Fishes, Volume 8, Issue 5 (May 2023) – 57 articles

Pre-harvest male maturation is problematic for Atlantic salmon (Salmo salar) farmers and is regulated by the environment and genetics (e.g., vgll3). Five families of all-male salmon parr (produced using YY males crossed with XX females) with different vgll3 genotypes were split between three environmental regimes in January 2018. The “advanced maturation” regime used elevated temperature (16 °C) and continuous light from January 2018 with post-smolt maturation assessed in March 2018. The “extended freshwater” regime used ambient freshwater (1–16 °C) and simulated natural photoperiod (SNP) with post-smolt maturation assessed in November 2018. The “sea transfer” regime used ambient temperatures (1–14 °C) and SNP in freshwater until May 2018 when they were transferred to 9 °C seawater with natural photoperiod for 2.5 years (final mean weight of circa. 14 kg) and assessed for post-smolt maturation, 1 sea-winter (1 SW) maturation, and 2 sea-winter (2 SW) maturation in the autumn (November/December) of 2018, 2019, and 2020, respectively. Post-smolt maturation was highest in the advanced maturation and extended freshwater regimes (39–99% depending on family) and lowest in the sea transfer regime (0–95% depending on family). In the sea transfer regime, maturity incidence increased over time (0–95% post-smolt maturation, 1–100% 1 SW, and 50–90% 2 SW maturation, depending on family). In all regimes, those homozygous for the pre-designated vgll3 “early” maturing allele had the highest incidences of maturation whilst those homozygous for the “late” allele had the lowest. A low percentage of 2 SW phenotypic and genetic females were found (0–5% depending on family), one of which was successfully crossed with an XY male resulting in progeny with an approx. 50/50 sex ratio. These results show (i) post-smolt maturation varies dramatically depending on environment although genetic regulation by vgll3 was as expected, and (ii) crossing YY sperm with XX eggs can result in XX progeny which can themselves produce viable progeny with an equal sex ratio when crossed with an XY male. Full article

The coastal waters of French Guiana are amongst the most turbid and nutrient rich in the world, and as such, they favour the settlement and early development of several species of marine fish. Recent work has revealed a high abundance of Atlantic Goliath Grouper (Epinephelus itajara) in these waters, yet little is known about this species’ reproductive biology, which this study aims to complement. During the period from 2010 to 2013, we surveyed Goliath Grouper at three rocky sites along the French Guiana coast and examined 602 individuals for evidence of maturation. Satellite tags were deployed on five individuals and an acoustic survey was conducted to identify potential spawning movements and activity. We found no evidence of sexually active individuals or local spawning aggregations. Most individuals showed high site fidelity, but one fish was located 1150 km away, near Trinidad and Tobago. We discuss these findings in the context of the wider literature and postulate that Goliath Grouper inhabiting French Guiana reefs originate from spawning sites in northern Brazil and disperse to westerly reefs with the onset of maturity. We propose that the Goliath Grouper populations of South America and Caribbean are linked, and that management of Brazilian source populations could have wide-reaching impacts on Goliath Grouper stocks. Full article

Mozambique tilapia Oreochromis mossambicus (Peters, 1852), an important aquaculture species investigated herein, is at risk and listed as vulnerable on the IUCN Red List. During a preliminary survey conducted in 2011, 30 Mozambique tilapia from Lake Urema in Gorongosa National Park in central Mozambique, were examined for metazoan parasites. Two groups of ectoparasites were recovered consisting of two species of copepods and a monogenean. Endoparasites retrieved were in the larval stage and included one trematode and one nematode species. This study provides new parasite records for O. mossambicus in Mozambique and forms a baseline for monitoring against the presence of ichthyoparasites associated with the introduction in neighbouring systems of non-native fish such as Nile tilapia Oreochromis niloticus (Linnaeus, 1758), a fish of worldwide importance in capture fisheries and especially aquaculture. Full article

In a context in which climate change, overexploitation, and environmental degradation are continuously progressing, the sustainable use of the sea is a key target, both for resources and fishery operators. With the aim of enhancing the sustainability and competitiveness of the entire fishery sector, an innovation brokering event was organized. Via the application of a participatory, interactive, and bottom-up approach, different actors in the Italian SSF sector were stimulated to work together to find innovative solutions to day-by-day problems. During the consultation, and between the identified problems, emerged the lack of cooperation for marketing activity and effective strategies for seafood product development. A pilot action consisting in co-designing a virtual marketplace (VirMa) was the result of the event, intending to facilitate the direct sale of seafood products, explore this new and valuable market, and establish a direct line with consumers. The VirMa application was developed as a value chain network, trying to add value to seafood products. However, an information and communication tool, such as a VirMa, could contribute to increasing the resilience of the SSF sector to market constraints even during unforeseen events, such as a pandemic. Full article

Chondrichthyes (including sharks, rays, and chimaeras) are a class of jawed cartilaginous fishes (with skeletons composed primarily of cartilage), with major relevance to the marine ecosystems and to humanity. However, cartilaginous fishes are facing various threatens, inflicting abrupt declines in their populations. Thus, critical assessment of available molecular genetic variation, particularly retrieved from Chondrichthyans’ transcriptomic analyses, represents a major resource to foster genomics research in this ancient group of vertebrate species. Briefly, RNA-Seq involves the sequencing of RNA strands present on a target tissue, which can assist genome annotation and elucidate genetic features on species without a sequenced genome. The resulting information can unravel responses of an individual to environmental changes, evolutionary processes, and support the development of biomarkers. We scrutinized more than 800 RNA-Seq entries publicly available, and reviewed more than one decade of available transcriptomic knowledge in chondrichthyans. We conclude that chondrichthyans’ transcriptomics is a subject in early development, since not all the potential of this technology has been fully explored, namely their use to prospectively preserve these endangered species. Yet, the transcriptomic database provided findings on the vertebrates’ evolution, chondrichthyans’ physiology, morphology, and their biomedical potential, a trend likely to expand further in the future. Full article

Cantharidin, a toxic monoterpene secreted by blister beetles, has long been used in traditional Chinese and modern medicine for its unique properties. However, despite its widespread use, its effects on fish have not been studied. The aim of this study was to evaluate the potential therapeutic applications of cantharidin in fish by examining its antioxidant, hemagglutinating, hemolytic, and cytotoxic activities at different concentrations (0, 0.625, 1.25, 2.5, 5, and 10 μg mL⁻¹) in three different cell lines. In addition, the study explored the bactericidal and bacteriostatic properties of cantharidin against various fish pathogenic bacteria. The results revealed that there were no significant differences in antioxidant, hemagglutinating, or hemolytic activities between the different concentrations of cantharidin tested. However, the study found that cantharidin exhibited dose- and time-dependent cytotoxicity in seabream (Sparus aurata) erythrocytes and in SAF-1, PLHC-1, and Hela cell lines, resulting in morphological changes indicative of apoptosis. Interestingly, the highest dose of cantharidin tested demonstrated potent bactericidal activity against four marine fish opportunistic bacteria, including Vibrio harveyi, V. anguillarum, Photobacterium damselae, and Tenacibaculum maritimum, but no statistically significant changes in bacteriostatic activity were observed against any of the bacteria tested. Overall, these results provide valuable information on the potential therapeutic applications of cantharidin in fish aquaculture. Further research is needed to fully understand the mechanisms of action and to explore possible preventive uses of cantharidin in fish. Full article

The weight–length relationship (WLR) of fish is a crucial tool in fish biology research and has received extensive attention. However, fish growth is influenced by many factors, and the WLR also changes accordingly. Our aim was to investigate how fish body shape is affected by various factors by analyzing the existing parameters of the relationship between fish body length and weight. We analyzed 198,354 fish specimens belonging to 402 species of 82 families in China and investigated the change of fish body shape in the function of their ecology. Herbivorous fish tended to be shorter and fatter than carnivorous fish, and omnivorous fish fall somewhere in between. This difference could be due to variations in feeding habits and the availability of food sources. Additionally, fish living in lentic waters tended to have a shorter and fatter body shape compared to those living in lotic waters. This could be attributed to differences in swimming behavior in these environments. Furthermore, our results showed that the b value decreased as altitude increased, and fish tended to be thinner and longer due to lower oxygen and temperature levels in high-altitude waters. Overall, our study provides valuable insights into the WLR of fish and the impact of multiple factors on fish body shape. Full article

The identification of sustainable materials as an alternative to plastic is fundamental for the protection of the environment and for the safeguard of marine ecosystems. The replacement of plastic with organic materials for fish storage might affect its shelf-life due to the high concentration of oxidizable fatty acids in fish flesh. This study investigated the effectiveness of two organic packaging materials, namely coconut fiber (Coc) and paper (Pap), as alternatives to the conventionally used polystyrene (Pol), on the shelf-life, hygienic parameters, and quality traits of anchovies refrigerated for one (T0), three (T1), or seven (T2) days. The hygienic quality of anchovies packaged in the organic Pap and Coc boxes was better than the traditional Pol, probably due to the higher porosity of the packaging, which allows a higher bacterial proliferation. Results of the T-BARS test showed a lower (p < 0.05) malondialdehyde concentration in fillets from the Pap group, which increased (p < 0.05) from the first to the seventh day of storage. The polyunsaturated fatty acids concentration did not differ between groups, but it decreased (p < 0.05) from T0 to T2. Coconut fiber and paper are worthy of further investigation since these packaging materials did not affect the shelf-life and fatty acid profile of anchovies during storage. Full article

In this study, we investigated the effects of cortisol on the regulation of the glycogen metabolism biomarkers glycogen synthase (GS) and glycogen phosphorylase (GP) in the glycogen-rich cells of the gills of tilapia (Oreochromis mossambicus). In the gills of tilapia, GP, GS, and glycogen were immunocytochemically colocalized in a specific group of glycogen-rich cells adjacent to the gills’ main ionocytes and mitochondria-rich cells. Cortisol plays a vital role in the regulation of physiological functions in animals, including energy metabolism, respiration, immune response, and ion regulation. However, no studies have elucidated the mechanisms regulating cortisol and glycogen-rich cells in the gills. Therefore, we treated tilapia larvae with exogenous cortisol and a glucocorticoid receptor (GR) antagonist to investigate the regulatory mechanisms between cortisol and glycogen-rich cells in the gills. Our results showed that cortisol promoted the expression of gill glycogen phosphorylase isoform (GPGG) mRNA via GR, whereas the GS gene expression remained unaffected. We also found that GR mRNA was colocalized with some glycogen-rich cells in the gills, further confirming our hypothesis that cortisol directly acts on glycogen-rich cells in the gills of tilapia and regulates glycogen metabolism by promoting GPGG mRNA expression. Full article

About 11 million marine ornamental fish of ca 1800 non-native species are imported into the USA each year. Selecting species for risk assessment is daunting for such a diverse pathway. Herein, we discuss a focused method for species selection: choosing important taxa related to known invaders in high-volume pathways and narrowing prospective species lists to manageable groups of potential hazards. We provide an example using 11 damselfishes, a family with high volume in trade and one of the species established in USA waters. We used a specialized literature review and a risk screening tool (Aquatic Species Invasiveness Screening Kit) to provide an estimate of risk of invasiveness of marine waters of Florida. The established species was identified as a hazard and potential invasive. All other species scored well below the threshold for invasiveness and future climate had little effect on estimates of invasiveness. The analysis revealed little need for additional risk assessment or prohibitions on damselfishes in trade. Education, monitoring, and early detection and rapid response were the main risk management recommendations. The focused species selection process employed herein provided hazard identification and preliminary risk estimates for just 11 species, but collectively, they represent 40% by volume of fishes imported in the marine ornamental trade. Full article

The health of aquatic organisms can be affected due to anthropogenic activities and limited actions to reduce the pollution of the Black Sea. The accumulation of organic pollutants (OPs) in the aquatic environment occurs in water, sediment, and then biota. The turbot (Scophthalmus maeoticus) is a benthic fish of commercial interest scarcely studied in the Black Sea region, and none of the studies researched OP concentrations in its main tissues. In this paper, polycyclic aromatic hydrocarbons (PAHs) and POPs, organochlorine pesticides (OCPs) and polychlorinated biphenyls (PCBs) were determined in water, sediment, and turbot muscles, gills, gonads, and livers, to research their accumulation level. The determinations were made with gas chromatography on turbots sampled in 2021 from the Romanian Black Sea waters. OCPs—p,p’DDT and its metabolites p,p’DDE, p,p’DDD—are dominant in the turbot tissues. From PAHs, benzo(g,h, i)perylene was the dominant compound, while for PCBs it was PCB 52. The OPs’ presence in the wild turbot is due to river input, dredging and coastal rehabilitation works, industrial activities and contaminated food and poses a risk to human health due to the exceeding maximum allowable concentration for human consumption in Romania and the European Union. Full article

Microencapsulation is an advanced technique used to improve the viability of probiotics and minimize sensitivity during processing, storage, and in the gastrointestinal environment. Two dietary treatments including a control and an encapsulated probiotic, Bacillus subtilis E20 (EP), were used to evaluate the efficacy in improving the intestinal microbiome of white shrimp, Penaeus vannamei, after a 60-feeding trial. The 16S rDNA next-generation sequencing (NGS) analysis indicated that shrimp fed the EP diet generated higher amplicon reads than shrimp fed the control diet. No significant differences were observed in the α-diversity index of the intestinal microbiota of shrimp that were fed the control and EP diet. At the phylum level, Proteobacteria was relatively abundant in the microbiota of shrimp fed both the control and EP diet. The treatment with EP increased the expression of Tenericutes, Bacteroidetes, and Firmicutes, more than the control. The PC analysis revealed that the EP diet altered the bacterial profile in shrimp’s intestines into forming different clusters. Unique genera such as Luteolibacter, Simkaniaceae, Haemophilus, Pirellulaceae, Filomicrobium, Sphingomonas, and Erysipelotrichaceae UCG-003 along with well-known probiotic genera Bacillus and Lactobacillus were found in the intestine of shrimp fed the EP diet. The PCA eigenvector plots indicated a higher abundance of Bacillus in shrimp fed with EP diet, but a higher abundance of Vibrio in shrimp fed with control diet. These results suggest that encapsulated B. subtilis E20 can be beneficial to shrimp microbiota. Full article

Trichiurus japonicus is an economically important fish that ranks 11th in global marine fish capture production. However, the reproductive characteristics of this fish have undergone notable changes in recent decades, potentially affecting the quality of offspring and sustainable utilization. To improve our understanding of the physiological regulation of maturation in T. japonicus, untargeted liquid chromatography mass spectrometry was utilized to identify the small molecules that characterize the comprehensive metabolic profiles of ovaries during ovary development from stage II to stage IV. According to the results of OPLS-DA, the ovarian metabolite profiles of the three developmental stages were separated. The concentrations of 124 and 100 metabolites were significantly altered between stage II vs. III and III vs. IV, respectively. Lipids and lipid-like molecules accounted for the largest proportion of the altered metabolites, followed by amino acids, peptides, and analogues. The significantly altered metabolites-enriched pathways differed slightly between stages II and III and stages III and IV. Steroid-related pathways were heavily affected during stages II to III, while significantly altered metabolites from stages III to IV were involved in oocyte-maturation-related pathways. Through metabonomics analysis, potentially important metabolic pathways and metabolites between different ovarian stages were detected, providing basic information for further investigation of maturation mechanisms in wild fish. Full article

Understanding the diet of whale sharks (Rhincodon typus) is essential for the development of appropriate conservation strategies for the species. This study evaluated the use of the parasitic copepod (Pandarus rhincodonicus) as a proxy to infer short-term foraging habitats and trophic positions of whale shark hosts. To accomplish this, bulk stable carbon (δ¹³C) and nitrogen (δ¹⁵N) isotope compositions were analysed from 72 paired samples of whale shark skin (dermal) tissues and copepods collected across six years at the Ningaloo Reef aggregation site, Western Australia. This study found that δ¹⁵N from parasites and whale shark hosts were strongly correlated. As turn-over times of the parasite and whale shark differ (months vs. years, respectively), the ability of copepods to predict δ¹⁵N values indicates that the trophic positions of whale sharks remain consistent across these timeframes. Contrastingly, δ¹³C in the parasite and host were weakly correlated, likely reflecting differences in the physiology and lifecycle of the copepod parasite compared to the host. Our results suggest δ¹⁵N from parasitic copepods provides a reliable proxy of the trophic position of their whale shark hosts, but interpretation of δ¹³C values as a proxy for the host will require future studies on the lifecycle of P. rhincodonicus. Full article

The literature suggests regional variations in the size at which sexual maturity is reached for commercially important edible crab (Cancer pagurus), worth GBP 74.3 million annually, which could have implications for regional fisheries management. Berwickshire and Northumberland are geographically divided by the Scotland and England border and remain within the Berwickshire and North Northumberland Coast SAC (Special Area of Conservation). Each are managed by differing fisheries authorities and Minimum Conservation Reference Sizes (MCRS). Morphometric measurements were recorded for each C. pagurus individual to categorise morphometric maturity using segmented regression, with gonadal maturity categorised using visual gonad characteristics and general linear model regressions to compare onset in sexual maturity. Results showed regional variations for gonadal maturity with males reaching sexual onset at a carapace width size of 108.5 mm in Berwickshire and 109.9 mm in Northumberland; females at a size of 126.8 mm in Berwickshire and 120.8 mm in Northumberland. This was also true for morphometric maturity based on chelae height, that males (141.1 mm) and females (134.7 mm) from Berwickshire were morphometrically mature at greater sizes than males (130.1 mm) and females (120.8 mm) from Northumberland. This study shows that the respective MCRS in both regions are appropriate for the C. pagurus populations, but implications for fisheries management could be present. Full article

A 10 week feeding trial was conducted to evaluate the potential effects of ginger powder (GP) and ginger extract nanoparticles (GNPs) on the growth parameters, digestive enzymes (lipase and amylase) activities, blood hematology, blood biochemical indices, immune indices (interleukin 10, immunoglobulin M, nitric oxide, and lysozymes), antioxidant activity, histological characteristics of kidney, spleen, liver, and intestine, and resistance to Aeromonas hydrophila or Pseudomonas putida infection in Nile tilapia, Oreochromis niloticus. Fish (n = 225, 27.01 ± 0.15 g) were stocked in 15 glass tanks (50 × 40 × 60 cm) and randomly allocated to five experimental treatments (TRTs) in triplicate (15 fish/replicate, 45 fish/TRT), consisting of five isocaloric–isonitrogenous diets. The treatments comprised the basal diet (1) without any additives (control group, CON), (2) with 0.5% GP (GP0.5), (3) with 1% GP (GP1), (4) with 0.5% GNPs (GNPs0.5), and (5) with 1% GNPs (GNPs1). Fish were manually fed to satiety three times a day (at 9 a.m., 12 p.m., and 2 p.m.). Fish were weighed at the start of the experiment, then the body weight, weight gain, feed intake, and feed conversion ratio were determined at the end of the experiment. At the end of the feeding period, 15 fish/TRT were intraperitoneally inoculated with two pathogenic bacterial strains (A. hydrophila or P. putida) in two separate challenge tests. Blood samples were collected from each TRT at two aliquots for hematological and biochemical analysis at the end of the feeding period. A significant improvement in fish growth was observed in GP and GNPs TRTs compared to the control group. There were no significant changes in the total amount of feed intake/fish in response to the experimental diets. Diets enriched with GNPs, particularly the GNPs1 TRT, resulted in a significant increase (p < 0.05) in digestive enzyme activity (lipase and amylase), serum growth hormone level, proteinogram, and immune indices (lysozyme, immunoglobulin M, interleukin 10, and nitric oxide). In addition, a significant increase in hepatic antioxidant enzymes (superoxide dismutase, reduced glutathione, and catalase) was observed in fish fed with GNPs-enriched diets. Survival percentages following bacterial challenge were higher in GNPs1, followed by GP1 and GNPs0.5 TRTs. Normal histomorphology was found in liver, kidney, and spleen tissues in all experimental TRTs. We conclude that GP and GNPs could be included in Nile tilapia diets for promoting fish growth, immunity, antioxidant status, and disease resistance without harming organ functions. In particular, the most effective treatment was GNPs1. Full article

Japanese eels (Anguilla japonica) are a typical migratory fish species with high commercial importance. The Pearl River estuary in southern China is an important natural growing ground for Japanese glass eels, but limited information on Japanese glass eel population characteristics is available, despite their ecological importance. In this paper, we examined the annual patterns of the occurrence of Japanese glass eels in the Pearl River estuary from 2011 to 2022. The most frequently occurring Japanese glass eel’s total length is 5.3 cm. The collecting period extended from December to February, and the collection catch-per-unit-effort (CPUE) decreased significantly from 2011 to 2022. The generalized linear model (GLM) indicated that daily changes in Japanese glass eel collection were significantly affected by tidal range, water temperature, and lunar distance. The catch peak appeared when the tidal range rose to 1.7 m, and the water temperature dropped below 8 °C on the full moon days. Overall CPUE analysis showed no significant periodic and inter-annual variability in the period 2011–2022, with the ARIMA model suggesting that the CPUE is expected to remain stable but low in the coming years (2023–2026), although recruitment ultimately depends on the overall spawning stock. Full article

Here, the olive leaf extract (OLE) rich in polyphenols was employed as a prebiotic agent, together with Lactobacillus reuteri and Bacillus clausii, to develop synbiotics. The prebiotic effect of olive leaf extract on the probiotic strains was tested at concentrations of 0, 50, 100, 400, and 1000 μg mL⁻¹, and also 20 and 40 mg mL⁻¹. Olive leaf extract at 40 mg mL⁻¹ showed the best prebiotic activity on L. reuteri and B. clausii. A basal diet and two experimental synbiotic-containing diets were prepared. The synbiotic diets were manufactured by adding to the basal diet 5 × 10⁶ CFU g⁻¹ L. reuteri + 5 × 10⁶ CFU g⁻¹ B. clausii + 0.25 mg g⁻¹ OLE and 1 × 10⁷ CFU g⁻¹ L. reuteri + 1 × 10⁷ CFU g⁻¹ B. clausii + 0.25 mg g⁻¹ OLE. The diets were administered to the freshwater crayfish Astacus astacus (1.35 ± 0.04 g) in an 84-day feeding trial. The diet containing 5 × 10⁶ CFU g⁻¹ L. reuteri + 5 × 10⁶ CFU g⁻¹ B. clausii + 0.25 mg g⁻¹ OLE significantly improved (p < 0.05) final weight, specific growth rate, body condition, and survival rate. A significant growth of Enterobacteriaceae, which include strains with proven beneficial activities for intestinal health and general animal welfare, significantly increased in crayfish fed with synbiotics. The obtained results could be suitable for functional feed development in crayfish farming. Full article

Extra-Poisson variance in annual reproductive success can affect the precision of abundance estimates made using ‘close-kin’ mark–recapture procedures. However, empirical evaluation of that variance in natural marine populations can be daunting. Here, a scaling method was used to extend a discrete-time, age-structured model, facilitating investigation of annual and lifetime reproductive success dynamics in Epinephelus itajara. Life tables were synthesized from fishery assessment vital rates and life history measures. For model scaling, a precise empirical estimate of effective population size for the studied population was utilized as the independent variable, and model sensitivity to an informative range of adult abundance was evaluated. The potential for sex reversal to impact reproductive success dynamics was also investigated, albeit in the absence of selective fishing pressure and potential compensatory or depensatory responses. Close-kin relationships in a genetic sample of ~300 adults collected from spawning sites in the Florida Atlantic included numerous full-sibling pairs and multi-sibling families, which is unusual for long-lived, iteroparous marine populations with broadly dispersed larvae. The highly overdispersed reproductive success dynamics modeled for this population and its atypical kinship distribution could have ramifications for planned close-kin mark–recapture analyses. The low observed effective size also has conservation implications. Both issues warrant continued genetic monitoring. Full article

Recently, the economic traits of Chinese mitten crab (Eriocheir sinensis) varieties have had a negative tendency. Meanwhile, the status of wild germplasm resources of E. sinensis is unknown, hindering the utilization of wild germplasm resources and the green development of the E. sinensis industry. Thus, the conservation of the wild E. sinensis germplasm resource is of great significance. To this end, we collected wild E. sinensis from two different river basins, the Yangtze River basin, and the Liaohe River basin, and analyzed the genetic diversity as well as the genetic differentiation in E. sinensis populations. Based on eight microsatellite markers, we found moderate genetic diversity in E. sinensis populations regardless of river basin. Based on the mitochondrial D-loop region, we found that all populations are at mutation drift equilibrium, while the Nm between any two populations is greater than 1. We hypothesized the existence of island model gene flow patterns among E. sinensis. Interestingly, genetic differentiation among E. sinensis populations was low, except that between Liaohe and Anqing or Shanghai populations. Additionally, geometric morphological analysis could distinguish E. sinensis from different basins, with an accuracy of 94.2–100%. Given the similar genetic diversity in the two basins, the genetic convergence of E. sinensis from different basins deserves further attention. Full article

Piscine orthoreovirus genotype 1 (PRV-1) is an endemic virus to the Northeastern Pacific that infects both wild and farmed salmon. To better understand PRV-1 prevalence and transmission pathways in the region, we targeted out-migrating juvenile Pacific Salmon in the Strait of Georgia and Johnstone Strait in British Columbia, Canada, for PRV-1 molecular screening with an emphasis on Chinook (Oncorhynchus tshawytscha) and Coho (Oncorhynchus kisutch) salmon. A total of 4031 individuals were screened for PRV-1 and we identified an overall virus prevalence of 3.5% from 2011 to 2020. PRV-1 was absent in enhancement facilities and freshwater catchments and predominately found in the marine environment. The detection of PRV-1 varied greatly between species, year and stock of origin, but cumulatively identified that life history and migratory behaviors likely influenced viral prevalence. Specifically, Chinook salmon, which demonstrate long residence time in the Strait of Georgia relative to other species, had the highest PRV-1 prevalence in this study (7.4%). Varying stock composition and regional detection between year classes within the Strait of Georgia further indicated that the sources for Chinook infection were highly variable between years. These findings enhance our understanding for PRV-1 transmission in the region and more generally between/within salmon species. Full article

The aim of this study was to evaluate the potential effects of γ-irradiated date palm fruit (Phoenix dactylifera), which is rich in phenolic acids and has important and varied biological bioactivities, on growth performance, mucosal immunity and liver antioxidant status in goldfish (Carassius auratus). The antioxidant activity, alongside the phenolic and flavonoid contents, were also determined in irradiated palm fruit extracts (IPFE). The results showed that IPFE5 had a higher antioxidant activity as well as heightened phenolic and flavonoid contents compared to IPFE10 and IPFE0. Meanwhile, goldfish specimens were randomly divided into three groups with three replicates in each. Subsequently, skin immunity and antioxidant activity in the livers of the goldfish were studied. The growth rates of fish fed with IPFE5 and IPFE10 were significantly higher (p < 0.05) compared to the CTR group. In addition, fish fed with the IPFE5 diet demonstrated increased mucosal immunity compared to the CTR group (p < 0.05). Lipid peroxidation levels as well as antioxidant enzyme activities were also higher in all the IPFE-fed groups compared to the CTR group (p < 0.05). These data showed that 40-day dietary administration of γ-irradiated date extract, especially IPFE5, improved growth performance, mucosal immunity, and liver antioxidant capacity in goldfish. The suitability of administrating this additive in the diet of farmed fish is discussed. Full article

Hybrid sturgeon is an important economic fish species in China. In 2021, a bacterium was isolated from the liver and kidneys of freshwater-farmed hybrid sturgeon in Yichang City, Hubei Province, causing a disease with high mortality and surface bleeding. Through morphological observation, 16S rDNA gene sequence analysis, pathogenicity, an antimicrobial sensitivity test, as well as serum physiological and biochemical analysis, it was identified as Staphylococcus saprophyticus and named E702. The 16S rDNA gene sequence of E702 is highly homologous to S. saprophyticus in GenBank. Phylogenetic analysis showed that E702 and S. saprophyticus clustered into one clade. The 50% lethal dose of E702 was 2.14 × 10⁵ CFU/g. The percentages of monocytes and eosinophils were markedly increased in the diseased sturgeon’s blood, whereas the percentages of platelets and lymphocytes were decreased. The activity levels of aspartate aminotransferase, alanine aminotransferase and alkaline phosphatase in the diseased fish were significantly increased. The diseased fish suffered obvious damage to many tissues and organs, especially the liver and kidney, showing swelling, hyperemic and inflammatory cell infiltration. E702 was sensitive to antibiotics such as neomycin, cefazolin, norfloxacin, carbenicillin, gentamicin and ciprofloxacin. The study not only proved that S. saprophyticus was responsible for a great deal of hybrid sturgeon deaths, but also shed light on its potential risks in hybrid sturgeon farming. The research results provided the theoretical basis for the diagnosis as well as prevention of this disease. Full article

Mesanophrys sp. is reported to be highly pathogenic to marine crustaceans. This study presents the first report of Mesanophrys sp. infection in the mud crab (Scylla paramamosain). In this study, we first recorded the survival rates of an experimentally infected group and a control group; the cumulative survival rate in the infected group was significantly lower compared to the control group after 72 h (73.20% vs. 94.19%), while the highest mortality of S. paramamosain occurred within the first 24 h post-infection. Then, we investigated the dynamic distribution and tissue tropism of the Mesanophrys sp. in the infected S. paramamosain by a quantitative real-time polymerase chain reaction (qPCR). The result showed that a significant increase in the number of Mesanophrys sp. could be detected in all tested tissues (obtained from the eyestalks, gills, heart, nerves, muscles and hepatopancreas) at 3 h post-infection. The numbers of Mesanophrys sp. in the gill, eyestalk and nerve tissues were relatively higher than in the other tissues. The gill tissue showed the highest numbers from 6 to 48 h. Histopathological observation found a severe collapse in the filament structure, which indicated tissue-specific pathogen infection. Furthermore, the antioxidant enzyme activity of superoxide dismutase (SOD), catalase (CAT) and peroxidase (POD) in three representative tissues (gill, muscle and hepatopancreas) were compared between the infected and control groups, and a significant increase in enzyme activity was observed in all three tested tissues in the infected group, indicating a relatively strong innate immune defense reaction that could have been induced by Mesanophrys sp. infection. These results will be helpful to Mesanophrys sp. pathogenicity-related research and the control of this pathogen in S. Paramamosain in the future. Full article

Artificial reefs (ARs) have been advocated for and implemented as management tools for recreational fisheries, species conservation, and habitat replacement; however, the research that includes attracting marine species of floating ARs remains in its early stages. Here, two types of floating ARs were designed to evaluate the attractive effects using the occurrence rate and attracting index for six commercially important species (Lateolabrax maculatus, Liza haematocheila, Sebastes schlegelii, Acanthopagrus schlegelii, Litopenaeus vannamei, and Amphioctopus fangsiao) in the Bohai Bay of China; their combined ARs were meanwhile compared with two variants of artificial seagrass beds (SA and SB) and the traditional double-frame artificial reef (TD). All of the designed ARs were effective in attracting experimental species. The ARs with higher shelter areas (SB and TD) showed a better attracting effect. The efficiency of the ARs in attracting different species depended on their life histories. The bottom-mounted ARs were more efficient in attracting demersal species, while the floating ARs attracted epipelagic fish. In addition, the combined reefs had a better attractive effect than single ARs did. Overall, floating ARs and their combined ARs show the potential to deploy especially for attracting epipelagic fishes, although further study is needed. Full article

Beneficial microorganisms can increase nutrient digestion and absorption in farmed fish. This study investigates the effects of supplemental feeding of Bacillus species isolated from the intestines of wild glass eels on the growth, survival, and gene expression of farm-raised eel larvae for 30 days after hatching. Three species of Bacillus (B. velezensis, AJBV; B. subtilis, AJBS; B. licheniformis, AJBL) without hemolytic activity were isolated, and an experiment compared the growth of eel larvae fed an artificial diet supplemented with each Bacillus species. There were no significant differences in the total length and body depth of eel larvae at 30 days after hatching in all groups. During the feeding period, 149 eels survived from the initial 1000 in the control group. On the other hand, 240, 178, and 141 eels survived in the AJBV, AJBS, and AJBL groups, respectively. However, there were no significant differences in survival rates despite the difference in the number of surviving eel larvae among the groups. In the comparison of gene expression of genes involved with growth (growth hormone, growth hormone receptor 1, insulin-like growth factor II-2) and those involved with digestive enzymes (amylase, trypsin, lipase), there were also no significant differences among the groups. Our results confirm that dietary supplementation with each of the three host-associated Bacillus does not affect the growth and survival rates of eel larvae reared on an artificial diet up to the first 30 days after hatching, nor does it significantly affect related gene expression. Full article

The demand for jellyfish is growing worldwide, especially due to their high nutraceutical value. In this study, the extraction and characterization of crude gelatin from the brown cannonball jellyfish (Stomolophus meleagris), which is periodically found in large volumes on the American Pacific coasts, were carried out. The crude gelatin obtained by alkaline treatment, with subsequent heat and dialysis treatment, showed an ability to quench free radicals (via ABTS and ORAC methods), and protect human cells against oxidative damage (through inhibition of hemolysis by AAPH), and they protected against mutations caused by aflatoxin B₁ in the Salmonella enterica Typhimurium TA100 strain. Furthermore, it was established that these extracts were innocuous for eukaryotic cells (genotoxicity assay). The amino acid profiles indicate a high concentration of glycine and proline, as well as charged amino acids. Electrophoretic, FT-IR, and ¹H-NMR studies indicated that one of the main proteins present in this crude gelatin is collagen. The presence of collagen and other proteins was identified by proteomic studies. Alkaline crude gelatin from brown jellyfish could be considered as potential candidates to be evaluated as antioxidant agents in foods in future research. Full article