Fishes, Volume 7, Issue 4 (August 2022) – 70 articles

Streptococcus agalactiae is an important bacterial pathogen in intensive Nile tilapia production, causing high mortality rates and great economic losses. This work aimed to evaluate the Nile tilapia vaccination against S. agalactiae and fed with ration containing probiotic AQUA PHOTO^® composed of Bacillus subtilis and Lactobacillus plantarum, on the immune response action and gut microbiota. The experimental design was completely randomized with five treatments (CON = control; ADJ = adjuvant; PRO = probiotic; VAC = vaccine; PRO + VAC = probiotic + vaccine) and five replicates. The vaccine (bacterin + adjuvant) was injected after 21 days (21d) of probiotic feeding and the vaccine was booster 14 days post-vaccination (35d). After 14 days of the booster (49d), the fish were challenged with S. agalactiae and observed for more than 14 days, completing 63 days. The immunized group showed a better survival rate (CON 40%; ADJ 57%; PRO 67%; VAC 87%; PRO + VAC 97%). The treatments VAC and PRO + VAC, after booster produced higher levels of IgM antibodies compared with the control from the same time. The combination of probiotic and vaccination provided better protection against S. agalactiae infection, directly affecting the gut microbiological profile. These results indicated the contribution of probiotic to the adaptive immune response through the modulation of the intestinal microbiota, improving the effect of the vaccination. In conclusion, AQUA PHOTO^®, composed of B. subtilis and L. plantarum, orally administered to Nile tilapia vaccinated against and challenged with S. agalactiae increases protection from infection and modifies the intestinal microbiota profile of the host, promoting the microbiota balance and improving adaptive immune response. Full article

Serranus scriba is a common member of the coastal fish community in the Adriatic Sea, but knowledge about its feeding ecology is scarce. The aim of this paper is to present new evidence about its food preferences and feeding habits. An innovative non-destructive method of fecal pellet analysis was used for this study. This method does not require sacrificing specimens and the fish can be released back into the sea alive after the laboratory work. The results demonstrated that S. scriba mainly preys on decapods, followed by polychaetes, isopods, fish, mollusks and swarming shrimps. The calculated index of trophic diversity (ITD) value of 0.89 indicates that it is an opportunistic feeder that feeds on a wide range of different prey. According to the calculated trophic level of 3.43, which is higher than that of other members of the community, S. scriba is also an important piscivorous predator. With age, S. scriba undergoes an ontogenetic shift. The proportion of crustaceans, gastropods and polychaetes decreases with age and body size, while the proportion of fish increases. Full article

This study aimed to characterize the intestinal microbiota of wild thick-lipped grey mullets (Chelon labrosus) and explore its potential functionality on the host. Intestinal contents of anterior and posterior sections from wild fish were collected and DNA was extracted. Subsequently, the V3–V4 regions of 16S rRNA were sequenced using the Illumina technology and results were analyzed by bioinformatics pipeline. The functional profile of the microbial community was analyzed using PICRUSt software. Shannon and Simpson diversity indices were significantly higher in the posterior section of wild specimens. The overall taxonomic composition suggests a certain homogeneity in the anterior section of the intestine and heterogeneity in the posterior section. Due to this, no statistical differences were detected at any level among both intestinal sections. Predicted functions of intestinal microbiota showed the most abundant were those related to amino acid metabolism, carbohydrate metabolism, energy metabolism, membrane transport, and cell replication and repair. Furthermore, the analysis revealed microbial functional genes related to the elimination of environmental toxins. Full article

Daily growth patterns and their relationship with reproduction was analyzed in the European hake from the Galician Shelf, where it shows a very protracted spawning with three spawning peaks. The daily growth analysis was performed in otoliths of adult females on the transversal section of the sagittae otolith. Daily increments were measured from the border to the nucleus in females until they were discernible. Results show that daily growth of females decreases during the spawning period because they allocate less energy to somatic growth in favor of the production of gametes, with an increase in growth in July. Lastly, daily growth individual trends showed a “spawning pattern” in 28% of medium and large females, suggesting an individual spawning period of one to two months, with 4–5 valleys of narrow daily increments, likely associated to batch release: individual spawning frequency would be 4–5 days. This is the first time that individual spawning frequency in hake is estimated based on individual data. Finally, the spawning pattern is detected only once per year, indicating that a single female participates only in one spawning peak per year, supporting the hypothesis of the existence of two or more spawning components in the stock. Full article

The assertive growth of photovoltaics (PV) will occupy a lot of land resources. There is also a needed land resource to expand the culturing area of Eriocheir sinensis. The aquavoltaic systems offer a potential solution to integrate PV power and E. sinensis culturing. In this study, we cultured E. sinensis in an area of PV panels (PV group) and an area with no PV panels (control group), respectively. The results showed that the weight gain rate, body length, body width, and meat yield of male crabs in the PV group significantly increases. In addition, the moisture of muscles, hepatopancreas, and testes in the PV group has significantly increased, and the total lipids of the hepatopancreas and muscles in the PV group were significantly decreased. Moreover, the PV panels affected the content of eight amino acids in different tissues, including Met, Arg, Cys, Pro, Gly, Leu, Tyr, and His. In addition, several saturated fatty acids (SFA), monounsaturated fatty acids (MUFA), and polyunsaturated fatty acids (PUFA) had been significantly influenced by the PV panels. ∑MUFA, docosahexaenoic acid (DHA), ∑n-3 PUFA, ∑n-6 PUFA, and n-3/n-6 PUFA ratio (p < 0.05) in the PV group had significantly decreased. The results of tissue color showed that the L* value of ovaries was significantly higher than in the control group, and a* and b* values of hepatopancreas were significantly lower. In conclusion, PV panels could promote growth performance and amino acid nutrition of crabs. However, the PV panels had a few negative influences on the fatty acid composition and tissue color. Full article

The effects of various levels of alkalinity stress (0, 18.25, 35.41, 52.53 and 69.74 mmol/L) in Chinese mitten crab (Eriocheir sinensis) were investigated by means of measuring hepatopancreas antioxidant system and serum nonspecific immune system-related indices at 0, 12, 24, 48 and 96 h, hepatopancreas tissue structure at 96 h. The activities of superoxide dismutase (SOD), catalase (CAT), glutathione (GSH) and aspartate aminotransferase (AST) in each concentration group generally showed a trend of a first increasing and then decreasing during the 96-h stress process (p < 0.05), while no significant changes were observed in the blank group during this period (p > 0.05). The activities of CAT, GSH and AST in all treatment reached peak values at 24–48 h. At 96 h of alkalinity stress, the activities of GSH, alanine aminotransferase (ALT), acid phosphatise (ACP) and alkaline phosphatise (AKP) in the 18.25 mmol/L group were not significantly different with the control group (p > 0.05). The activities of SOD and CAT in the 52.53 and 69.74 mmol/L treatment were significantly lower than those in the control group (p < 0.05), and the level of total antioxidant capacity(T-AOC), ALT, ACP and AKP in the 69.74 mmol/L group were significantly higher than those in the other groups (p < 0.05). Hepatopancreatic histological observation showed that the hepatopancreas of E. sinensis in the control group was normal. With increasing alkalinity, the basal membrane of the hepatopancreas fell off or even ruptured. Additionally, the number of hepatopancreas vacuoles increased, the volume of B cells and their internal transport vesicles increased, epithelial cells disintegrated, and the nucleus gradually shrank. E. sinensis can activate antioxidant and nonspecific immune systems to adapt to alkalinity stress. However, oxidative stress, immune system damage and hepatopancreas structure damage were caused when the stress exceeded the adaptive capacity of the body. Full article

Globally, over 85% of oyster reefs have been lost, and the combined effects of climate change, ocean acidification, and environmental degradation, including pollution and mangrove overharvesting, could further reduce global oyster fisheries in the coming decades. To understand the level of impact of climate change on the oyster fishery in West Africa, an expert-based vulnerability assessment to climate change was conducted for the West African mangrove oyster (Crassostrea tulipa, Lamarck 1819). Using a combination of the exposure of the oyster to climatic stressors (estuarine temperature, salinity, river flow, surface run-off, sea level rise, and estuarine circulation) together with an assessment of sensitivity to these stressors, we estimate the overall vulnerability of C. tulipa to climate change. A very high overall climate vulnerability score of 12 on a scale of 16 was calculated for C. tulipa. While the overall climate exposure score in the West African coastal region remained high, the high sensitivity of C. tulipa to hydrographic conditions of its habitat, in particular salinity, coupled with its sessile and habitat-specific nature, pushed the overall vulnerability to very high. Early life history settlement requirements, adult mobility, and sensitivity to salinity were the three most important biological and sensitivity attributes that determined the vulnerability score. By leaving each of these three sensitivity attributes out of the analysis, the overall vulnerability score was reduced to 9 (i.e., from very high to high). A negative directional effect of climate change, coupled with a low potential for change in distribution, threatens the C. tulipa fishery in a long-term adverse climate scenario. We recommend management efforts that incorporate climate resilience and adaptation practices to prioritize recruitment success, as well as the development of breeding lines with climate-resilient traits. Full article

Engraulis ringens (E. ringens) is a small pelagic fish of which the geographic and bathymetric distribution is conditioned by fluctuations in oceanographic conditions at different time scales (daily, weekly, monthly, annually, supra-annually, and longer) and by fishing. Understanding the organism−environment interactions and predicting the spatial distribution of its schools can improve conservation actions and fishery management, along with the operation of the fleets targeting E. ringens. There is an important fishery of E. ringens in Northern Chile (18°21′ S–26°00′ S), which provides about 80% of the purse seine catch. To identify and predict potential fishing grounds for E. ringens in this system, we implemented a predictive model of fishing grounds based on neural networks, which was trained with the georeferenced data of daily catches by industrial purse sein ships from 2003 to 2020 and information on oceanographic variables (sea surface temperature, salinity, depth of the mixed layer, sea height, and currents) obtained from the Copernicus Marine Enviroment Monitoring Service (CMEMS program). The neural network model had a very good performance (86%). Longitude (23%) was the most relevant variable for identifying potential fishing grounds, followed by the mixed layer depth (18%), latitude (15%), sea surface temperature (12%), month (12%), sea height (9%), salinity (9%), and the zonal and meridional components of the current velocity (2%). The neural network model classified correctly the majority of the areas with and without fishing potential; thus, its use is recommended to predict fishing grounds for E. ringens in the study area. Its application could increase by 88% of the probability of capture anchovy by the purse seine fleet of Northern Chile. Full article

As growth-promoting feed additives, compound acidifiers (CAs) have been widely reported in many farmed fish species, whereas there is little information on the application of CAs in the eel diet. The present trial was conducted to evaluate the supplementation effects of CAs on growth performance, serum biochemical parameters, and body composition of the juvenile American eel (Anguilla rostrata). The CAs supplementation levels in the diet of American eel were 0, 2.0, 3.0, 4.0, and 5.0 g/kg, respectively. The trial lasted for 12 weeks. The most beneficial effects of CAs on promoting growth performance, decreasing levels of serum lipid, modifying parameters of the liver function and immune function in the serum, and increasing the utilization of calcium and phosphorus in the diet were observed in the fish fed with 4.0 g/kg CAs. Dietary CAs supplementation had no significant effects on the body composition of whole fish, whereas 5.0 g/kg of dietary CAs supplementation exerted negative effects on growth performance, serum biochemical parameters, and utilization of calcium and phosphorus. The recommended level of CAs in the diet was 3.5–3.7 g/kg to achieve the optimal weight gain and feed conversion ratio for the juvenile American eel. Full article

The present study investigates the effects of dietary protein levels on glucolipid metabolism, immune function, and resistance to Streptococcus agalactiae of genetically improved farmed tilapia (GIFT) exposed to high temperature. Six practical diets were prepared to feed 360 fish (initial weight 43.78 ± 0.12 g) with graded protein levels (26.45%, 29.28%, 31.69%, 33.68%, 36.18%, and 38.75% dry matter). The results showed that 26.45% dietary protein significantly improved glycolysis by increasing PK mRNA levels, while the 29.28% and 31.69% dietary protein levels promoted gluconeogenesis by increasing PEPCK and G6Pase mRNA levels. For lipid metabolism, 26.45% dietary protein enhanced lipid synthesis by increasing PPAR-γ, SREBP1c, and FAS mRNA levels, while 31.69% dietary protein enhanced the level of lipolysis by increasing the PPAR-α and CPT1 mRNA levels. The highest plasma TG and TC contents were observed in the 29.28% and 31.69% dietary protein groups, respectively. In terms of antioxidants and immunity, the 31.69% dietary protein level activated the expression levels of HSP90 mRNA, thus increasing the expression levels of antioxidant-related genes (CAT, SOD, and GPx), and upregulating the anti-inflammatory factor IL-10 mRNA levels. In addition, regarding the antioxidant enzymes, the highest GSH content was found in the 29.28% dietary protein group, while the 31.69% dietary protein group had the maximum GSH-Px activity. The lowest plasma ALT and AST activities were observed in the 31.69% dietary protein group. Ultimately, the survival rate of juvenile GIFT fed 31.69% dietary protein was highest after a Streptococcus agalactiae challenge. Overall, 29.28–31.69% dietary protein was recommended in the diet of GIFT in a high-temperature environment. Full article

Scientific methods are used to monitor fish growth and behavior and reduce the loss caused by stress and other circumstances. Conventional techniques are time-consuming, labor-intensive, and prone to accidents. Deep learning (DL) technology is rapidly gaining popularity in various fields, including aquaculture. Moving towards smart fish farming necessitates the precise and accurate identification of fish biodiversity. Observing fish behavior in real time is imperative to make better feeding decisions. The proposed study consists of an efficient end-to-end convolutional neural network (CNN) classifying fish behavior into the normal and starvation categories. The performance of the CNN is evaluated by varying the number of fully connected (FC) layers with or without applying max-pooling operation. The accuracy of the detection algorithm is increased by 10% by incorporating three FC layers and max pooling operation. The results demonstrated that the shallow architecture of the CNN model, which employs a max-pooling function with more FC layers, exhibits promising performance and achieves 98% accuracy. The presented system is a novel step in laying the foundation for an automated behavior identification system in modern fish farming. Full article

Cimei Island is a second-class outlying island. In recent years, due to the lack of coastal fishery resources and restrictions on traffic and climate, the traditional fishery and tourism industries that residents rely on for a living have faced challenges. This research is based on the Barbados Programme of Action, from the perspective of environmental conservation, industrial economy, and social development in sustainable development, and from the perspective of local stakeholders, to construct a sustainable tourism action approach and development mechanism in Cimei Island. A qualitative research method was adopted. Various sources of data, including focus discussions and in-depth interviews with local stakeholders, textual materials, and field observations, were collected and analyzed. The results are as follows: (1) Cimei faces great threats in social, economic, and environmental aspects, which has led to Cimei Islands’ promotion of permanent development. (2) The current development of Cimei cannot effectively drive industrial development or the transformation of fishing villages. However, residents are worried that overdevelopment will impact the ecological environment and lifestyle on the Islands. (3) Cimei’s sustainable tourism development approach should be to first take inventory of the ecological environment and cultural resources, plan related environmental laws and regulations, and finally, use sustainable tourism to drive industrial development to carry out island development. Full article

Accurate checklists of species are essential for evaluating their conservation status and for understanding more about their distribution, biology and ecology and, therefore, the first step in order to effectively protect them. According to the existing literature, the Greek seas are rich in chondrichthyan biodiversity and herein, we update the most recent chondrichthyan checklist for the country regarding the species that are present in the Greek waters, correct unvalidated miscellaneous sightings and observations and provide guidelines about future research to improve their conservation. In total, 330 sources were collected from which 276 were used for further analysis, resulting in 1485 records of 67 species, among which 61 are confirmed by experts, including 34 sharks, 26 batoids and one chimaera. We are further listing six species as “Questionable/Not Confirmed”. Full article

Changes in the physiological and behavioral states of fish are affected by foreign substances. Therefore, fish need a certain adaptation period to eliminate the stress response. Herein, in order to determine the adaptation period, the bionic robot fish was used to obtain behavioral information about crucian carp, which was tested at five time points (1st, 7th, 14th, 21st and 28th day) within 28 days. First, the fear response and exploratory behavior of crucian carp affected by three-color bionic robot fish were explored. Then, according to the measurement results of the behavior, morphology, and feeding, and the physiological and biochemical properties of the crucian carp, a multi-parameter evaluation method was proposed to determine the adaptation period of the crucian carp under this monitoring mode. The results showed that more than 4 areas were occupied by crucian carp from the 21st day. From the 16th day, the number of crucian carp swimming with clear outlines gradually increased. The number of abnormal swimming occurrences decreased on day 13. More than 80% of the crucian carp body color returned to dark on the 23rd day. The crucian carp did not respond to food until day 19, when most of the crucian carp began to scramble for food. Food consumption reached more than two thirds on day 22. In addition, glucose and total protein leveled off after day 21, when mean hemoglobin levels were highest. Triglycerides showed a trend of first decreasing and then increasing. The pigmented area of the skin section gradually decreases and eventually stabilizes. In summary, it takes at least 23 days for the crucian carp to adapt to the influence of the bionic robot fish. Full article

Zebrafish (Danio rerio) are becoming one of the most important model organisms in behavioural neuroscience. It has been shown repeatedly that different zebrafish strains show large behavioural differences. These divergent behavioural profiles may have a genetic basis, but environmental factors and previous experience are also known to greatly affect the behavioural phenotype of zebrafish. It could be expected that behavioural differences at the larval stage should be less affected by environmental factors and experience. In the present study, we screened larvae of zebrafish of the AB strain and offspring of wild-caught zebrafish for boldness, using an open field test. In order to follow the behavioural development, we studied larvae at the age of 5-, 7-, 12- and 30-days post fertilization (dpf). Behaviour, as well as behavioural development, clearly differed between the larvae of the different strains. Wild larvae showed larger total distance moved than AB larvae, both at light and dark conditions. These differences were already present at 12 dpf but became more pronounced with age. Wild larvae had a greater variance compared to AB larvae for most of the variables. We have previously shown that bold and shy adult zebrafish differ in the brain expression of dopamine and opioid receptors. The results of the current study show that wild larvae display significantly higher brain expression of drd2b than AB larvae at 30 dpf, a difference that could be related to differences in activity. We did not detect any differences in the expression of opioid receptors. Full article

Glutamine synthetase (GS) is a key enzyme that catalyzes the synthesis of glutamine from glutamate, which plays a role in the promotion of muscle cell growth and in improving the flavor of meats. In this study, a GS gene encoding 371 amino acids was cloned from triploid crucian carp and showed the highest level of similarity with the GS gene found in Cyprinus carpio. Meanwhile, GS was differentially expressed in different tissues, and its day–night expression changes showed obvious oscillation. Additionally, the effects of glutamate and glutamine on GS expression in muscle cells were investigated in vitro and in vivo. We found that its expression was obviously increased due to high levels of glutamate (2 mg/mL) but decreased by glutamine in vitro. However, it was significantly promoted by glutamate and glutamine in vivo, with an optimal concentration of 2%. Furthermore, the use of lysine–glutamate dipeptides as feed additives also had a positive influence on GS expression (the optimal concentration is 0.8%). Finally, we explored the effects of different protein levels and sources on the expression of GS, and the results demonstrated that GS had the highest expression at the 35% protein level, but no significant differences were observed in the different protein sources between the fish meal diet (FM) and the mixed diet comprising soybean meal and rapeseed meal (SM). This study sheds new light on the regulation of GS in teleost fish and provides new perceptions and strategies for the formulation of high-quality feed for triploid crucian carp. Full article

The population of the Chinese white dolphin along Taiwan’s west coast is under a range of threats. The designation of marine protected areas (MPA) is urgently required for their protection. However, conflicts between specific species conservation and fishing rights mean that the success of such a designation relies on the fishers’ perceptions and awareness of an MPA. Designating offshore wind farms within MPAs can be a mechanism for minimizing conflicts between fisheries and conservation. The purpose of this study is to examine the potential for designating an offshore wind farm within an MPA for Chinese white dolphin conservation by exploring the attitudes of local fishers. This study used face-to-face questionnaires. The results show that the main challenges are conflicts of interest, insufficient science-based information, and inadequate law enforcement. Offshore wind farms could be a way to maximize the benefits for different stakeholders and positively impact the marine environment and ecosystem. This study makes feasible recommendations on how to improve conservation, promote renewable energy, and encourage sustainable fisheries. Full article

Climate change is a growing threat to marine organisms and ecosystems, and it is already modifying ocean properties by, for example, increasing temperature and decreasing pH. Increasing water temperature may also lead to an impairment of primary productivity and an overall depletion of available zooplankton. Understanding how the crossover between warming and zooplankton availability impacts fish populations has paramount implications for conservation and mitigation strategies. Through a cross factorial design to test the effects of ocean temperature and food availability in a temperate marine teleost, Pomatochistus flavescens, we showed that hindered feeding impacted sheltering and avoidance behaviour. Also, low food availability impaired fish reproduction, particularly male reproduction, as the expression of cyp11b1, a gene with a pivotal role in the synthesis of the most important fish androgen, 11-ketotestosterone, was significantly reduced under a low food regime. In contrast, temperature alone did not affect reproductive success, but offspring showed increased saturated fatty acid content (embryos) and increased lipid peroxidation (larvae). Altogether, food availability had a stronger effect on fitness, showing that coping with elevated temperatures, an ability that may be expected in shallow-water fish, can be indirectly impacted, or even overwhelmed, by the effects of ocean warming on primary productivity and downstream ecological processes. Full article

Fish population fluctuations have been widely documented and are often attributed to climate variability, but little is known about their relationship. This is a barrier that restricts our capacity to understand climate effects on fish fluctuations. Here, we collected published data to conduct a comparative analysis of time series in terms of both scale deposition rate (SDR) and catch to indicate the abundance of anchovy and explored its relationships with climatic and environmental parameters. We first conducted a Spearman correlation analysis to identify the differences in the SDR between sites. Then, we used Generalized Additive Models to evaluate the effects of external forcing at multiple spatial scales (i.e., local and global scales) on the anchovy catches recorded at the California Current Ecosystem (CCE), Humboldt Current Ecosystem (HCE), and Kuroshio Current Ecosystem (KCE). We found that the SDRs at different sites in the same Current Systems are generally consistent, while there are more differences between different systems. We also found that the Pacific Decadal Oscillation index (PDOI), North Pacific index (NPI), North Pacific Gyre Oscillation index (NPGOI), Sea Surface Temperature anomaly (SSTA), and Air Temperature anomaly (ATA) were the most influential factors explaining the variability in anchovy catch for CCE, whereas the NPGOI was the most influential factor for HCE. The PDOI was the best at explaining the variability in anchovy catch for KCE. Our results suggest that anchovy fluctuations in the Pan-Pacific occurred synchronously. These seemingly unrelated events, which occurred thousands of kilometers apart, were actually not isolated. Therefore, we suggest that large-scale climate forcing may activate synchronous fluctuations for anchovy populations at the basin scale, whereas local-scale environmental forces are also responsible for anchovy fluctuations in the “micro-environment”. Full article

The vast expanse of China’s land surface results in the country’s environment varying from region to region. Environmental changes impact on China’s industries, markets, and trade, indirectly affecting not only the country’s economy but also the people who depend on aquaculture resources. Regional differentiation leads to an imbalance that severely affects social fairness and equity, which becomes a key factor limiting the sustainable development of the economy and society. Analysis and assessment of the changes in environmental factors affecting aquaculture production and fisherfolk’s income in 31 regions of China between 2010 and 2020 aim to provide a reference for regional differentiation in the economic development of aquaculture in the different regions in China, representing an essential step towards achieving the coordinated development of rural regional areas. This study’s assessment and analysis procedures adopted the principal component analysis method. The findings suggest that regional differences in Chinese fisherfolk’s income and the environmental factors affecting China’s aquaculture production are veritable. There have been subtle changes in regional differentiation over a decade. It is necessary to implement contextualized environmental management measures, concessionary taxation, and additional subsidies to address the different characteristics of China’s different regions for the future development of environmental management and narrowing the income gap, to address both the income disparities in Chinese fisherfolk’s income and environmental factors affecting Chinese aquaculture production, to achieve the harmonious development of rural regional areas. Full article

Sthenoteuthis oualaniensis is an important biological resource in the South China Sea. However, the microbiological characteristics of this squid, especially those of the dwarf-form, are poorly understood. This study was conducted to analyze the microbial community structure and metabolic characteristics of the intestinal and gill tissues of dwarf-form populations of S. oualaniensis. The dwarf-form squids of different sexes and gonadal maturities were collected from South China Sea in spring 2020. Results showed that Mycoplasma was the most dominant group of bacteria in the intestinal samples of the females with immature gonads (FN), females at sexual maturity (FY), and males at sexual maturity (MY) and the second-highest relative abundance group in males with immature gonads (MN). The microbial community structure in squid gills differed from that of intestinal flora. The BD1-7 clade was the dominant genus in gill samples of all groups. Furthermore, the microbial community activities in gills were higher than in intestinal groups, especially FYG. The larger dwarf-form populations had microbial communities with more robust utilization of carbon sources, assessed via average well color development (AWCD). Correlation and redundancy analysis determined that AWCD significantly positively correlated with the relative abundance of BD1-7 clade (p < 0.05). The results indicated that the dominant group of bacteria and microbial community structure were different between the intestinal and gill microbial communities in the dwarf-form S. oualaniensis populations of different sexes and maturities. Moreover, the metabolic potential of the gill microbial community was higher than that of the intestinal microbial community in the dwarf-form populations. Full article

The effects of ultrafine bubbles on the high stock density of striped catfish larvae in a recirculating aquaculture system (RAS) are described in this research (UFBs-RAS). In this study, the various stock densities of striped catfish were investigated regarding the effect of oxygen saturation on the yolk sac absorption rate, length growth rate, and yolk sac utilization efficiency at the endogenous stage. The survival rate, the specific growth rate (weight, length, and biomass), and the gross feeding efficiency were examined at an exogenous stage. The results showed that the ultrafine bubbles generator in the recirculating aquaculture system (UFBs-RAS) provide the dissolved oxygen concentration up to 128.97%sat. The oxygen saturated state in FBs-RAS at the stock density 100 fish/L (D100) provided high yolk sac utilization efficiency in the endogenous stage and high survival, specific growth rate, and gross feeding efficiency in the exogenous stage. It was emphasized that the performance was possible due to surplus oxygen up to 1.58 mg/L at the stock density of 100 fish/L and accomplished minimum ammonia (NH₃-N) content much lower than the limit (0.12 µg/L). Thus, the striped catfish larviculture with UFBs-RAS-provided oxygen balance subsequently improved the production rate significantly with cost-effective production. Full article

Fish represent an excellent source of animal protein as well as a biomedical research model as a result of their evolutionary relatedness and similarity with the human genome. Commercial and ornamental fish culture has achieved popularity, but reproductive dysfunctions act as a limiting factor for quality fry production, interfering with the sustainability of the aquaculture industry. Fish reproduction is crucial for any species’ existence, and reproductive performance can potentially be improved through applications of epigenetics and probiotics. Epigenetics is a highly sensitive molecular approach that includes chromatin structure and function alteration, DNA methylation, and modification of non-coding RNA molecules for the transfer of desired information from parents to offspring. DNA methyltransferase improves reproductive cyp11a1, esr2b, and figla gene expression and feminizes zebrafish (Danio rerio). Moreover, epigenetics also contributes to genome stability, environmental plasticity, and embryonic development. However, methylation of specific genes can negatively affect sperm quality, resulting in poor fertilization. Probiotic administration is able to induce responsiveness of incompetent follicles to maturation-inducing hormones and can change oocyte chemical composition during vitellogenic development. The positive role of probiotics on testicular cells is validated by upregulating the transcription levels of leptin, bdnf, and dmrt1 genes facilitating the spermatogenesis. This review not only discusses the effects and mechanism of epigenetics and probiotics for improving fish reproduction, but also presents an overview of the causal factors and current techniques used to eradicate dysfunction. Moreover, key genes and hormones related to fish reproduction along with research gaps and future prospects are also considered. This review provides an overview of necessary information for students, scientists, researchers, and breeders to resolve fish reproduction-related problems to ensure profitable and sustainable aquaculture. Full article

The reproductive success of aquatic animals depends on a complex web of relationships between the environment, the attributes of the reproductive individuals and human-induced selection. All of them are manifested directly or indirectly through parental effects, which can also compensate for certain external impacts. Parental effects refer to the influence that the phenotype and environmental conditions in which individuals develop exert on the phenotype of their offspring, and they can even have transgenerational impact. This paper describes the different types of parental effects and reviews the published literature to analyze the causes of their variation and their impact on reproductive resilience and population dynamics. Full article

This study aimed to explore the feasibility of using an upper beak microstructure to estimate the age of purpleback flying squid (Sthenoteuthis oualaniensis). From these microstructures, the age and growth of squid caught from January to March and May to August in 2018, 2019, and 2020 in the waters surrounding the Xisha Islands in the South China Sea were determined. We found three typical growth zones (the hood region, crest region, and axis), abnormal increments (checks), and erosion in the beak examination. The average dorsal mantle length (ML) of males and females was 112.13 (±15.23 mm) and 119.67 mm (±24.50 mm), respectively, and no squid were older than 10 months. The peak hatching dates, according to back calculations, were from October to January of the next year. All sampled squid belonged to the autumn/winter cohort. Significant sex differences were found in the relationship between ML and age in squid with similar growth patterns. Exponential models best described the relationships of ML with age and body weight (BW) for both sexes. However, a linear model best described the relationship between age and upper rostrum length (URL). The maximum absolute daily growth rates (AGR) of BW were reached during days 240–270 for both sexes. The maximum AGRs in ML were reached during days 180–210 and 240–270 for males and females, respectively. The period of 120–150 days (4–5 months) was considered the sub-adult stage of S. oualaniensis in the Xisha Islands waters of the South China Sea. This study confirmed that the beak microstructure provides good age estimates for purpleback flying squid (S. oualaniensis). Full article

Global value chain (GVC) participation has played a significant role in boosting the trade gains of both developed and developing seafood-exporting countries over the past three decades. In addition, the extent of GVC participation has become the most important platform for addressing gains from trade in developing seafood-exporting countries to ensure that their participation enhances economic growth. Recent studies on GVC participation in developing countries have highlighted the importance of domestic institutions. However, the literature is silent on the quality of the domestic institutions–GVC participation nexus. This paper aims to investigate the determinants of GVC participation and the effect of the quality of domestic institutional governance on seafood-exporting developing countries’ GVC participation indices. Using the Hausman–Taylor (HT) estimator and the system generalised method of moments (GMM) dynamic panel data methodology to examine seafood export data from 32 countries from 2009 to 2018, we find that economic potential drives backward GVC participation, while low forward participation might not only lead to lower gains from trade, but also limit countries to the supply of primary seafood products with little value addition. In addition, the quality of domestic institutional governance constrains GVC participation. Overall the results indicate that the quality of domestic institutional governance matters for the GVC participation of seafood-exporting developing countries. Full article

Arachidonic acid (ARA, 20:4n-6) fed to Seriola dorsalis juveniles at different levels was evaluated. After a seven-week feeding trial, growth performance, hepatopancreas and muscle fatty acid (FA) composition, expression of lipid-relevant genes, and blood parameters were evaluated. Four isoproteic and isolipidic experimental diets were formulated to contain 44% crude protein and 11% lipids with graded inclusion levels of ARA, 0% (Control), 0.4, 0.9, and 1.4% of the total diet. S. dorsalis juveniles (14.54 ± 0.18 g) were randomly divided into twelve tanks with fifteen animals each. The animals were hand fed three times per day to apparent satiation. Dietary treatments did not significantly affect the growth performance, SGR, FCR, and feed intake of fish. Different levels of ARA in the experimental diets directly influenced liver and muscle FA profiles, with significant changes in ARA and EPA deposition between Control treatment and 1.4%, in both tissues. The expression of arachidonate 5-lipoxygenase (alox5), acyl-CoA dehydrogenase very long chain (acadvl), carnitine O-palmitoyltransferase 1(cpt1a) was significantly affected by dietary treatments, with an expression increasing accordingly to the increasing ARA levels. In contrast, a reduction of fatty acid synthase (fas) and proliferator-activated receptor alpha (ppara) expression was significantly reduced as ARA increased in the diet. In addition, a significant reduction in blood cortisol and glucose was found at a 0.9% ARA level compared to the other treatments. Based on the performance, cortisol levels, the gene expression for eicosanoids synthesis, and lipid metabolic pathways, the present study suggests a maximum ARA inclusion of 0.9% in diets for California yellowtail juveniles, S. dorsalis. Full article

The silky shark, Carcharhinus falciformis is one of the most heavily exploited sharks, being the main by-catch species in both tuna longline and purse-seine fisheries in tropical waters worldwide. Despite this severe exploitation, little is known about the species’ life history and population status. Silky sharks, like many other sharks, exhibit slow growth and low fecundity, indicating the urgency of developing assessment studies to aid in the implementation of conservation plans for their stocks. Because information on the catch and effort of this species is scarce, some length-based data-limited methods were applied in the present study to provide estimates of the status of the tropical Pacific silky shark population. As evident from the LBSPR analysis, the current spawning potential ratio (SPR) was found to be below the target reference point of SPR 40% and slightly above the limit reference point of SPR 20%. In addition, the LBB model also confirmed that this stock’s status is overfished with relatively low biomass levels. Furthermore, both models showed estimates of size selectivity at 50% and 95% that were lower than the estimated size at sexual maturity. In conclusion, the data-limited models developed in this study indicated that the silky shark stock in the tropical Pacific Ocean may be at risk of further decline. Additionally, the results show that growth and recruitment overfishing may be occurring in the silky shark’s population calling for immediate intensification of monitoring programs for these sharks as a pre-requisite to develop efficient management and conservation plans in the Pacific Ocean. Full article

After collapsing in the late 1990s, the southern Gulf of St. Lawrence population of striped bass (Morone saxatilis) is recovering. Here, we evaluate the use of under-ice eDNA sampling to monitor the population and confirm overwintering locations. From 2018 to 2020, water samples were collected from transects spanning 35 km of the Miramichi River system, accounting for the effects of sampling site, month, sampling depth and tidal influence on eDNA concentration. We examined the distribution of eDNA in a complex tidal river system with a time series consisting of 12 h of continuous sampling throughout a tidal cycle, in conjunction with the use of artificial DNA tracers and acoustic Doppler current profiler flow measurements. The eDNA distribution correctly identified overwintering grounds based on acoustic tag data, including a perceptible upstream shift in 2020. Overall, there was no significant effect of year, sampling month (February or March), sampling depth or tidal phase on eDNA concentrations. The tidal time series revealed only weak patterns of eDNA recirculation. Monitoring eDNA concentration and distribution allows for a relative comparison of population size and location between years, and has the potential to be expanded to other river systems more easily than traditional acoustic fish tags and surveys. Full article

Mitten crab, Eriocheir sensu stricto, is an important indigenous aquatic species and food source in Eastern Asia. Genetic diversity is an important prerequisite for the conservation and utilization of germplasm resources. However, the genetic diversity and differentiation of Eriocheir s. s. remains unclear. This study evaluated population genetic diversity and genetic differentiation of three Eriocheir s. s. populations from Suifenhe (SFH), Liaohe (LH), and Nanliujiang (NLJ), China, based on 19 microsatellite markers. The mean observed number of alleles (N_a) was 22.84 alleles, and the mean polymorphism information content (PIC) was 0.86, which demonstrated high genetic diversity. The allele frequency distribution showed an “L” shape, ranging from 0.01 to 0.74. The genetic diversity parameter values of the LH population were higher than those of the other two populations. All pairwise F_ST values showed significant differences among the three Eriocheir s. s. populations (p < 0.01). The value of Nei’s genetic distance (D_S) varied from 0.31 (between SFH and NLJ populations) to 0.33 (between SFH and LH populations). Overall, The results illustrate that the three wild Eriocheir s. s. populations have high genetic diversity and high genetic differentiation. This study provides the basis for Eriocheir s. s. utilization in China. Full article