Fishes, Volume 7, Issue 6 (December 2022) – 99 articles

The Chinese giant salamander (Andrias davidianus) is the biggest extant and endangered amphibian, which has an incongruous sex ratio during the artificial breeding process and is sex indistinguishable in appearance. The sex development mechanism of this rare species thus needs to be explored. We therefore conducted this study to explore the molecular mechanisms of sex hallmarks or gonad maintenance genes for CGS. In this study, we sequenced and analyzed the sexually mature male and female gonads of Chinese giant salamanders (CGSs) using RNA-seq technology and found a total of 15,063 differentially expressed genes (DEGs) in the testicular and ovarian tissues, of which 7973 (52.93%) were expressed in testicular and 7090 (47.07%) in ovarian tissues. Thirteen gonad DEGs were selected based on gene expression abundance and quantified in the muscle and skin tissues of both male and female CGSs. The results showed that these 13 DEGS, out of the 20 analyzed DEGs, were expressed in both the muscle and skin tissues and only two of them (Bmp15 and ZP3) were consistent in the muscle and skin compared to the gonads of CGSs of the two sexes. Overall, our study should provide an important reference for the sex-characteristics-related genes in this type of species, shedding new light on future research on this topic. Full article

Vaccines prepared from formalin-killed Streptococcus agalactiae were administered to Nile tilapia (Oreochromis niloticus) via three different routes: immersion in a water-based vaccine, injection with an oil-based vaccine, and as a water-based oral vaccine. All vaccination treatments increased lysozyme and peroxidase activity in skin mucus of Nile tilapia by 1.2- to 1.5-fold compared to their activities in unvaccinated control fish. Likewise, alternative complement, phagocytosis, and respiratory burst activities in the blood serum of the vaccinated fish were 1.2- to 1.5-times higher than in the unvaccinated fish. In addition, the expression transcripts of interleukin-1 (IL-1), interleukin-8 (IL-8), and lipopolysaccharide-binding protein (LBP) were 2.3- to 2.9-fold higher in the vaccinated fish compared to those in the unvaccinated control. The unvaccinated fish challenged with Streptococcus agalactiae had a survival rate of 25% compared to a survival rate of 78–85% for the vaccinated fish. The differences between the unvaccinated and vaccinated fish were all statistically significant, but there was no significant difference in any of the indicators of immunity between the three vaccinated groups. Collectively, these results confirm that vaccination with formalin-killed Streptococcus agalactiae significantly improved the resistance of Nile tilapia to infection by the pathogen. Overall, the efficacy of oral administration of the vaccine was comparable to that of vaccine administered via injection, indicating that oral vaccination is a viable cost-effective alternative to administering vaccines by injection. Full article

The aim of this study is to investigate the effect of 10 and 20% replacement of fishmeal (FM dietary group) with the superworm Zophobas morio larvae meal (ZM10 and ZM20 dietary groups) on the growth performance of sea bass (Dicentrarchus labrax) and lettuce plants (Lactuca sativa) reared in aquaponics. Ninety juvenile sea bass with an average body weight of 21.55 g/individual were placed in aquaponic fish tanks, together with 24 lettuce plants with an average initial height of 8.90 cm/plant and an average number of leaves of 5.75/plant over a 45-day trial period. At the end of that period, all feeding groups exhibited high survival. In fact, ΖΜ10 and ZM20 groups showed similar fish weight gain and specific growth rate (SGR) (p > 0.05), but significantly lower SGR (p < 0.05) than the FM group. Nevertheless, final fish body weight and length were similar (p > 0.05) for all feeding groups. No plant mortality was observed during the 45-day study period. All three aquaponic systems resulted in similar leaf fresh weight, as well as fresh and dry aerial biomass. At the end of the experimental period, plants in the third system showed higher fresh leaf weight, total weight of fresh leaves, total dry aerial biomass, and total produced biomass compared to the other two systems. The results of the present study show that fish fed with the ZM10 diet had higher weight gain (WG) than fish fed with the ZM20 diet, while the SGRs for ZM10 and ZM20 were similar. Both ZM10 and ZM20 diets result in efficient lettuce production. This study also provides data that enlighten the feasibility of integrating insect meals as fish feeds for aquaponics which helps towards the development of an ento-aquaponic approach. Full article

Ivory shell (Babylonia areolata) is a commercially important aquaculture species mainly found on the southeast coast of China. However, it has been greatly affected by vibriosis in recent years. In this study, FP17 (a potential pathogen) was isolated from a dying ivory shell with “acute death syndrome” and confirmed as a pathogen via infectious experiment. Furthermore, phylogenetic analysis based on the average nucleotide identity (ANI) sequencing of the 16S rRNA gene and housekeeping genes (ftsz, gapA, gyrB, mreB, pyrH, rpoA, and topA) indicated that FP17 was identical to Vibrio tubiashii. Transmission electron microscopy showed that FP17 is curved and has a short rod shape, with a single flagellum. Besides, the calculated LD₅₀ after the intramuscular injection of FP17 was 2.11 × 10⁶ CFU/g at 14 d. The genome of the FP17 strain consists of two chromosomes and one plasmid with 5,261,336 bp and 45.08% GC content, including 4824 open reading frames (ORFs) and 150 non-coding RNAs (ncRNA). Genome mining revealed that 120 candidate gene clusters, including vibrioferrin and flagellum-related proteins, are responsible for virulence. Comparative genomic analysis showed that vibrioferrin genes, such as pvs and type Ⅵ secretion system protein genes (vas), are specific in V. tubiashii FP17 but not in the ATCC19109 strain. Furthermore, 92 antimicrobial resistance (AMR) genes, such as tufA, tet(35), crp, etc., were mapped within the genome as the potential candidate for virulence, consistent with antibiotic susceptibility assay. This is the first study to describe the complete genome sequence of V. tubiashii infecting ivory shell. The genetic characteristics, virulence factors, and antimicrobial resistance of the V. tubiashii strain FP17 were also explored. Full article

Most of world’s fish and seafood are produced by aquaculture, which is one of the biggest contributors to the world’s food security. The substantial increase in prices of conventional feed ingredients and the over-exploitation of natural resources are some of the biggest constraints to aquaculture production. To overcome this stress, different approaches and techniques are used, among which the use of non-conventional feed ingredients in the aquaculture sector is the most recent approach. Different non-conventional feed ingredients such as plant-based products, algae (both micro and macroalgae), single-cell protein (bacteria and yeast), and insect meal are currently used in aquaculture for sustainable food production. Amongst all these novel ingredients, insects have greater potential to replace fishmeal. The existence of about 1.3 billion tons of food and agriculture waste from the food chain supply poses a serious environmental threat. Insects are tiny creatures that can thrive on organic waste and thus can convert the waste to wealth by the bioconversion and nutritional upcycling of organic waste. Insects have the potential to recover nutrients from waste aquaculture products, and many fish species feed on insects naturally. Therefore, employing insects in the aquaculture sector to replace fishmeal is an eco-friendly approach. The present review briefly highlights emerging non-conventional feed ingredients, with special attention given to insects. The current review also focuses on the nutritional value of insects, factors affecting the nutritional value of insects, potential insects that can be employed in the aquaculture sector, the physiological response of fish when fed with insect meal, techno-functional properties of insect meal, and emerging approaches for addressing possible downsides of employing insect meal in fish diets. Finally, it suggests avenues for further research into these inventive fishmeal replacements. Full article

Herein, we isolated the pathogenic strain ZZ051 from hemorrhagic channel catfish (Ictalurus punctatus). Physiological and biochemical identification, 16S rRNA gene sequence analysis, and MALDI-TOF-MS showed that the ZZ051 strain was Aeromonas veronii. After artificial infection, the diseased fish showed symptoms similar to the natural disease, and the characteristics of the bacteria reisolated from the tissues were the same as those of the original infection, indicating that the isolated strain ZZ051 was the pathogen responsible for the channel catfish disease. The ZZ051 isolate was highly sensitive to enrofloxacin but resistant to florfenicol. This study provided a theoretical basis for preventing and controlling hemorrhagic disease in channel catfish. Full article

Investigation of the use of fish scales as a medium for non-lethal biomonitoring has recently commenced. Fish scales have been shown to incorporate cortisol over longer periods of time than blood and thus provide a promising means of assessing long-term stress in many species of teleost fish. However, while cortisol is a major mediator of the stress response in fishes, downstream effects of chronic stress on reproduction can involve gonadal steroids such as progesterone and testosterone. The quantification of these additional hormones alongside cortisol could therefore allow for the assessment of both stress and consequential reproductive alterations. To investigate these concepts, we artificially elevated circulating cortisol, progesterone, and testosterone in rainbow trout (Oncorhynchus mykiss) using coconut oil implants for three weeks. Following this we quantified these three hormones as well as 11-ketotestosterone, a potent androgen in teleost fishes. In all cases serum samples reflected a significant increase in the injected hormone confirming the efficacy of this method; however, this did not result in significantly elevated scale concentrations of the same hormone in all cases. As the stress and reproductive axes are closely integrated, these findings are likely a result of interactions along the steroidogenic pathway indicating that a further investigation of the relationship between scale concentrations of these hormones and actual physiological processes is required. Nevertheless, the successful quantification of both stress and gonadal steroid hormones within the scale suggests that such measurements could provide a novel and informative tool in the assessment of long-term stress and the resulting effects on reproductive endocrinology in teleost fishes. Full article

The Sox family plays essential roles as transcription factors in vertebrates; however, little is known about the Sox family in Lutraria sieboldii. L. sieboldii are pleasant to eat with a short growth cycle and have become one of the best bottom-seeded enrichment species in Guang Xi. In this study, Sox2 (named LsSox2) and Sox9 (named LsSox9) from L. sieboldii were cloned, and their expression patterns were analyzed. The length of the LsSox2 gene coding sequence was 1011 bp, encoding 336 amino acids, and LsSox9 was 1449 bp, encoding 482 amino acids. LsSox2 had its highest expression levels in the ovary, which were 356 times those in testis, whereas LsSox9 presented higher expression in testis, which was 6 times more highly expressed than in the ovary. LsSox2 exhibited the highest expression during the morula stage, which was 20 times that of the D-shaped larvae or zygote. LsSox9 exhibited two expression peaks, one at the four-cell stage and the other at the trochophore stage, while the lowest expression was in the zygote. LsSox9 was 73 times more highly expressed in the four-cell stage than in the zygote stage. During gonadal development, LsSox2 presented the highest expression in the mature ovary, which was 756 times more highly expressed than in mature testis. LsSox9 presented higher expression in testis at the emission stage which was 6 times more highly expressed than in the ovary. These results indicate that LsSox2 and LsSox9 may play important roles in embryonic and gonadal development. Full article

The marine environment is the material basis for the survival and development of fishery resources, and changes in the marine environment affect the fishery economy. Therefore, against the background of sustainability and environmental uncertainty, it is important to investigate the development of the marine environment and the marine fishery economy to improve the quality of both. Taking the panel data for 11 coastal cities in China from 2011 to 2020, we use several methods, including the entropy method, a coupling harmonious degree model, and a Tobit model, to measure the marine-environment quality and marine-fishery-economy quality, their coordination, and the factors affecting that coordination. We find that (1) the marine-environment quality and marine-fishery economy quality show a significant upward trend over time, but they are spatially unbalanced, with obvious interprovincial differences. (2) Coordination between the marine-environment quality and marine-fishery-economy quality has risen steadily, but the level of coordination is still low, remaining at the primary level in most areas. (3) The important factors affecting coordination between the marine-environment quality and marine-fishery-economy quality include the strength of the marine fishery industry, scale of the marine fishery economy, production capacity of marine fisheries, marine-environment quality, and quality of the marine environment and its resources. In light of these findings, we should increase the coordination between the marine-environment quality and marine-fishery-economy quality by upgrading the marine fishery industry, modernizing marine fisheries, linking the environmental governance of marine and land areas, and strengthening the ecological construction of the marine environment. Full article

The development of specific diets for the juvenile stage is a main target for culture intensification of tench (Tinca tinca). Aquafeeds still rely heavily on the use of fishmeal (FM) but concerns about economic and ecological sustainability make the use of alternative protein sources necessary. Insect meals are considered a promising substitute to replace FM. In a 90-day experiment, 6 diets with different replacement levels of FM by partially defatted black soldier fly larvae meal (BSFLM): 0%, 15%, 30%, 45%, 60% and 75%, were tested on juvenile tench. Survival rates were high (95.8–100%) without differences between treatments. Diet with 45% FM replacement allowed for best growth performance in terms of total length (TL = 66.4 mm) and weight (W = 4.19 g), without differences with 60% and 75% of replacement. A cubic relationship was evidenced between the level of FM replacement and growth. From the regression equations, the estimated optimal level of FM replacement was 47% (356 g BSFLM kg⁻¹ diet). Externally visible deformities were always under 0.05%. The whole-body lipid content of the fish had a significantly negative linear regression with BSFLM (r² = 0.80). The content of the essential amino acids (EAA) arginine, leucine, lysine, phenylalanine, methionine, and threonine in diets decreased with dietary BSFLM inclusion. However, it did not have a negative effect on growth performance, suggesting that EAA requirements were covered. The amount of essential amino acids in whole-body juveniles was similar independently of the diet provided. The results allow considering BSFLM as a sustainable protein source for juvenile tench feeding. Full article

The issue of high-seas fisheries is the main threat to biodiversity in areas beyond national jurisdiction. The BBNJ Agreement, which focuses on biodiversity in areas beyond national jurisdiction, is under vigorous discussion. Subject to the “not undermine” requirement and considerations of practical interests, it is highly possible that the BBNJ Agreement may not address the issue of fisheries on the high seas. The objective of this paper is to analyze the relationship between the high-seas fisheries issue and the BBNJ Agreement for the purposes of the conservation of marine biodiversity, the unity of the marine ecosystem, and the consistency of regulations. It maintains that from the perspective of protecting the oceans, enacting legislation in areas beyond national jurisdiction, and transforming marine management mode, the issue of high-seas fisheries should be included in the BBNJ Agreement. In the future, the BBNJ agreement needs to clarify its scope of application, resolve overlapping issues through general regulations and conflict rules, clarify the methods and contents of international cooperation, and establish international law obligations for integrated ocean management. Full article

The Antarctic continent is one of the most pristine environments on planet Earth, yet one of the most fragile and susceptible to the effects of the ongoing climate change. The overwhelming majority of the components of Antarctic marine trophic chain are stenotherm organisms, highly adapted to the extreme, but extremely stable, freezing temperatures of the Antarctic ocean, which have not changed significantly during the past fifteen million years. Notothenioid fishes are the most abundant representatives of ichthyofauna at these latitudes, being ubiquitously found in coastal areas across the entire continent. While different Antarctic fish species have been previously subjected to studies aimed at defining their range of thermal tolerance, or at studying the response to acute thermal stress, just a handful of authors have investigated the effects of the exposure to a moderate increase of temperature, falling within the expected forecasts for the next few decades in some areas of the Antarctica. Here, the emerald rockcod Trematomus bernacchii was used as a model species to investigate the effects of a 20-day long exposure to a +1.5 ${}^{°}$C increase in the brain, gills and skeletal muscle, using a RNA-sequencing approach. In parallel, the experimental design also allowed for assessing the impact of stabling (including acclimation, the handling of fishes and their confinement in tanks during the experimental phase) on gene expression profiling. The results of this study clearly identified the brain as the most susceptible tissue to heat stress, with evidence of a time-dependent response dominated by an alteration of immune response, protein synthesis and folding, and energy metabolism-related genes. While the gills displayed smaller but still significant alterations, the skeletal muscle was completely unaffected by the experimental conditions. The stabling conditions also had an important impact on gene expression profiles in the brain, suggesting the presence of significant alterations of the fish nervous system, possibly due to the confinement to tanks with limited water volume and of the restricted possibility of movement. Besides providing novel insights in the molecular mechanisms underlying thermal stress in notothenioids, these findings suggest that more attention should be dedicated to an improved design of the experiments carried out on Antarctic organism, due to their extreme susceptibility to the slightest environmental alterations. Full article

Probiotics as antibiotic alternatives for preventing and controlling infectious diseases are a relatively eco-friendly strategy in aquaculture. The bacteriocin-producing probiotic Paenibacillus ehimensis NPUST1 was isolated from tilapia culture pond water in our previous study. The present study demonstrated that P. ehimensis NPUST1 produced hydrolytic enzymes, including protease, amylase, cellulase, xylanase and lipase. The effects of P. ehimensis NPUST1 on zebrafish nutrient metabolism, growth performance and innate immunity were evaluated by measuring the expression of indicator genes in zebrafish after feeding P. ehimensis NPUST1 at doses of 10⁶ and 10⁷ CFU/g for 8 weeks. There was an obvious increase in the hepatic mRNA expression of carbohydrate metabolism-related genes, including glucokinase, hexokinase 1, glucose-6-phosphatase, and pyruvate kinase, and growth-related genes, including the growth hormone receptor and insulin-like growth factor-1. The expression of the innate immune-related genes including interleukin (IL)-1β, IL-6, IL-15, tumor necrosis factor-α, toll-like receptor (TLR)-1, TLR-4, complement component C3b and lysozyme were significantly increased in P. ehimensis NPUST1-supplemented fish. A significant reduction in cumulative mortality was exhibited in P. ehimensis NPUST1-supplemented fish after infection with Aeromonas hydrophila and Streptococcus iniae. In conclusion, our data suggested that P. ehimensis NPUST1 supplementation in feed could potentially improve nutrient metabolism and growth in addition to enhancing innate immunity and disease resistance against A. hydrophila and S. iniae in zebrafish. Full article

Fish vaccination plays a vital role in the prevention of fish diseases. Inappropriate injection positions will cause a low immunization rate and even death. Currently, traditional visual algorithms have poor robustness and low accuracy due to the specificity of the placement of turbot fins in the application of automatic vaccination machines. To address this problem, we propose a new method for estimating the injection position of the turbot based on semantic segmentation. Many semantic segmentation networks were used to extract the background, fish body, pectoral fin, and caudal fin. In the subsequent step, the segmentations obtained from the best network were used for calculating body length (BL) and body width (BW). These parameters were employed for estimating the injection position. The proposed Atten-Deeplabv3+ achieved the best segmentation results for intersection over union (IoU) on the test set, with 99.3, 96.5, 85.8, and 91.7 percent for background, fish body, pectoral fin, and caudal fin, respectively. On this basis, the estimation error of the injection position was 0.2 mm–4.4 mm, which is almost within the allowable injection area. In conclusion, the devised method was able to correctly differentiate the fish body from the background and fins, meaning that the extracted area could be successfully used for the estimation of injection position. Full article

The black pomfret (Parastromateus niger) is one of the high-income-generating carangid fish species and the only known member of its genus. This study aims to identify existing gaps in stock status and population demography of this species and provide viable management recommendations to enhance the sustainability of this fishery. Therefore, three methodological approaches have been used in this study; TropFishR to present the current exploitation status, the length-based spawning potential ratio (LB-SPR) to quantify stock spawning biomass, and Froese’s sustainability indicators (LBI) to establish a basic standard for sustainable management of the fishery. In the length-weight relationship of black pomfret, an allometric growth pattern (b = 2.19) was found. The VBGF life history parameters for black pomfret were L_∞ = 55.25 cm, K = 0.54 year⁻¹, and based on LCCC analysis, the total mortality (Z = 1.61 year⁻¹), natural mortality (M = 0.69 year⁻¹) and fishing mortality (F = 0.91 year⁻¹) are calculated. The result reveals that this fishery is currently suffering from overexploitation and the stock’s spawning biomass (SPR = 13%) is below the limit reference point because most of the catch (82%) was found to be under the maturity level. Based on the results, this study recommended strictly maintaining the mesh size of the net to ensure not to catch immature fish with a length smaller than 30.63 cm, recommended the length to catch be between 29 and 35 cm, and reducing fishing pressure by one-third to ensure the sustainability of the black pomfret fishery. Full article

The Wallacean shortfall refers to the knowledge gap in biodiversity distributions. There is still limited knowledge for freshwater fish species despite the importance of focusing conservation efforts towards this group due to their alarming extinction risk and the increasing human pressure on freshwater ecosystems. Here, we addressed the Wallacean shortfall for freshwater fish faunas across Europe by using the completeness indicator derived from species accumulation curves to quantify the fish sampling efforts. The multiple potential drivers of completeness that were previously related to the sampling efforts for other species (i.e., population density, nature reserves, or distance to cities) were tested using a 10 × 10 km² grid resolution, as well as environmental (e.g., climatic) factors. Our results suggested that although there was an overall spatial pattern at the European level, the completeness was highly country-dependent. Accessibility parameters explained the sampling efforts, as for other taxa. Likewise, climate factors were related to survey completeness, possibly pointing to the river conditions required for fish sampling. The survey effort map we provide can be used to optimize future sampling, aiming at filling the data gaps in undersampled regions like the eastern European countries, as well as to account for the current bias in any ecological modeling using such data, with important implications for conservation and management. Full article

The removal of the net enclosure has been used as a lake management strategy in various regions of China as ecological development is given more attention. Nevertheless, little is known about the substantive impact of this measure on fish communities in inland lakes. To this end, the fish community composition and structural features after the removal of the net enclosure in Gehu Lake were explored and evaluated in this study from 2021 to 2022 and compared to the investigation before the net enclosure removal from 2017 to 2018. Belonging to 7 orders, 10 families, and 46 species, a total of 17,151 fish were collected, with pelagic, sedentary, and omnivorous species dominating. In comparison, the number of species increased by 10 after removal, and fish alpha diversity increased. The Index of Relative Importance (IRI) revealed that the composition of dominating species remained constant, including Coilia nasus, Hypophthalmichthys molitrix, and Hypophthalmichthys nobilis; Parabramis pekinensis, Megalobrama amblycephal, and Culter mongolicus were upgraded from common species to general species. Culter alburnus, Hemiculter bleekeri, and Pseudobrama simoni were downgraded from general species to common species. Elopichthys bambusa had become a common species (IRI = 109.35), which was not discovered before removal. According to the hierarchical clustering (HC) and non-metric multidimensional sequencing (NMDS), the fish community of the northern reserve was highly aggregated. As the Abundance Biomass Comparison (ABC) curve and biodiversity index indicated, the fish community structure of the whole lake was in a state of moderate anthropogenic disturbance with reduced stability, while that of the northern reserve was in a state of light anthropogenic disturbance with greater stability. The number of fish species increased in this survey compared to the period before removal, species and dominant species composition altered dramatically, and total lake stability declined. This study demonstrates that the fish diversity in Gehu Lake increased after the removal of the net enclosure. Meanwhile, the stability of the fish community structure was decreased temporarily. Lake restoration is a long-term process, and the underlying impact of the removal of the net enclosure still requires continuous monitoring and further studies. Full article

The boom-and-bust trajectory of the Argopecten purpuratus industry in Chile shows the progression from resource extraction (fishing) to production (aquaculture). This paper analyses the effects of environmental, economic, and scientific–technological factors. The influence of each factor on scallop production in Chile was reviewed for the period between the 1980s and 2020. The evaluation of the effects allows the visualisation of the industry’s productive evolution and reveals the current challenges. The occurrence of abrupt environmental disturbances, commercialisation under imperfect market configurations, and public and private efforts in scientific and technological advances have acted favourably on scallop production. However, an industry mainly focused on prices and high production volumes did not devote much effort to develop low-cost climate-resilient technologies. Today, economic challenges must be addressed by helping to reduce production costs and add economic value to products and by-products. Our results show that the industry must focus on low-cost technologies, the use of renewable energy, and the circularity of its processes. The environment ensures the capture of natural seeds and their adaptation to climate change. These challenges must not lose sight of the emerging effects of the COVID-19 pandemic. Full article

The present study aimed to evaluate the feasibility of a formulated diet to replace live baits as feed for Siniperca chuatsi. A 2 × 2 factorial design with three replicates was used to investigate the effects of conventional live baits (LB) and a formulated diet (FD) on the growth, muscle nutrition composition, and digestive enzyme activities of S. chuatsi at two growth stages. The results showed that the feed conversion ratio (FCR) in the FD group was significantly lower than that in the LB group. The final body weight (FBW) and weight gain (WG) were not significantly different between the two feeding modes. However, at the juvenile stage, the specific growth rate (SGR) in the FD group was significantly lower than that in the LB group. Muscle moisture, crude protein, and crude lipid contents were not influenced by dietary treatments. There were no significant differences in ∑EAA, ∑NEAA, and ∑AA compositions of the juvenile and adult stages fed the two kinds of diets. At the juvenile stage, histidine (His) content in the FD group was significantly higher than that in the LB group; at the adult stage, cysteine (Cys) content in the FD group was significantly higher than that in the LB group; at both growth stages, Met content in the FD group was significantly lower than that in the LB group. The FD group showed higher levels of ∑SFA, ∑HUFA, ∑n-3PUFA, n-3/n-6, EPA, and DHA than the LB group did, whilst the opposite occurred in the MUFA levels. In addition, fish fed with LB had significantly higher values of pepsin and intestinal trypsin activities in the juvenile fish compared to the FD group, but the activities were not significantly different between the two feeding modes at the adult stage. The activities of stomach and intestine amylase in the FD group were significantly higher than those in the LB group. Overall, these results showed that under long-term feeding conditions, S. chuatsi fed with the artificial diet had no significant difference in muscle crude protein, crude lipid, amino acid composition, and digestive capacity, but showed superiority in the composition of fatty acids such as EPA and DHA levels compared to the live baits group. Therefore, the artificially formulated diet might be a more appropriate feeding approach for sustainable development of the S. chuatsi industry. Full article

This experiment aimed to study the effects on liver tissue structure and immune performance of grass carp Ctenopharyngodon idellus when the common reed Phragmites australis is in its diet, instead of wheat Triticum aestivum L. Seventy-two healthy grass carps (145.52 ± 2.56 g) were randomly divided into three groups according to their body weight. Fishes in each group were fed an essential diet with 0% (control group), 50% and 100% (test group) common reed, instead of wheat, respectively. After feeding for 41 days, the changes of serum biochemical indices, liver tissue structure and immune related indices of grass carp were detected. The results showed that, compared with the control group, the activities of serum alanine transaminase (ALT) and aspartate transaminase (AST) in the substitution groups were significantly increased (p < 0.05), but still at a normal level. The contents of total protein, albumin and globulin did not change significantly (p > 0.05). Compared with the control group, the liver cells of grass carp in the substitution groups had clear boundaries, tight arrangement and less vacuolation. The contents of serum interleukin-1 (IL-1) and complement 3 (C3) in the 100% substitution group were significantly higher than those in the control group (p < 0.05), and the contents of liver IL-1 and total complement (CH50) in the 100% substitution group were significantly higher than those in the control group (p < 0.05). The contents of IL-1, C3 in serum and IL-1, CH50 in liver in the 50% substitution group were significantly higher than those in the control group (p < 0.05). The mRNA relative expression levels of C3, IL-1, MHC-I and interferon (IFN) in the head-kidney, kidney, liver and spleen of grass carp were significantly affected by feeding the grass carp with different common reed substitution ratios (p < 0.05). In summary, common reed, instead of wheat, in feed can improve the liver tissue structure, and increase the non-specific immune response level, of grass carp. Full article

Kidney-type glutaminase, encoded by the gls1 gene, plays a critical role in glutamate production and improvement of meat flavor. In this study, a gls1 gene encoding 595 amino acids was cloned from triploid crucian carp (Carassius auratus) (TCC) and showed a high similarity with the gls1 gene found in Cyprinus carpio, Sinocyclocheilus rhinocerous and Puntigrus tetrazona. Comparing the abundance of gls1 in different tissues, we found its expression level in the brain and liver were significantly higher than that in heart, gut, kidney, spleen and muscle. gls1 expression in the brain reached the highest value. In addition, the expression levels of gls1 also appeared different in diurnal variation, with the highest expression seen at 9:00, while it was low at 3:00, 6:00, 15:00 and 24:00. Furthermore, dietary regulation of gls1 expression was investigated in our study. In each feeding trial, each diet was randomly assigned to triplicate tanks. Fish were fed one of the tested diets up to satiation twice daily. The results showed that gls1 expression increased in 32% protein group and decreased in 35–41% protein group. The results of different protein source experiments showed that the expression of gls1 gene in the mixed protein group (the control group) was significantly higher than that in the fish meal and soybean meal groups. Glutamate treatment revealed that appropriate concentrations (0.10 mg/mL in vivo and 2.00% in vitro) of glutamate remarkably improved the expression of gls1. Besides, diets supplemented with 0.80–1.60% lysine-glutamate dipeptide exhibited a down regulatory impact on gls1 expression. In conclusion, this study demonstrated that the expression of gls1 in TCC was increased by 32% protein diet, mixed protein source diet and diet with 2.00% glutamate concentration, while decreased by 0.80–1.60% lysine-glutamate dipeptide. The findings of this study provide a reference for the regulation of gls1 and have a potential application in the optimization of dietary formula in aquaculture. Full article

Global warming implies the risk of a changing oxygen regime in the seas and oceans of our planet. The mitochondrial complex of nuclear erythrocytes of cartilaginous fish, as the energy basis of blood cells, has repeatedly encountered such climatic fluctuations throughout their evolutionary history. In this regard, the features of the adaptive strategy of the erythrocyte mitochondrial complex in the thornback ray (Raja clavata L.) are of interest from the evolutionary and ecological points of view. The rate of oxygen consumption in resuspended (Ht = 25–30%) erythrocytes taken from the Black Sea thornback ray in saline was studied by the polarographic method. A high “basal” rate of respiration in the erythrocytes of the thornback ray was shown, which ranged from 10.5 to 21.6 pmol O₂ min⁻¹·10⁶ cells. The addition of substrates of the mitochondrial respiration activators glutamate, maleate, and succinate to the erythrocyte suspension caused a 2–6-fold increase in the respiratory activity of thornback ray erythrocytes. In cases where the rate of respiration of erythrocytes was high, protonophore–dinitrophenol caused an inhibition of the activity of mitochondrial respiration. At low respiration rates of erythrocytes, its effect was opposite and caused a stimulation of mitochondrial respiration. Oligomycin caused a significant inhibition of the respiratory activity of the red blood cell suspension of the thornback ray. This suppression of cell respiration was enhanced under conditions of exposure to the permeabilization of erythrocytes with digitonin. This can be recommended as one of the ways to block the respiratory activity of erythrocytes in cartilaginous fish. Another way of effectively blocking the respiration of the mitochondrial complex of the thornback ray’s erythrocytes was the effect of the blockers rotenone and sodium azide. The peculiarity of the mitochondria of the erythrocytes of the thornback ray was the absence of the complete inhibition of respiration by sodium azide (NaN₃), which is characteristic of the mitochondria of other fish species. Our data on the activation of the “respiration” of erythrocytes in fish indicate that the potential capabilities of cold-blooded and warm-blooded vertebrates have rather similar characteristics. This may indicate the initial “laying” of the architecture of the inner membrane to support the energy potential of the mitochondria of the cell. Full article

Fish larvae suffer high starvation mortality during the transition from yolk absorption to exogenous feeding, and the size of the developing buccal structures limits the food they can consume. Determining the suitable timing and size of live or inert foods could decrease this mortality. We described mouth development and determined the yolk absorption rate and point-of-no-return (PNR) of Dormitator latifrons larvae. One male and one female specimen were induced to spawn using salmon GnRHa implants, and 45 of their larvae were sedated and observed under a microscope every 24 h to measure total length, standard length, yolk sac length, yolk sac width, oil globule length, oil globule width, width of the oesophagus, and length of the upper and lower jaw longitudinal. The growth model, maximum mouth opening, daily survival, and starvation period were determined. The larval growth was fastest during the first 24 h post−hatching (HPH) at 28 ± 1 °C with an average increase of 625.42 µm in total length and 573.51 µm in standard length. The highest percentage of yolk absorption (52%) occurred within 24 HPH and at 96 HPH the yolk sac was completely reabsorbed. The PNR was reached at 156.41 HPH (p < 0.05). At 96 HPH, the upper and lower jaw were distinguishable by mouth movements. Our results suggest that the larvae of D. latifrons should be fed at 96 HPH with prey measuring 50–65 µm. Full article

It is necessary to determine the optimal temperature for Percocypris pingi growth in recirculating aquaculture systems. To describe the effects of temperature, we evaluated the growth, antioxidant enzyme activity, and gut microbiota structure of P. pingi at different temperatures, including 14, 18, 22, and 26 °C. Results showed that increases in body weight of individuals of the groups subjected to 18 and 22 °C temperatures were considerably higher than those in the groups subjected to temperatures of 14 and 26 °C between 20 and 60 d after the experiment started. Acid phosphatase activity in the liver and kidneys of P. pingi did not differ significantly among the various temperature groups (p > 0.05). A gradual restoration of the alkaline phosphatase and superoxide dismutase activities to variations in the surrounding temperature was observed in the liver and kidney of P. pingi. Interestingly, the water temperature did not affect the α-diversity or composition of the gut microbiota of P. pingi. In conclusion, water temperatures between 14 and 26 °C significantly impacted the growth of P. pingi (p < 0.05) but not the liver and kidney antioxidant capacity or the gut microbiota within 60 d. Full article

In recent years, global warming of anthropogenic origin and its impacts on biodiversity have increasingly gained public awareness. Here, we demonstrate that embryonic temperature can have persistent and crucial effects on zebrafish swimming capacity and cardiac shape. Three different embryonic temperature treatments (T_E = 24, 28 or 32 °C) were applied to zebrafish embryos until hatching. Fish were then raised in common conditions (28 °C) until adulthood. Ventricle roundness was found to increase significantly with a rise in T_E in juvenile (10% increase) and male (8% increase), but not female fish. T_E and sex significantly affected zebrafish swimming performance. Juveniles, males and females raised in cold (24 °C) presented significantly greater swimming capacity than those raised at 28 and 32 °C T_E. Our results represent a direct link between the physical capacity of adult fish and embryonic temperature fluctuations that add to the emerging rationale of the potential climate change scenarios on wild fish populations. Full article

Heat shock proteins (HSPs) are molecular chaperone proteins that can help maintain cellular protein homeostasis, assist in correcting the folding of cellular proteins, and protect organisms from stress when the body is under stress conditions such as temperature changes or bacterial infections. In this study, the HSP10 and HSP40 genes of Eriocheir hepuensis were cloned and named Eh-HSP10 and Eh-HSP40. The results show that the coding sequence length of the HSP10 and HSP40 genes of E. hepuensis was 309 bp and 1191 bp, encoding 102 and 396 amino acids, respectively. The results of protein domain prediction show that Eh-HSP10 has a Cpn10 domain. The Eh-HSP40 protein contains a DnaJ domain, which is characteristic of the HSP40 gene family. The results of qRT-PCR show that the Eh-HSP10 and Eh-HSP40 genes were expressed in different normal tissues, with the highest expression in the heart. Under Vibrio parahaemolyticus stress, the Eh-HSP10 genes peaked at 6 h, and the Eh-HSP40 peaked at 9 h in the hepatopancreas. In the gill, Eh-HSP10 showed a double peak at 24 and 48 h, and the expression of Eh-HSP40 was time-dependent. In the heart, the expression of Eh-HSP10 increased first and then decreased, whereas Eh-HSP40 peaked at 48 h. The results indicate that the Eh-HSP10 and Eh-HSP40 proteins may play a role in protecting E. hepuensis under V. parahaemolyticus infection and that they may be involved in the innate immune response of E. hepuensis against bacteria. Full article

Strontium marking technology is commonly used for extensive marking in stock enhancement and releasing activities. In order to explore the feasibility of this technology for juvenile Takifugu obscurus, five different concentrations of strontium (0, 12, 18, 36, and 72 mg/L) were set up by strontium chloride hexahydrate (SrCl₂·6H₂O) and T. obscurus were immersed for 7 days. Then, T. obscurus were reared in non-additive water for 25 days. The results showed that the survival rate of all groups was 100%, except the 72 mg/L group, after 7 days of immersion. Moreover, the growths of all the marked groups were better than that of the control group. There was no significant difference between the control and marked groups, except for the 18 mg/L group, indicating that the appropriate concentration of strontium might have positive effect for T. obscurus. The strontium to calcium (Sr/Ca) ratios of otoliths in the marked groups increased with increasing concentration and time, which were higher than the baseline, respectively. Then, the Sr/Ca ratios returned to the original level, but the peak value was still retained, suggesting that the success rate of the strontium marking reached 100%. Notably, the residual strontium content of 18 mg/L group was insufficient for causing negative effects for T. obscurus after 25 days. Therefore, in consideration of the growth, survival, and effect of strontium marking on otolith, 18 mg/L is an appropriate concentration for strontium marking of juvenile T. obscurus. This study confirmed the feasibility of strontium marking for T. obscurus and provided a new approach to rationally and scientifically evaluate the stock enhancement and releasing efficiency of T. obscurus. Full article

Koi herpesvirus (KHV) is a highly contagious virus that causes high mortality in koi and common carp, leading to a reduction in production worldwide. Recent diagnostic tests based on molecular methods alone (nucleic acid amplification) and indirect immunoassay methods (antibody detection) can be confirmed over KHV infections or prior exposure and latent infections. Unfortunately, there is no established method to detect KHV virus particles, especially when virus titers are low. Therefore, we propose an alternative, direct immunoassay method for viral detection using a single-chain variable fragment (scFv), a specific region of IgG antibodies that binds specifically to KHV particles. The results of functional analyses indicated that four putative scFv candidates, C5, F8, F6, and E4, were specific to KHV, but only F6 and C5 had a high binding affinity. The binding characteristics were confirmed by indirect competitive and sandwich enzyme-linked immunosorbent assays, which indicated that F6 and C5 have a broad penetration area to the binding region and share a similar epitope with commercial KHV monoclonal antibodies. These characteristics were further confirmed by their interactions with purified KHV coat protein by indirect ELISA and Western blot analyses. In conclusion, the F6 and C5 scFvs have adequate binding affinity to KHV particles to permit their use in immunoassays. Full article