Fish Aquaculture Research Articles

Identification of body coloration related genes in ricefield eel (Monopterus albus) using GWAS

Body color is one of the most diverse external morphological characteristics of fish. It not only affects the function of fish predation and individual communication but also has important economic value. The ricefield eel (Monopterus albus) is a popular freshwater aquaculture fish species in China. Few studies have suggested some candidate genes involved in the formation of body color in this fish; however, further genetic evidences are required. Genome-wide association analysis (GWAS) is a powerful analytical method for identifying relationships between target traits and genetic markers or candidate genes in natural populations. In this study, two populations of ricefield eel with different body coloration were used to study the genetic factors that regulate the formation of body color. Through GWAS, 67 SNPs, 463 genes and 5 signaling pathways were found to be associated with body color. These results suggest that a complex molecular regulatory mechanism regulates ricefield eel body coloration. Our findings lay the foundation for subsequent genome selection breeding of ricefield eel.

Accelerating microplastic contamination in 210Pb dated sediment cores from an urbanized coastal lagoon (NW Mexico) since the 1990s

The ubiquity of microplastics (MP) across all ecosystems raises concerns about their potential harm to the environment and living organisms. Sediments are a MP sink, reflecting long-term accumulation and historical anthropogenic impacts. Three 210Pb-dated sediment cores were used to understand the temporal variations of MP abundances (particles kg−1) and fluxes (particles m−2 year−1) within the past century in Estero de Urías Lagoon, an urbanized coastal lagoon in the Mexican Pacific. MP particles, extracted from sediments by density separation (saturated NaCl solution) were counted using a stereomicroscope, under visible and ultraviolet light on Nile red (NR) stained filters. The polymer composition was determined in ∼10 % of the suspected MP particles using Fourier Transform Infrared spectrometry. Fibers (66 to 89 % of the total particles) predominated over fragments (11 to 34 %). Before 1950, no MP particles were detected. Polyethylene terephthalate (PET) was the prevalent synthetic polymer (up to 50 % of the particles), while semisynthetic cellulosic fibers were predominant, underscoring the broader scope of anthropogenic contamination. Suspected MP abundances (NR stained filters) were highest in the core collected at the innermost area, which was attributed to the lagoon's hydrodynamics, since current velocities decrease from the proximal to the distal area to the sea. From the regression between MP fluxes and time elapsed since sediments deposited, the cores showed consistent accelerated increases of MP burial since mid-20th century, most likely because of the increasing availability of plastic products and population growth, with the consequent increment in plastic waste and wastewater releases. Our findings emphasize the growing MP pollution challenges at EUL, which may directly impact subsistence fishing and shrimp aquaculture activities, threatening local livelihoods and food sources; and also highlight the need for improved waste management and pollution control strategies in rapidly industrializing regions, to protect both aquatic ecosystems and human populations dependent on fishing products.

Effect of Synthetic Hormone on Breeding Potential of Gold Fish (Carassius auratus)

The acquisition of ornamental fish is becoming a prerequisite for luxury. Fish which are ornamental are getting progressively more popular as a way to alleviate stress. Among these, goldfish and koi carp are the most prevalent visually appealing fish that happen to be consistently in demand by fish hobbyists. For millennia, the method of raising these fish has been standardized. One of the most significant advancements in the aquaculture of ornamental fish that are vital to economic prosperity is artificial propagation. Induced breeding is a straightforward approach that guarantees a timely supply of seed spawn for fish culture. The aim of the current study was to use ovaprim™ hormone at various dosages to encourage breeding in gold fish (Carassius auratus auratus) kept in captivity. Every breeding pair, including the control, was bred. There were significant (<0.05) variations in the success of fertilization and hatching rate at various doses between treatments and the control group. Ovaprim™ at a dose of 0.7ml/kg and 1.4ml/Kg was found to be effective for male and female respectively with 54% fertilization rate, 43 % hatching rate. The positive response to synthetic hormone (ovaprim™) with considerable fertilization and hatching rate makes it possible to conduct the breeding program of this species commercially and the method can be applicable for commercial culture.

Effect of heat exposure on histology, transcriptomics and co-expression network: A synthetic study in Japanese flounder (Paralichthys olivaceus)

Water temperature has continued to increase as part of global warming. The heart of fish is the center that participates in the physiological limitations of thermal performance. However, only a few studies have focused on the response mechanisms of fish hearts to heat stress. Therefore, the economically important cold-water aquaculture fish, Japanese flounder (Paralichthys olivaceus) was chosen to explore the mechanisms of the heart in response to heat stress. Histological observations indicated that heat stress could widen the sarcoplasmic distance and deepen chromatin staining. Further transcriptome analysis identified 958 differentially expressed genes (DEGs), and significantly enriched “Protein processing in endoplasmic reticulum” pathway and related terms in functional enrichment analysis. Weighted gene co-expression network analysis (WGCNA) showed that different tissues had different response modules and hub genes, and calcium ions (Ca2+) related genes and pathways were noteworthy in the heart specific module. Functional identification of key Ca2+ regulatory hub genes illuminated that caveolin-3 (cav3) was an important gene that participates in controlling the Ca2+ into and out of cells. Meanwhile, overexpression of cav3 could reduce heat stress induced apoptosis. This study could not only be a crucial resource for the response mechanisms underlying heat stress in Japanese flounder, but also provide valuable insights into genetic improvement for heat-resistance.

Decoding the fish genome opens a new era in important trait research and molecular breeding in China.

Aquaculture represents the fastest-growing global food production sector, as it has become an essential component of the global food supply. China has the world's largest aquaculture industry in terms of production volume. However, the sustainable development of fish culture is hindered by several concerns, including germplasm degradation and disease outbreaks. The practice of genomic breeding, which relies heavily on genome information and genotypephenotype relationships, has significant potential for increasing the efficiency of aquaculture production. In 2014, the completion of the genome sequencing and annotation of the Chinese tongue sole signified the beginning of the fish genomics era in China. Since then, domestic researchers have made dramatic progress in functional genomic studies. To date, the genomes of more than 60 species of fish in China have been assembled and annotated. Based on these reference genomes, evolutionary, comparative, and functional genomic studies have revolutionized our understanding of a wide range of biologically and economically important traits of fishes, including growth and development, sex determination, disease resistance, metamorphosis, and pigmentation. Furthermore, genomic tools and breeding techniques such as SNP arrays, genomic selection, and genome editing have greatly accelerated genetic improvement through the incorporation of functional genomic information into breeding activities. This review aims to summarize the current status, advances, and perspectives of the genome resources, genomic study of important traits, and genomic breeding techniques of fish in China. The review will provide aquaculture researchers, fish breeders, and farmers with updated information concerning fish genomic research and breeding technology. The summary will help to promote the genetic improvement of production traits and thus will support the sustainable development of fish aquaculture.

A Review of the Benefits of the Sustainable Utilization of Shrimp Waste to Produce Novel Foods and the Impact on Human Health

In recent years, there has been an increase in the industrial processing of shrimp, aiming to cover the increasing demand for shrimp products for human consumption, and, consequently, an increase in shrimp by-products as shrimp waste. This waste includes the cephalothoraxes, heads, shells, tails, pleopods, and exoskeleton appendages of processed shrimps. The appropriate method for the enzymatic hydrolysis of shrimp waste can recover its bioactive substances, including carotenoids. Thus, these xanthophylls and carotenes are of high financial interest and have high antioxidant, anti-inflammatory, and anti-cancer activities. Therefore, these substances can be incorporated into fish feed as ingredients that improve fish health and simultaneously lead to the production of aquaculture fishes similar in coloration to the wild ones. Thus, the consumption of such novel food acts as a preventive factor for human health. In this regard, β-carotene has antioxidant and fat-soluble activities owing to vitamin A sufficiency and has an anti-cancer effect, too. Canthaxanthin can be used as a product for personal care and as a natural tanning agent for human skin. Zeaxanthin and lutein have positive effects on various eye and heart diseases, neuronal damage, human skin diseases, and certain types of cancer. Astaxanthin also has anti-diabetic and anti-obesity properties. Therefore, the purpose of this review is to highlight the sustainable utilization of shrimp waste via enzymatic hydrolysis, the benefits of a fish diet enriched with astaxanthin, the consumption of fish enriched with carotenoids, and the effects of carotenoids on human health. The problem of shrimp waste disposal affects the environment, does not contribute to sustainable development, and is directly related to the phenomenon of environmental change.

Life stage and vaccination shape the gut microbiome of hatchery-reared Atlantic salmon (Salmo salar) intended for river stocking

Microbiomes play an essential role in promoting host health and fitness in fishes, but the factors driving variation in gut microbiomes among individuals are not fully recognized. Understanding the biological and environmental factors influencing variation in the gut microbiome in fishes is needed to link microbiome composition to host physiology and potentially design manipulations to improve rearing success in fisheries and aquaculture. In this study, we characterized the gut microbiomes of Atlantic salmon (Salmo salar), a globally important species in commercial aquaculture and recreational fishing, considering life stage, vaccination status, and hatchery origin. Microbiomes diverged between hatchery sub-adults (age-0 parrs) and wild adults, with sub-adults exhibiting higher diversity and more similar microbiome communities when compared to adults. The diversity and composition of gut microbiomes did not differ between groups of adults that were reared in two different hatcheries and sampled from the wild. We also found that oral vaccines against bacterial kidney disease (BKD) reduced gut microbial diversity within individual sub-adult salmon, driving increased differentiation of gut microbial communities among individuals. Unvaccinated sub-adults displayed a stable core gut microbiome that was greatly reduced upon vaccination for BKD. Our results suggest that life stage is an essential factor shaping the gut microbiome of Atlantic salmon, likely driven by differences in habitat and diet, and that BKD vaccination can lead to a rapid disruption of the gut microbiome. Conditions experienced in the hatchery environment appear to have a strong influence on host gut microbiomes, but differences at early life stages may be lost due to environmental factors experienced in the wild. The plasticity of the gut microbiome throughout the life of individuals may have important implications for understanding host health, with potential applications for improving the rearing and reintroduction success of the ecologically and economically important Atlantic salmon.

Pichia pastoris composition expressed aerolysin mutant of Aeromonas veronii as an oral vaccine evaluated in zebrafish (Danio rerio)

Vaccines are one of the most practical means to stop the spreading of Aeromonas veronii in aquaculture. In this study, virulence factor aerolysin mutant NTaer which has lost its hemolytic activity was used as a target antigen. Pichia pastoris constitutive secretory expression NTaer (GS115-NTaer) was used as a potential safe oral vaccine to evaluate its effectiveness on zebrafish immunity. The result shows that vaccination of GS115- NTaer for four weeks did not affect the growth performance of the host, while eliciting an effective immune protective response. Compared with the control group, the GS115-NTaer could significantly up-regulate the relative expression level of the intestinal tight junction protein 1α (TJP1α) gene, and significantly increased the contents of lysozyme (LYZ), complement C3 and C4 in the gut, indicating that the innate immune response of the fish was activated. The relative gene expression levels of macrophage-expressed gene 1 (MPEG1) and T cell receptor (TCR-α) in the gut, and MPEG1, CD4, CD8, TCR-α, GATA3, and T-bet in the spleen were all increased significantly, indicating that the cellular immune response of the fish was activated. Furthermore, the contents of serum IgM and intestinal mucosa IgZ antibodies were significantly increased, which showed that humoral immunity was also activated. Moreover, inoculation with GS115-NTaer significantly changed the structure of gut microbiota. In particular, the relative ratio of (Firmicutes + Fusobacteriota + Bacteroidota)/Proteobacteria was significantly higher than that of the control and GS115 groups. Lastly, the vaccinated fish were challenged with A. veronii, and the relative percent survival of GS115 and the GS115-NTear groups was 14.28% and 33.43%. This improvement of immunity was not only due to the specific immune response but also attributed to the improvement of innate immunity and the gut microbiota which was demonstrated by the germ-free zebrafish model. Collectively, this study provides information on the effectiveness of GS115-NTear as an oral vaccine for the green prevention and control of A. veronii infection in fish aquaculture.

Sea urchin waste as a promising nutritional source for the polychaete Hediste diversicolor (OF Müller, 1776)

In aquaculture, species diversification emerges as an imperative sustainable strategy, essential for mitigating both biological and financial risks. In this context, the cultivation of sea urchins has gained prominence as an emerging trend. However, its commercial viability still faces several challenges, namely limited growth performance. Integrated multi-trophic aquaculture (IMTA) represents a potentially more profitable model by integrating extractive species to mitigate ecological impacts and promote circular economy principles. The use of polychaetes in IMTA has proven effective in recycling waste from fish aquaculture production, however, their potential should be further explored in low-trophic aquaculture solutions. This study evaluated the potential of reared sea urchin biodeposits as a nutritional feed source for the polychaete Hediste diversicolor (OF Müller, 1776). H. diversicolor juveniles were fed three diets, over 50 days: sea urchin waste (SUW), fish waste (FW) and fish feed (FF). Survival, growth, and protein and fatty acid (FA) contents were assessed. Total survival was observed in all treatments except for FW (98%). Polychaetes fed SUW and FF presented similar specific growth rates. The protein level in the polychaetes fed SUW was significantly lower, reflecting the diet's composition. The FA profile of H. diversicolor was also influenced by the respective diets. The absolute content (μg mg−1 DW) and FA profile of polychaetes were significantly different among treatments, reflecting the composition of the diets. Saturated FA (SFA) represented the dominant class in the polychaetes fed with waste diets, while in FF polychaetes polyunsaturated fatty acids (PUFA) were the major group. Nevertheless, polychaetes fed the waste diets demonstrated the PUFA biosynthetic capacity of this species, showing a considerably higher proportion of essential long-chain FA, compared to diets. Overall, these preliminary results suggest, for the first time, the potential for recycling sea urchin biodeposits into a polychaete biomass with high commercial value, presenting a promising opportunity for low-trophic integrated aquaculture models.

Effect of Pond-Based Rice Floating Bed on the Microbial Community Structure and Quality of Water in Pond of Mandarin Fish Fed Using Artificial Diet.

The culture of mandarin fish using artificial feed has been gaining increasing attention in China. Ensuring good water quality in the ponds is crucial for successful aquaculture. Recently, the trial of pond-based rice floating beds (PRFBs) in aquaculture ponds has shown promising results. This research assessed the impact of PRFBs on the microbial community structure and overall quality of the aquaculture pond, thereby enhancing our understanding of its functions. The results revealed that the PRFB group exhibited lower levels of NH4+-N, NO2--N, NO3--N, TN, TP, and Alk in pond water compared to the control group. The microbial diversity indices in the PRFB group showed a declining trend, while these indices were increasing in the control group. At the phylum level, there was a considerable increase in Proteobacteria abundance in the PRFB group throughout the culture period, suggesting that PRFBs may promote the proliferation of Proteobacteria. In the PRFB group, there was a remarkable decrease in bacterial populations related to carbon, nitrogen, and phosphorus metabolism, including genera Rhodobacter, Rhizorhapis, Dinghuibacter, Candidatus Aquiluna, and Chryseomicrobium as well as the CL500_29_marine_group. Overall, the research findings will provide a basis for the application of aquaculture of mandarin fish fed an artificial diet and rice floating beds.

Feed Components and Timing to Improve the Feed Conversion Ratio for Sustainable Aquaculture Using Starch.

Aquaculture contributes to the sustainable development of food security, marine resource conservation, and economy. Shifting aquaculture feed from fish meal and oil to terrestrial plant derivatives may result in cost savings. However, many carnivorous fish cannot be sustained on plant-derived materials, necessitating the need for the identification of important factors for farmed fish growth and the identification of whether components derived from terrestrial plants can be used in feed. Herein, we focused on the carnivorous fish leopard coral grouper (P. leopardus) to identify the essential growth factors and clarify their intake timing from feeds. Furthermore, we evaluated the functionality of starch, which are easily produced by terrestrial plants. Results reveal that carbohydrates, which are not considered essential for carnivorous fish, can be introduced as a major part of an artificial diet. The development of artificial feed using starch offers the possibility of increasing the growth of carnivorous fish in aquaculture.

Tracking Biomarkers for the Health and Welfare of Aquaculture Fish

Aquaculture production has been growing consistently over the last few decades to meet the increasing animal protein demand of the human population. However, increased production and rearing intensities raise the challenges of guaranteeing fish health and welfare, which is essential to avoid losses and ensure product quality. Biomarkers can provide insights into the fish’s nutritional, physiological, and health status, and aid in the evaluation of early nutritional and physiological imbalances, distress conditions, and pathological diagnosis. The discovery and validation of biomarkers rely mostly on the use of information provided by different parameters, including biochemical, metabolic, or immunologic, as well as several omics, from genomics and transcriptomics to proteomics and metabolomics. In this review, a summary of the main biomarkers used in aquaculture is provided along with an overview of the main omics technologies available for further biomarker research. This review also highlights the need to develop non-lethal biomarkers that can easily and quickly be measured to provide a prompt response to producers.

Hydrolysis Optimization of Thraustochytrid (Heterotrophic Protist) Biomass for the Production of a New and Sustainable Ingredient for the Aquafeed Industry

Thraustochytrids biomass, rich in docosahexaenoic acid (DHA), could be a sustainable ingredient for the aquafeed industry. However, its production cost renders it less competitive than fishmeal and fish oil from wild-caught fish. This study proposes optimizing the hydrolysis conditions of thraustochytrid biomass to generate an ingredient with improved properties thanks to the production of peptides with different biological activities. The improved nutritional value of the biomass could justify its use to decrease the amount of wild-caught fish in aquafeed, which would enhance the sustainability of fish aquaculture. First, two commercial proteases, Papain and Alcalase 2.4L, were compared for their capacity to hydrolyze the biomass. The best degree of hydrolysis (19 ± 1%) was obtained with Alcalase 2.4L, which was then used for the optimization of the pH, enzyme concentration and reaction time using response surface methodology. The results showed that the highest concentration of peptides and DHA in the aqueous phase was obtained with a pH, enzyme concentration and reaction time of 7.5, 2.7% and 205 min, respectively. If thraustochytrid hydrolysates prove to improve fish fitness, this mild and free-solvent process protocol could be used to produce a sustainable ingredient for aquafeed.

C-Jun N-terminal kinase 1/P53 signaling mediates intrinsic apoptosis of largemouth bass (Micropterus salmoides) hepatocytes under heat stress

The increasing frequency of high-temperature extremes threatens largemouth bass Micropterus salmoides, a significant fish for freshwater ecosystems and aquaculture. Our previous studies at the transcript level suggested that heat stress induces hepatic apoptosis in largemouth bass. In the current study, we sought to validate these findings and further investigate the role of the c-Jun N-terminal kinase (JNK)/P53 signaling in hepatic apoptosis under heat stress. First, heat treatments were conducted in vivo and in vitro under different temperatures: 28 °C, 32 °C, and 37 °C. In primary hepatocytes subjected to heat treatment, cell viability was evaluated via the Cell Counting Kit-8, while mitochondrial membrane potential and nuclear morphology were assessed through JC-1 and Hoechst 33258 staining, respectively. We observed reductions in both cell viability and mitochondrial membrane potential (ΔΨm), along with alterations in nuclear morphology, in primary hepatocytes exposed to heat stress at temperatures of 32 °C and 37 °C. Quantitative real-time PCR revealed significant alterations in the expression profiles of intrinsic apoptosis-related genes within liver tissues under heat stress. Immunohistochemistry analysis revealed that JNK1 signaling increased as the temperature increased, JNK2 expression increased only at 37 °C, and JNK3 expression did not change with temperature. We speculate that JNK1 and JNK2 have pro- and anti-apoptotic effects, respectively. Western blot analysis conducted on cultured hepatocytes further validated these findings. JNK inhibition reduced hepatocyte apoptosis, improved nuclear morphology, and maintained ΔΨm even after 37 °C treatment. These results not only confirm that heat stress led to intrinsic apoptosis of hepatocytes but also indicated that JNK1 could mediate P53 expression and activate caspase-dependent intrinsic apoptosis in largemouth bass hepatocytes under such conditions. This study illuminates the physiological responses of largemouth bass to acute heat stress, offering valuable insights into the potential impacts of climate change on freshwater fishes and the sustainability of aquaculture.

Research on Sea Trial Techniques for Motion Responses of HDPE Floating Rafts Used in Aquaculture

The innovative aquaculture equipment known as high-density polyethylene (HDPE) floating rafts has gained popularity among fishermen in the southeast coastal regions of China. Compared to deep-water anti-wave fish cages, the construction costs of HDPE floating rafts are 50% to 75% less. There is a dearth of comprehensive publicly available records of HDPE floating rafts sea trial data, despite substantial numerical studies on the motion response of aquaculture fish cages and scale model experiments under controlled-wave conditions. This study involves sea trial techniques under operational and extreme environmental conditions for motion responses of HDPE floating rafts, presents a comprehensive procedure for sea trials of HDPE floating rafts, summarizes the issues encountered during the trials, and suggests solutions. Using MATLAB for independent programming, motion videos and photos collected from the sea trials are processed for image capture, yielding the original time history curve of vertical displacement. Based on the sea trials’ data, including motion displacement, acceleration, mooring line force, overall deformation patterns, and current and wave data, recommendations are provided for the design and layout of HDPE floating rafts. Based on the Fast Fourier Transform (FFT) method for spectral analysis, the influence of interference items on the observational data is eliminated; the rationality of the observational data is verified in conjunction with the results of the Gabor Transform. This study offers a scientific analytical method for the structural design and safe operation of HDPE floating rafts and provides a reference for subsequent numerical simulations.

Navigating aquaculture losses: Tackling fish‐killing phytoflagellates in a changing global landscape

AbstractAquaculture has emerged as a pivotal alternative for seafood production, addressing the challenges posed by depleting wild fish stocks. However, the industry faces substantial challenges, notably the presence of harmful algal blooms (HABs), which can cause serious economic consequences. The proliferation of major species of phytoflagellates leading to massive fish mortality is on the rise, possibly attributed to increasing global temperatures and eutrophication. This underscores the critical need for robust detection, prevention, and mitigation strategies to safeguard the aquaculture industry. This contribution offers valuable insights into comprehending and addressing the challenges posed by HABs in the fish aquaculture sector in an era of global change.

More than just geosmin and 2‐methylisoborneol? Off‐flavours associated with recirculating aquaculture systems

AbstractThe consumption of seafood is driven by flavour, yet achieving its high quality remains a challenge for many species reared in recirculating aquaculture systems (RAS). A comprehensive knowledge of off‐odour sources in aquatic foods is indispensable in ensuring flavour quality standards. At the beginning of the production chain, early post‐harvest lipid oxidation products develop into endogenous off‐odours and accumulate over time. These malodours add to those already absorbed exogenously, namely from the water and feeds, although the information on the interactions between these sources is currently scarce. Despite geosmin and 2‐methylisoborneol receiving significant attention in relation to fish off‐flavour, only limited knowledge on the molecular and ecological mechanisms driving their production in aquatic environments has been reported. Moreover, RAS‐hosted bacteria have been associated with a wide range of other odour‐active compounds, such as pyrazines, terpenoids, and other degradation byproducts that are frequently overlooked when studying flavour taint in fish. The influence of aquaculture feeds on the flavour of fish flesh has been underestimated, too, both as a source of off‐odours but also as a novel modulator strategy to achieve desirable aquatic food flavours. Finally, the influence of water treatment processes widely used in RAS operations, such as advance oxidation process, ozone, ultraviolet and hydrogen peroxide disinfections, is greatly underexplored with respect to odour quality. This article reviews the current scientific evidence with supporting data on the chemical diversity of off‐odours found in aquaculture fish worldwide and their potential sources and highlights knowledge gaps that should be addressed in future research.

Effects of dietary tryptophan levels on growth performance, serotonin metabolism, brain 5-HT and cannibalism activities in tiger puffer, Takifugu rubripes fingerlings

Essential amino acid (EAA) requirements of aquaculture fish species can be used as a guideline for commercial feed formulation. Several EAA requirements have been quantified in tiger puffer (Takifugu rubripes). However, as the third limiting amino acid (AA) of many plant protein sources, tryptophan requirement of this species has yet to be quantified. This study was conducted to determine dietary tryptophan requirement of tiger puffer, and investigate the effect of dietary tryptophan supplementation on the cannibalism, brain serotonin (5-hydroxytryptpamine, 5-HT) metabolism and serum cortisol levels. Six experimental diets were prepared using fish meal, gelatin and corn protein concentrate as intact protein, and then supplemented with crystalline AA premix. The analyzed tryptophan levels in the experimental diets were 3.5, 4.1, 4.5, 5.5, 7.0 and 11.8 g/kg of dry diet. Experimental diets were randomly fed in triplicate to tiger puffer (initial average weight of 17.5 g) for 58 days. The weight gain (WG), feed conversion ratio (FCR) and protein efficiency ratio (PER) were significantly affected by dietary tryptophan, and the break points were observed at 5.07, 4.82 and 4.99 g/kg of dry diet, respectively. Compared to the basal diet, the cannibalism (the rate of bite mark appearance) was significantly lower and survival rate was significantly higher when fish were given diets containing 7.0 and 11.8 g/kg tryptophan. The concentrations of free tryptophan and phenylalanine in the brain exhibited a nonlinear increase in response to the incremental levels of dietary tryptophan. Brain 5-HT concentration was significantly affected by dietary tryptophan levels, but did not show a significant dose-dependent response. The expression of genes related to 5-HT metabolism (tph1a, ddc and aldh) and serotonin reuptake (sert) in the brain varied significantly and exhibited a nonlinear relationship with the graded levels of dietary tryptophan. In addition, serum cortisol levels showed a decreasing trend till the 5.5 g/kg tryptophan inclusion level, at which point there appeared to be the lowest level. In conclusion, based on nonlinear regression analysis of the WG, FCR and PER, dietary tryptophan requirement of tiger puffer was determined to be range between 4.82 and 5.07 g/kg of dry diet (10.48–11.03 g/kg of dietary protein). Dietary tryptophan supplementation above requirement could mitigate cannibalism and improve the survival of tiger puffer, which may be attributed to regulating the synthesis and catabolism of 5-HT and its availability in the synaptic cleft, and subsequently the reduction of serum cortisol content.

The effect of an organomineral chelate complex on the amylolytic activity of intestinal enzymes of some fish species

To date, there is a large amount of information regarding the effect of heavy metals on the hydrolases of the digestive tract. It has been established that even biogenic metals in high concentrations can have a toxic effect. The assessment of the activity of digestive hydrolases is relevant, since a change in their activity has a direct effect on the effectiveness of assimilation of food. Amylolytic hydrolases help to provide the body with carbohydrates (along with fats) – the main sources of energy for fish. A decrease in the intake of carbohydrates will lead to a violation of metabolic processes and, as a result, underdevelopment and death of fish. The aim of the study was to determine the effect of an organomineral chelate complex on the amylolytic activity of intestinal enzymes of some fish species. The research was conducted at the Department of Biochemistry and Physiology of the St. Petersburg State University of Veterinary Medicine and on the basis of two fisheries in the Leningrad Region. The fish of the experimental groups (n = 10) were given an additive for 30 days, the data were compared with the control (n = 10). The drug was given together with the feed once a day, at a concentration of 0.5 g / kg (feed weight). Fingerlings (0+) of 3 species of freshwater bony fish were used as research objects: Carassius auratus (n=20), Cyprinus carpio (n=20), Oncorhynchus mykiss (n=20). Amylolytic activity was determined in the total homogenets of the intestinal mucosa of fish. The activity was assessed by the increase in hexoses by the Nelson method in the modification of Ugolev, Jesuitova. The detection was carried out on a photoelectric KKK-3 photometer. Based on the studies obtained, it can be concluded that the use of an organomineral chelate complex in the studied dosage (previously worked out in conditions of determining acute and chronic toxicity for fish) does not have a negative effect on the amylolytic activity of intestinal enzymes. There was no significant decrease in amylolytic activity in all experimental groups. Based on this, it is possible to recommend the use of a chelate complex for fish in industrial aquaculture.

Sterilization of fish through adaptable gRNAs targeting dnd1 using CRISPR-Cas13d system

Sterilizing fish is a valuable technique not only for preventing genetic contamination from escaped aquaculture fish but also for enhancing fish meat quality. The clustered regularly interspaced short palindromic repeats-CRISPR-associated 13d (CRISPR-Cas13d) system is capable of RNA-targeted gene knockdown with reduced off-target effects. Unlike morpholino knockdown, which is limited to specific target sites, the CRISPR-Cas13d system utilizes the entire mRNA as a target site for gRNA. This enables the design of adaptable gRNAs by targeting the conserved sequences across fish species, leading to promising sterilization for a wide variety of aquaculture fish. In this study, we demonstrated that the effectiveness of this system in fish sterilization by the knockdown of dead end1 (dnd1) and nanos3, which are crucial for germ cell development. Initially, we demonstrated that gRNAs designed using the cas13design tool, which was developed based on studies of cultured mammalian cells, effectively induced germ cell-deficient medaka with low-cytotoxicity. Additionally, we identified the nucleotide positions of the gRNA (seed sequence) that are crucial for knockdown in teleost fish. These data will be valuable for designing adaptable gRNA in teleost fish and targeting multiple paralogous genes. To develop an adaptable sterilization technique using the CRISPR-Cas13d system, we aligned 81 dnd1 sequences from 70 fish species and identified a highly conserved region of the gRNA targets. Despite not finding a perfectly matched target region in the dnd1 alignment, we designed 15 adaptable gRNAs that potentially targeting dnd1 in 55 out of 70 fish species, leveraging sequences from representative aquaculture and aquarium fish (salmon, tilapia, puffer fish, amberjack, tuna, guppy and carp) and experimental model fish (medaka, zebrafish, and stickleback. To confirm whether adaptable gRNAs had a knockdown effect, we initially injected the gRNAs into medaka embryos. Adaptable gRNAs with a single-nucleotide mismatch against medaka dnd1 resulted in the complete loss of germ cells with little cytotoxicity, suggesting that mismatches are unlikely to induce off-target effects crucial for embryonic development. Additionally, adaptable gRNAs designed based on the salmon dnd1 sequence, which was 100% identical in the Oncorhynchus, Salvelinus, and Salmo groups, effectively generated germ cell-deficient rainbow trout. These results indicate that the knockdown of dnd1 using the CRISPR-Cas13d system is effective for sterilizing both aquaculture and experimental model fish species. Moreover, the adaptable gRNAs designed in this study can potentially sterilize a diverse range of fish species.