analysis on loci related to head size in catfish. Compared with traditional GWAS methods, the GRAMMAR-Lambda method offers higher computational efficiency, statistical power, and stability, especially in complex population structures. This research identifies many candidate genes closely related to cranial morphology in terms of head length, width, and depth in catfish, including bmpr1bb, fgfrl1b, nipbl, foxp2, and pax5, etc. Based on the results of gene–gene interaction analysis, we speculate that there may be frequent genetic interactions between chromosome 19 and chromosome 29 in bone development. Additionally, many candidate genes, gene families, and mechanisms (such as SOCE mechanisms) affecting skeletal development and morphology have been identified. These findings contribute to our understanding of the genetic architecture of head size and will support marker-assisted breeding in aquaculture, also reflecting the potential application of the GRAMMAR-Lambda method in genetic studies of complex traits.

Antibiotic Residues in Cultured Fish: Implications for Food Safety and Regulatory Concerns

Antibiotics are widely recognized as significant chemical pollutants that enter the environment and ultimately the food chain. They are extensively used in both aquaculture and terrestrial animal breeding. Antibiotic residues in cultured fish pose significant public health risks, including the potential for antimicrobial resistance and adverse health outcomes. This review examines the widespread use of antibiotics in aquaculture, highlighting key challenges such as the lack of reliable data on antibiotic consumption in many regions as well as variability in regulatory enforcement. While strict regulations in European countries help to mitigate risks, the growing, often unregulated use of antibiotics in low- and middle-income countries exacerbates concerns over food safety. This paper provides an in-depth analysis of global regulatory frameworks and the impact of antibiotic residues on public health, and it offers recommendations for improving the monitoring, regulation, and responsible use of antibiotics in aquaculture in order to ensure safer food products from farmed fish. It contributes to a deeper understanding of the global scope of antibiotic misuse in aquaculture and points to an urgent need for more effective management practices.

Characterization of the sex determining region and development of a molecular sex identification method in a Salangid fish

BackgroundThe short-snout icefish, Neosalanx brevirostris, a member of the Salangidae family, is an economically important fishery species in China. Understanding the mechanisms underlying sex determination in this species has crucial implications for conservation, ecology and evolution. Meanwhile, there is a shortage of rapid and cost-effective genetic methods for sex identification, which poses challenges in identifying the sex of immature individuals in sex determination mechanism studies and aquaculture breeding applications.ResultsBased on whole genome resequencing data, sex-specific loci and regions were found to be concentrated in a region on chromosome 2. All sex-specific loci exhibited excess heterozygosity in females and complete homozygosity in males. This sex determining region contains seven genes, including cytochrome P450 aromatase CYP19B, which is involved in steroidogenesis and is associated with 24 sex-specific loci and two W-deletions. A haploid female-specific sequence was identified as paralogous to a diploid sequence with a significant length difference, making it suitable for rapid and cost-effective genetic sex identification by traditional PCR and agarose gel electrophoresis, which were further validated in 24 females and 24 males with known phenotypic sexes.ConclusionsOur results confirm that N.brevirostris exhibits a female heterogametic sex determination system (ZZ/ZW), with chromosome 2 identified as the putative sex chromosome containing a relatively small sex determining region (~ 48 Kb). The gene CYP19B is proposed as a candidate sex determining gene. Moreover, the development of PCR based method enables genetic sex identification at any developmental stage, thereby facilitating further studies on sex determination mechanisms and advancing aquaculture breeding applications for this species.

Breeding evaluations in aquaculture using neural networks

Deep learning comes with a portfolio of highly flexible models, known as neural networks (NNs), capable of solving various problems and setting new high standards for prediction accuracy. Nevertheless, whether NNs could be of value in aquaculture selective breeding settings is unclear as the whole topic is underexplored. Furthermore, fine-tuning a plethora of hyperparameters before fitting a neural network is a daunting task. Using simulated and a publicly available dataset on genetic resistance in carp against koi herpes virus (KHV), various neural network architectures were benchmarked against commonly used animal breeding models. More specifically, the simulated datasets comprised 36000 phenotyped animals genotyped for 54000 single nucleotide polymorphisms (SNPs). In contrast, the carp dataset included 1255 carp juveniles with survival recordings for KHV that were genotyped for 15615 SNPs. The assessed NN architectures included multilayer perceptrons (MLPs), convolution neural networks (CNNs) and local convolution neural networks (LCNNs). In addition, the effect of various hyperparameters of neural networks, such as the number of hidden layers, neurons per layer, activation function, learning rate, batch size, and regularisation techniques like dropout, were examined. In the simulated datasets, fully connected models with 5 hidden layers and 100 neurons per layer performed slightly better (1 – 4 %) than ridge-regression best linear unbiased prediction (rrBLUP), while the CNNs gave the lowest prediction accuracies (∼ 14 % lower than MLPs) and the ones from LCNN in between the above (∼ 8 lower than MLPs). Nevertheless, the estimated breeding values from NNs appeared more biased than rrBLUP (mean regression slope of 1.2 for the NN with the highest prediction accuracy vs 1.08). A reverse picture was observed in the case of the carp dataset, where following the application of receiver operating characteristic (ROC) curves, the animal breeding models outperformed neural networks by more than 2 % (based on the area under the curve index). In this case the LCNN had the highest area under the curve index from all NNs. Overall, NNs could be valuable tools in aquaculture breeding programs, though large training datasets of tens of thousands or more of phenotyped and genotyped animals seem to be required.

Genome-wide characterization and comparative expression profiling of dual-specificity phosphatase genes in yellow catfish (Pelteobagrus fulvidraco) after infection with exogenous Aeromonas hydrophila.

Dual-specificity phosphatases (DUSPs) are crucial regulators in many mammals, managing dephosphorylation and inactivation of mitogen-activated protein kinases (MAPKs) and playing essential roles in immune responses. However, their presence and functions in teleosts, like the yellow catfish (Pelteobagrus fulvidraco), remain unexplored. In this study, eight pfDusp genes (pfDusp1-7 and pfDusp10) were identified in yellow catfish. We characterized their molecular features, conserved protein sequences, and chromosomal localization through genome-wide analyses, and we examined their expression patterns in immune responses. Our findings reveal two conserved motifs, Leu-Phe-Leu-Gly and Ala-Tyr-Leu-Met, within the DSPc domain of DUSP proteins. The genes were mapped across seven chromosomes without evidence of duplication. Comparative analysis showed high conservation of Dusp genes across vertebrates, with evolutionary analysis suggesting Dusp3 as a potential intermediate form. Dusp transcripts were significantly upregulated in the kidney post-A. hydrophila infection. These results suggest the involvement of Dusp genes in the immune response of yellow catfish to bacterial pathogens, providing insights into their evolutionary significance and potential applications in aquaculture and molecular breeding.

Take good care of your fish: fish re-identification with synchronized multi-view camera system

IntroductionFish re-identification (re-ID) is of great significance for fish monitoring and can contribute to aquaculture and fish breeding. Synchronizing information from different cameras is beneficial for optimizing re-ID performance.MethodsWe constructed the first underwater fish re-identification benchmark dataset (FS48) under three camera conditions. FS48 encompasses 48 different fish identities, 10,300 frames, and 39,088 bounding boxes, covering various lighting conditions and background environments. Additionally, we developed the first robust and accurate fish re-identification baseline, FSNet, which fuses information from three camera positions by extracting features from synchronized video frames of each position and combining the synchronized information.ResultsThe experimental results show that FS48 is universal and of high quality. FSNet has an effective network design and demonstrates good performance, achieving better re-identification performance by combining information from three positions, helping improve overall re-test accuracy, and evaluating the effectiveness of re-identification among detectors.DiscussionOur dataset will be released upon acceptance of this paper, which is expected to further promote the development of underwater fish re-identification.

The Impact of Exposure Dosage and Host Genetics on the Shedding Kinetics of Flavobacterium psychrophilum in Rainbow Trout.

Flavobacterium psychrophilum, the causative agent of bacterial cold water disease (BCWD), is one of the leading pathogens in rainbow trout (Oncorhynchus mykiss) aquaculture. To date, there is little knowledge of the transmission kinetics of F. psychrophilum over the course of infection. In particular, how transmission is affected by host genotype and pathogen exposure dosage are not well studied. In order to fill in these knowledge gaps, we exposed two divergently selected lines of rainbow trout (ARS-Fp-R and ARS-Fp-S) to a range of dosages of F. psychrophilum (strain CSF117-10). We then measured mortality and bacterial shedding to estimate transmission risk at multiple time points since initial infection. As dosage increased, the number of fish shedding and the amount of bacteria shed increased ranging from 0% to 100% and 103 to 108 cells fish-1 h-1, respectively. In addition, we found that disease resistance (survival) was not correlated with transmission risk blocking, in that 67% of fish which shed bacteria experienced no clinical disease. In general, fish mortality began on Day 3, peaked between Days 5-7 and was higher in the ARS-Fp-R line. Results from this study could be used to develop epidemiological models and improve disease management, particularly in the context of aquaculture and selective breeding.

Identification of growth-related genes based on BSA in Pacific white shrimp Litopenaeus vannamei

The development of SNP genotyping techniques has facilitated the application of genome-wide association studies (GWAS) and genomic selection (GS) in plants and animals. However, the cost of high-throughput SNP genotyping is particularly high in the case of aquaculture animals which can produce a large number of offspring. Consequently, a cost effective method for trait-associated SNP identification and application was urgently needed in aquaculture breeding. In this study, a Bulk Segregation Analysis sequencing (BSA-seq) method was employed to identify growth-related single nucleotide polymorphisms (SNPs) and genes in the Pacific white shrimp Litopenaeus vannamei. Two independent families were used for this analysis to reduce the false positive. The DNA of individuals with the highest and lowest body weights was pooled separately. Two methods including the ED (Euclidean distance) method and the chi-square test were applied to calculate the allele differences between high and low growth rate individuals. A total of 24,325,437 SNPs were identified and consequently 1,299 SNPs and 163 genes were identified to be associated with growth traits. KEGG enrichment analysis showed that these genes were significantly enriched in phosphatidylinositol signaling system and phospholipase D signaling pathway. The diacylglycerol kinase genes, phosphatidylinositol 3-kinase genes, inositol polyphosphate 5-phosphatase genes, mitogen-activated protein kinase genes, myotubularin-related protein genes and epidermal growth factor receptor genes in these pathways were considered as candidate growth genes. This study demonstrated that the BSA-seq based on whole genome resequencing is cost-effective and useful in aquaculture. The results not only provide useful information for understanding the genetic basis of growth traits, but also offer a source of SNPs for marker-assisted selection (MAS) and genomic selection (GS) in shrimp.

Chromosomal aberrations and early mortality in a non-mammalian vertebrate: example from pressure-induced triploid Atlantic salmon

In commercial aquaculture, the production of triploid fish is currently the most practical approach to prevent maturation and farm-to-wild introgression following escapes. However, triploids often exhibit poor welfare, and the underlying mechanisms remain unclear. Inheritance issues associated with sub-optimal hydrostatic pressure treatments used to induce triploidy, or the genetic background of parental fish, have been speculated to contribute. We tested this by quantifying the frequency and type of chromosomal aberrations in Atlantic salmon subjected to a gradient of sub-optimal pressure treatments (Experiment 1) and from multiple mothers (Experiment 2). From these experiments, we genotyped a subsample of ~900 eyed eggs and all ~3300 surviving parr across ~20 microsatellites. In contrast to the low frequency of chromosomal aberrations in the diploid (no hydrostatic pressure) and triploid (full 9500 PSI treatment) controls, eyed eggs subjected to sub-optimal pressure treatments (6500–8500 PSI) had a higher incidence of chromosomal aberrations such as aneuploidy and uniparental disomy, corresponding to lower triploidization success and higher egg mortality rates. We also observed maternal effects on triploidization success and incidence of chromosomal aberrations, with certain half-sibling families exhibiting more aberrations than others. Chromosomal aberrations were rare among surviving parr, suggesting a purge of maladapted individuals during early development. This study demonstrates that sub-optimal hydrostatic pressure treatments and maternal effects not only influence the success of triploidization treatments, but may also affect the incidence of chromosomal aberrations and early mortality. The results have important implications for aquaculture breeding programs and their efforts to prevent farm-to-wild introgression.

The mechanism of INO80D involved in chromatin remodeling regulating spermatogenesis in Chinese mitten crab (Eriocheir sinensis).

The INO80D protein, a component of the INO80 chromatin remodeling complex, plays a pivotal role in chromatin remodeling, gene expression, and DNA repair within mammalian sperm. In contrast to the condensed nuclear structure of mammalian sperm, Chinese mitten crab, Eriocheir sinensis, exhibits a distinctively decondensed sperm nucleus. The distribution and function of INO80D during the E. sinensis spermatogenesis were previously enigmatic. Our research endeavored to elucidate the distribution and function of INO80D, thereby enhancing our comprehension of sperm decondensation and the process of spermatogenesis in this species. Employing transcriptome sequencing, RT-qPCR, western blot analysis, and immunofluorescence techniques, we observed a pronounced upregulation of INO80D in the adult E. sinensis in comparison to the juvenile. The protein predominantly resides in the cellular nucleus, with high levels in spermatogonia and spermatocytes, less in stage I and III spermatids, and lowest in mature sperm. The results indicated that INO80D is initially instrumental in chromatin decondensation to facilitate gene accessibility and DNA repair during the early phases of spermatogenesis. Its role subsequently shifts to maintaining decondensed chromatin stability and genetic integrity during spermiogenesis. The sustained presence of INO80D during spermiogenesis is essential for the ultimate maturation of the decondensed sperm nucleus, imperative for preserving the unique decondensed state and the protection of genetic material in E. sinensis. Our study concludes that INO80D exerts a multifaceted influence on the spermatogenesis of E. sinensis, impacting chromatin decondensation, genetic integrity, and the regulation of early gene expression. This understanding could potentially improve crab breeding in aquaculture.

Optimizing Strategy for Whole-Genome Genotype Imputation in Scallops

Advancements in sequencing technologies have facilitated low-coverage whole-genome sequencing (lcWGS) for detecting millions of single nucleotide polymorphisms (SNPs) in large populations at low cost. The effectiveness of this approach relies on genotype imputation following lcWGS. While several imputation methods have been applied in human and other terrestrial animals, their performance in aquaculture organisms, particularly mollusks, remains unassessed. Mollusks contribute 70% of mariculture production in China and are characterized by high genetic polymorphism. In this study, we aimed to optimize reference panel construction and evaluate imputation strategies for SNP detection in two scallops, Chlamys farreri and Patinopecten yessoensis, both important bivalve species. High-coverage whole-genome sequencing (hcWGS) data were used to construct haplotype reference panels, and three imputation methods were applied: Beagle5.4, GLIMPSE2, and QUILT. QUILT outperformed other methods, achieving imputation quality scores (IQS) exceeding 0.930 in C. farreri and 0.946 in P. yessoensis, and yielded the highest number of imputed loci in both species. Furthermore, panel construction was optimized by adjusting for genotype quality (GQ) and minor allele frequency (MAF); we determined that a GQ threshold > 20 and an MAF threshold > 0.01 were optimal. We observed that imputation quality improved with increased sequencing depth, plateauing at 0.5×, and varied with sample size depending on the imputation method. A negative correlation was observed between imputation quality and the ratio of non-synonymous to synonymous substitution rates (Ka/Ks) across chromosomal segments, highlighting the influence of selection pressure on imputation efficacy. Collectively, our findings provide an optimized framework for SNP genotyping using lcWGS in scallops, with implications for aquaculture breeding and genetic research.

Genetic diversity of the Ruditapes decussatus and evidence of its hybridization with the alien R. philippinarum in the Western Mediterranean Sea

The introduction of alien species in marine ecosystems is often driven by the increasing demand of fishery resources. This is the case of the Manila clam (R. philippinarum), imported in Europe from Japan since the 1970s, to meet the growing demand for clams that the native species, the grooved carpet shell clam (Ruditapes decussatus), could not satisfy. Alien species introduction could threaten the genetic diversity and integrity of the native clam, also causing hybridization (i.e., gene flow from one species into the gene pool of another). Since R. philippinarum recently spread in a few important Mediterranean coastal areas, a combined approach based on morphological characteristics, length differences of two nuclear species-specific markers (ITS2, 5SrDNA) and the sequence of the mitochondrial gene cytochrome c oxidase subunit I (COI), was used to investigate the presence of hybrids in six Mediterranean wetlands (Sardinia, Italy). Eight individuals morphologically identified as R. decussatus were hybrids, having sequences specific to both R. decussatus and R. philippinarum in their nuclear DNA (ITS2 and 5SrDNA). Most of these individuals were found to be post-first generation (F1) hybrids indicating that F1-hybrids may be fertile. Secondly, to study the genetic diversity of R. decussatus in the Sardinian wetlands as well as in its whole distribution area, >380 new COI sequences from the eastern Atlantic Ocean and Mediterranean Sea were analysed along with those available from public databases. Mitochondrial COI data revealed variable haplotype and nucleotide diversities in different areas, which were not dependent on sample sizes. The aquaculture breeding activities and clam transplantation between different countries, along with the long pelagic larval dispersal and the commercial import of other bivalve species might have promoted gene exchange between different sites and thus higher diversity levels in a few wild populations. Our research, evaluating the genetic makeup of wild and hatchery stocks and clarifying the degree of hybridization, can contribute to develop further recommendations for conserving the genetic integrity of R. decussatus.

Nile Tilapia Farming and Diversity in Sub-saharan Africa: A Review

This paper examines Nile tilapia (Oreochromis niloticus) in Sub-saharan Africa, where the expansion of aquaculture farms has resulted in the escape of fish, including Nile tilapia, into natural water bodies. This has led to the mixing of escaped tilapia with native species. To successfully manage and conserve these mixed species, it is important to understand their morphogenetic features. This review analyzes different production systems and morphometric variations of Nile tilapia in Sub-Saharan Africa, providing insight into the underlying factors. This review was carried out by exploring published papers, reports and books to gather information on the subject. The results showed that Nile tilapia are cultured in various systems, depending on the economics, skills, infrastructure and environmental conditions of farmers. Sub-saharan Africa exhibits a significant morphometric diversity of Nile tilapia, which has been studied using traditional and geometric morphometric methods. Both in situ and ex situ conservation methods are recommended to preserve the diversity of Nile tilapia for future aquaculture breeding programs in the region.

Mapping the genetic basis for sex determination and growth in hybrid tilapia (Oreochromis mossambicus × O. niloticus)

Tilapia growth and sex are key traits for aquaculture. Elucidating their molecular mechanisms can enable molecular breeding and accelerate genetic gain. To uncover the genetic basis underlying these traits for molecular breeding, we generated an F2 family by crossing Mozambique and Nile tilapia. The growth and sex traits of 284 F2 fish were recorded at 150 days post hatch. These F2 individuals exhibited sexual dimorphism in weight, body shape, and lip thickness, and were genotyped with RAD-sequencing. A high-density linkage map, consisting of 22 linkage groups with 38,102 SNPs was constructed. Association mapping revealed that QTL containing the amhy gene from male Nile tilapia largely determined sex, modulated by minor-effect loci. For growth-related traits, QTL and association analyses discovered that body weight or total length was predominantly controlled by a large-effect locus, while body shape was determined by several minor-effect loci. Analysis of transcriptomics in the liver and muscle identified novel candidate genes, including dusp2, rtn4r, bhmt1, adamts12 and s100p, for growth. These findings provide tools for sex-specific molecular breeding and valuable information for understanding the genomic architecture of growth and body shape variation. Assessing the sex-specific effects on growth can further refine selective breeding in aquaculture.

Development and application of molecular markers in fisheries, aquaculture, and industry of representative temperate and tropical sea cucumbers: a review

Sea cucumber has emerged as a crucial economic species in aquaculture in China because of its remarkable nutritional and medicinal value. However, wild sea cucumber populations have experienced a decline due to overfishing and environmental factors, underscoring the urgent need for genetic resource conservation and biotechnology innovation within the sea cucumber aquaculture and breeding industry. The development of the sea cucumber industry is still impeded by challenges and difficulties. Nevertheless, significant progress has been made through the utilization of molecular markers, which have effectively addressed a number of fisheries and aquaculture issues. In recent years, diverse types of molecular markers including mitochondrial DNA, microsatellites, and SNP markers have been developed and extensively applied in various aspects of sea cucumber research. These markers play vital roles in genetic sex identification, germplasm resource evaluation, population structure assessment, as well as marker-assisted breeding in marine ranching and sea cucumber aquaculture and breeding industry. This review provides an overview of the fundamental principles, functions, and characteristics associated with various markers employed across various sea cucumber species while also discussing their applications within different aspects of the sea cucumber fisheries, aquaculture, and breeding industry.

Infection and intracellular transport of white spot syndrome virus require the ESCRT machinery in shrimp.

Viruses utilize the ESCRT machinery in a variety of strategies for their replication and infection. This study revealed that the interaction of ESCRT complexes with WSSV envelope proteins plays a crucial role in WSSV infection in shrimp. The ESCRT system is conserved in the shrimp Marsupenaeus japonicus, and 24 homologs of the ESCRT system were identified in the shrimp. WSSV exploits the ESCRT system for transport and propagation via the interaction of envelope proteins with host TSG101 and ALIX in an endosome pathway-dependent manner. Understanding the underlying mechanisms of WSSV infection is important for disease control and breeding in shrimp aquaculture.

Differentially expressed proteins and microbial communities of the skin regulate disease resistance to Chinese tongue sole (Cynoglossus semilaevis).

Vibriosis, caused by Vibrio, seriously affects the health of fish, shellfish, and shrimps, causing large economic losses. Teleosts are represent the first bony vertebrates with both innate and adaptive immune responses against pathogens. Aquatic animals encounter hydraulic pressure and more pathogens, compared to terrestrial animals. The skin is the first line of defense in fish, constituting the skin-associated lymphoid tissue (SALT), which belongs to the main mucosa-associated lymphoid tissues (MALT). However, little is known about the function of immunity related proteins in fish. Therefore, this study used iTRAQ (isobaric tags for relative and absolute quantitation) to compare the skin proteome between the resistant and susceptible families of Cynoglossus semilaevis. The protein integrin beta-2, the alpha-enolase isoform X1, subunit B of V-type proton ATPase, eukaryotic translation initiation factor 6, and ubiquitin-like protein ISG15, were highly expressed in the resistant family. The 16S sequencing of the skin tissues of the resistant and susceptible families showed significant differences in the microbial communities of the two families. The protein-microbial interaction identified ten proteins associated with skin microbes, including immunoglobulin heavy chain gene (IGH), B-cell lymphoma/leukemia 10 (BCL10) and pre-B-cell leukemia transcription factor 1 isoform X2 (PBX2). This study highlights the interaction between skin proteins and the microbial compositions of C. semilaevis and provides new insights into understanding aquaculture breeding research.

FishSNP: a high quality cross-species SNP database of fishes

The progress of aquaculture heavily depends on the efficient utilization of diverse genetic resources to enhance production efficiency and maximize profitability. Single nucleotide polymorphisms (SNPs) have been widely used in the study of aquaculture genomics, genetics, and breeding research since they are the most prevalent molecular markers on the genome. Currently, a large number of SNP markers from cultured fish species are scattered in individual studies, making querying complicated and data reuse problematic. We compiled relevant SNP data from literature and public databases to create a fish SNP database, FishSNP (http://bioinfo.ihb.ac.cn/fishsnp), and also used a unified analysis pipeline to process raw data that the author of the literature did not perform SNP calling on to obtain SNPs with high reliability. This database presently contains 45,690,243 (45 million) nonredundant SNP data for 13 fish species, with 30,288,958 (30 million) of those being high-quality SNPs. The main function of FishSNP is to search, browse, annotate and download SNPs, which provide researchers various and comprehensive associated information.

Pigment matters: Behavior and lateralization of albino and pigmented fish (Bronze Corydoras) in aquaculture

Animal welfare science recognizes fish as sentient beings capable of experiencing pain, stress, and various emotions. As social interactions and mutual relationships are essential for fish welfare, the social environment in aquacultures is important for fish welfare. Pigmentation influences fish social behavior, e.g., communication and/or shoaling behavior. We investigated how pigmentation and shoal phenotypic composition affect locomotor activity in relation to feeding, exploratory behavior, sheltering and lateralization in holding tanks and Y-mazes in pigmented and albino Bronze Corydoras (Corydoras aeneus). The fish were divided into three treatment groups: pigm only, alb only, and mix groups. Each group comprised 12 shoals, with a total of 288 fish distributed across 36 shoals, each containing eight individuals. The study revealed behavioral differences between fish with pigmented and albino phenotypes, both within and among shoals. For both phenotypes, an increase in locomotor activity before feeding was followed by a decrease in activity after food consumption, indicating an anticipatory response and a shift from foraging to postfeeding behavior. In the mixed shoals, pigmented fish exhibited greater activity and sheltering behavior than albino fish. Both albino and pigmented fish showed lateralization toward the right arm of the Y-maze; however, in the mixed shoals, the preference for the right arm was not significant. Albino fish reached the shelter at the end of the Y-maze more often; however, in the mixed shoals, albino fish maintained their success rate in exploring the maze, while pigmented fish showed an increased success rate. We emphasize the significance of considering phenotypic variation and shoal composition when evaluating fish behavior and welfare. Such insights can inform the management of practices in aquaculture and ornamental breeding to ensure optimal fish welfare and enhance their overall quality of life.

Theoretical Analysis and Expression Profiling of 17β-Hydroxysteroid Dehydrogenase Genes in Gonadal Development and Steroidogenesis of Leopard Coral Grouper (Plectropomus leopardus).

The differentiation and developmental trajectory of fish gonads, significantly important for fish breeding, culture, and production, has long been a focal point in the fields of fish genetics and developmental biology. However, the mechanism of gonadal differentiation in leopard coral grouper (Plectropomus leopardus) remains unclear. This study investigates the 17β-Hydroxysteroid Dehydrogenase (Hsd17b) gene family in P. leopardus, with a focus on gene characterization, expression profiling, and functional analysis. The results reveal that the P. leopardus's Hsd17b gene family comprises 11 members, all belonging to the SDR superfamily. The amino acid similarity is only 12.96%, but conserved motifs, such as TGxxxGxG and S-Y-K, are present in these genes. Hsd17b12a and Hsd17b12b are unique homologs in fish, and chromosomal localization has confirmed that they are not derived from different transcripts of the same gene, but rather are two independent genes. The Hsd17b family genes, predominantly expressed in the liver, heart, gills, kidneys, and gonads, are involved in synthesizing or metabolizing sex steroid hormones and neurotransmitters, with their expression patterns during gonadal development categorized into three distinct categories. Notably, Hsd17b4 and Hsd17b12a were highly expressed in the testis and ovary, respectively, suggesting their involvement in the development of reproductive cells in these organs. Fluorescence in situ hybridization (FISH) further indicated specific expression sites for these genes, with Hsd17b4 primarily expressed in germ stem cells and Hsd17b12a in oocytes. This comprehensive study provides foundational insights into the role of the Hsd17b gene family in gonadal development and steroidogenesis in P. leopardus, contributing to the broader understanding of fish reproductive biology and aquaculture breeding.