Fishes, Volume 8, Issue 8 (August 2023) – 43 articles

The Bagridae fish family holds significant economic value and enjoys a high demand in the commercial market due to its desirable characteristics, such as delicious meat, fewer muscle spines, and a pleasing flavor. In recent years, the Bagridae has experienced rapid development in the seed industry in response to industry demands. Researchers have conducted extensive studies on genetic breeding in the Bagridae, employing a comprehensive breeding approach that combines conventional breeding techniques with innovative new technologies and cooperative efforts. In this review, we present an overview of the market situation and discuss various breeding processes applied to the Bagridae, including selective breeding, genetic engineering breeding, cell engineering breeding, molecular marker-assisted breeding, and hybrid breeding. Additionally, we focus on introducing the cultivation methods for two new Bagridae varieties. Furthermore, we explore and summarize the breeding conditions, genetic background, heterosis, comprehensive breeding technology, stress resistance, and metabolic nutrition of hybrid Bagridae catfishes. Overall, noticeable heterosis has been observed in the breeding of the hybrid yellow catfish “Huangyou-1”, which exhibits promising market prospects and economic benefits for aquaculture. Our study aims to underscore the importance of harnessing the heterosis of catfish, particularly the Pelteobagrus and Bagridae species. Consequently, this review provides an update on the current available information regarding the seed industry of the Bagridae fish family. Full article

As an important freshwater species with economic and ecological benefits, silver carp (Hypophthalmichthys molitrix) exhibits poor tolerance to hypoxia. Glucose transporters (GLUTs) are core membrane proteins that transport glucose to tissues and regulate essential life activities. Its expression is regulated by HIF-1α and cells in hypoxic conditions to maintain energy demand through GLUTs inducing enhanced glucose transport. We cloned H. molitrix glut1 (SLC2A1) and analyzed its sequence using bioinformatics tools. The glut1 cDNA was 2104 base pairs long and encoded a 490 amino acid protein. Phylogenetic analysis revealed that sliver carp glut1 is evolutionarily conserved and exhibited the highest sequence similarity with Ctenopharyngodon idella glut1. Glut1 expression was the highest and lowest in the gills and liver, respectively. Hypoxic stress significantly increased glut1 expression in the brain (p < 0.05); in the gills, it was the highest and lowest in the semi-asphyxia and asphyxia groups, respectively; in the liver, it was significantly higher under hypoxia than that of the normoxia group; and in the heart, it was significantly higher in the floating head, semi-asphyxia, and asphyxia groups than in the normoxia group (p < 0.05). The proposed mechanism may thus provide the basis for elucidating the molecular basis of silver carp’s hypoxia stress response mediated by glut1. Full article

Smoking represents one of the oldest thermic processing methods of fish, and it was originally used to preserve fish for later meals, delaying spoiling. The objective of this study was to analyze the physicochemical and microbiological safety and quality of two traditionally smoked trout species (Oncorhynchus mykiss and Salvelinus fontinalis). We analyzed the effect of trout processed by traditional smoking, characterizing the samples according to the relationships existing between classical microbial analysis, physicochemical parameters, and the content of polycyclic aromatic hydrocarbons (PAHs). The microbial activity of the smoked fish was very low. Although traditional smoking implies high temperatures and direct exposure to the smoke, Benzo[a]pyrene, Benzo[b]fluoranthene, Benzo[k]fluoranthene, Dibenzo[a,h]anthracene, Benzo[g,h,i]perylene, and Indeno [1,2,3-cd]pyrene compounds had undetectable levels in the samples. The products obtained in this study did not exceed the maximum values imposed by EU legislation regarding the TVB-N values during the 30 days of the experiment. We conclude that traditionally smoked trout has many advantages in terms of quality and safety of the products. Thus, the obtained products are safe for consumption for at least 30 days after processing. Full article

Fish meal (FM) constitutes the main, expensive component in aquatic diets. However, the supply of FM is no longer sufficient to sustain global aquaculture production. This study had the primary goal of assessing if the replacement of FM with enzymatic soybean meal (ESBM) can affect the performance of growth and immunological response in juvenile Gibel carp. Juvenile fish with an initial weight of 45.02 ± 0.03 g were arbitrarily assigned to 18 fish cages of 1 m³ each, then fed with diets of different levels of ESBM (0% (control group), 4%, 8%, 12%, 16%, and 20%) for 159 days. These diets corresponded, respectively, to the replacement levels of 0% (control group), 20%, 40%, 60%, 80%, and 100% FM by ESBM. For the parameters of growth and whole-body composition, no obvious differences were found between the control group and other replacement levels (p > 0.05). Similarly, none of the replacement levels showed significant effects for alanine transaminase (ALT), total cholesterol (TC), alkaline phosphatase (ALP), and glucose (GLU) levels (p > 0.05). Malondialdehyde (MDA) levels, as well as the activities of superoxide dismutase (SOD) and total antioxidant capacity (T-AOC) in plasma, were not significantly affected at all replacement levels, according to the findings of this study (p > 0.05). The replacement level of 60% significantly increased the activities of catalase (CAT), whereas the replacement levels of 20% and 100% markedly decreased the activities of this enzyme (p ˂ 0.05). Hepatic and intestinal tissues in this study did not show obvious alterations at all levels of replacement. Full article

Aquaponics (AP) and biofloc technology (BFT) systems rely heavily on bacterial communities to break down organic matter and cycle nutrients that are essential for fish and plant growth. The functional roles of bacterial communities in aquaculture systems are critical to their sustainable operation. Currently, the research on the combination of BFT and AP systems called FLOCponics (FP) is lacking, thereby hindering our ability to optimize their performance. Here, several characteristics (productivity of fish and crops, physicochemical properties of water, and bacterial community) in FP systems cultivating Japanese eel (Anguilla japonica) and leaf lettuce Caipira (Lactuca sativa) were compared to those in the BFT system. Additionally, the effect of fish density on the FP system was investigated. The results indicated that the FP system was more productive than the BFT system. Fish growth rate was highest in the FP system (52.6%), and the average body weight of eels was 168.2 ± 26.8 g in the FP system compared to 140.3 ± 27.0 g in the control (BFT, 5 kg/m²). However, increasing fish density resulted in lower growth rates, with a growth rate of 20.6% observed in the high-density (20 kg/m²) experimental group. The bacterial composition was also significantly different between the systems and fish densities, suggesting that bacterial communities may be closely related to the performance of the aquaponics system. Full article

The fatty acid accumulation in fish tissues are closely related to fish sex, yet the sex differences in fish fatty acids have not been fully known. This experiment investigated the sex differences in fatty acid composition of Chinese tongue sole (Cynoglossus semilaevis), which have typical sexual dimorphism and reversal. Three sexes, namely females, males and pseudomales, were involved in this study. Five batches of fish samples were collected from different fish farms in Shandong Province, China. These fish were identified to be at the gonadal development stage of III–IV. The disparity of fatty acid between sexes (female vs male and pseudomale vs. male) was evaluated by the distance coefficient (D_sex) and multi-variate similarity of percentages analysis (SIMPER). The highest D_sex values between females and males were found in gonad, followed by liver and eye. The fatty acids that differed between females and males were mainly DHA, 16:1n-7, 18:1n-9, and 18:0. The sex difference in DHA and 18:1n-9 contributed significantly to the overall sex difference in fatty acid of brain, eye, and gonad, whereas that in 16:1n-7 contributed significantly in heart, gill, liver, and muscle. The sex difference in 18:0 contributed significantly to the overall sex difference in fatty acid of heart, gill, gut, and skin. The sex differences in fatty acid between pseudomales and males were generally insignificant. In conclusion, at this gonadal development stage (III–IV), the sex differences in fatty acid between female and male Chinese tongue sole have emerged, mainly in the gonad. The testes had higher DHA levels but lower levels of 16:1n-7 and 18:1n-9 than ovaries. In addition, for pseudomales, the phenotypic sex more substantially determined the fatty acid composition than the genetic sex. Full article

Mugil cephalus is an estuarine species that has been shown to acclimate to a diversity of environmental conditions being a good candidate to diversify aquaculture. The objective of this study was to evaluate the growth and water quality of M. cephalus juveniles in a biofloc technology system (BFT). Over a period of 87 days, mullet juveniles (117.36 ± 6.48 g) were reared in two experimental conditions: water exchange (control group) (50% three times a week) and BFT (C:N ratio of 15:1). M. cephalus juveniles were stocked at a density of 7.2 kg·m⁻³. Water quality parameters were monitored periodically. Fish were fed with a balanced artificial feed for marine fish (2% of the total biomass). The water quality parameters were similar between the treatments, with the exception of pH, alkalinity, TSS, and N-NO₃ (p < 0.05). Zootechnical parameters WG, DWG, BG, SGR, condition factor, and survival did not show significant differences (p > 0.05). The biomass gain was higher in BFT (p < 0.05). Water quality variables did not appear to influence mullet survival under culture conditions. Mullet is a species that can be reared in BFT without compromising productive performance and having a significant saving of water. Full article

Porphyra yezoensis polysaccharides (PPs) have biological activities such as promoting digestion, functioning as antioxidants, and improving intestinal health. The aim of this study was to investigate the effects of PPs on the intestinal health of spotted sea bass (Lateolabrax maculatus). A total of 360 spotted sea bass (10.53 ± 0.02 g) were randomly divided into six groups. Fish in each group were fed with varying PP concentrations (0, 3, 6, 9, 12, 15 g/kg) for 52 days. The results showed that 12 g/kg PPs significantly increased the body weight gain, specific growth rate, and condition factor, while there was no significant change in the feed conversion ratio. A supplementation dosage of 9 g/kg PPs significantly increased intestinal amylase activity, and 12 g/kg PPs supplementation significantly increased intestinal trypsin activity. In addition, compared with the control group, there was no difference in lipase in the experimental groups. When fed 9 g/kg, the intestinal glutathione content was significantly increased, and the malondialdehyde content was significantly decreased; the effect of PPs on the catalase activity was not significant. PPs improved intestinal morphology, specifically by improving the intestinal villus morphology and increasing the intestinal lining surface area. Compared with the control group, PPs increased the abundance of Firmicutes and Bacteroides. At the genus level, Cyanobacteria, Muribaculaceae, and Lachnospiraceae were the main flora in the intestinal tract of spotted sea bass. In addition, PPs increased ACE and Chao1 indices of the intestinal microorganisms, while the Simpson index and Shannon index did not change significantly, indicating that intestinal microbial composition and abundance had increased to a certain extent. The results indicated that different levels of PPs in feed can improve the intestinal physiological and biochemical indexes, intestinal morphology, and microbial composition, and thus improve the intestinal health of spotted sea bass. Full article

The aim of this research was to evaluate the health status of the Scophthalmus maeoticus (Pallas, 1814) population from the Romanian marine area in 2016–2019, by identifying and investigating information about bacterial and constitutional diseases, establishing the influence of these bacterioses on the researched populations, and highlighting the main biological disorders (reproduction, growth, and feeding) that manifested in the analyzed fish. The bacterial diseases reported in S. maeoticus (Pallas, 1814) populations were caused by pathogens from the genera Vibrio, Aeromonas, and Pseudomonas. Numerous skin diseases, especially various types of “wounds”, lesions of bony tubercles, and tissue lesions may be the subsequent cause of neoplasms, as a result of fishing gear manipulations. The appearance of significant changes in the prevalence of neoplasia on the Romanian Black Sea coast can be considered an indicator of chronic stress (anthropogenic impact), rather than acute (environmental impact), and we suggest that the species could be used as a biological indicator of changes that may occur in the habitat in which it lives. In terms of future research directions, a combined analysis of the population structure, morphology and diseases determined in S. maeoticus populations, with a structural analysis of the habitat and bacteria contamination degree would be useful; this monitoring should be carried out regularly, to reveal changes in the Black Sea ecosystem, and to propose possible recommendations and protective measures. Full article

The potential of polychaetes for the bioremediation of aquaculture sludge gained more attention in recent years. These organisms can reduce organic matter and nutrients contained in the sludge of several aquaculture species, improving the sustainability of these activities. The aim of this study was to evaluate the removal performance of Perinereis gualpensis (Jeldes, 1963) being fed with aquaculture sludge produced by a recirculating system cultivating Atlantic salmon. The experiment involved adding different amounts of sludge (10% and 20% with respect to total substrate) at a density of 300 organisms m⁻² during 30 days. A treatment without sludge served as a control, using natural substrate. The highest removal rate of total organic matter (TOM) (23.95 ± 13.19 g m⁻² day⁻¹) was achieved by P. gualpensis with 20% sludge addition, a reduction of about 36% compared to the total amount added at the beginning of the trials. The organisms fed with aquaculture sludge presented higher nitrogen (8–9%) and carbon (40–43%) contents, with a maximum organic carbon assimilation of 32% in relation to the total content in the sludge. The high survival (88–95%) and positive growth rates (0.28% day⁻¹) achieved by P. gualpensis indicated that this species can be sustained with salmon sludge as the only source of food. These results indicate that P. gualpensis is a promising candidate for removing nutrients from salmon effluents. Moreover, the protein contents achieved by the organisms (52–58%) meet the dietary protein requirements of several aquaculture species. Further research is needed to determine the maximum bioremediation capacity of this species and to evaluate the lipid content and fatty acid profiles of P. gualpensis to determine its potential application in aquaculture feed. Full article

Suppressor of cytokine signaling (SOCS) genes are essential negative regulators that modulate cytokine signaling and play key roles in numerous biological processes, including immune responses. In this study, we cloned the complementary DNA (cDNA) sequences of two SOCS genes, designated as LvSOCS6 and LvSOCS7, from the whiteleg shrimp, Litopenaeus vannamei. LvSOCS6 encoded a polypeptide of 463 amino acids (aas), spanning 1392 base pairs (bps), while LvSOCS7 encoded a significantly larger polypeptide of 955 aas, encompassing 2868 bps. Both LvSOCS proteins exhibited conserved domains associated with SOCS, including a centralized Src homology 2 (SH2) domain and a C-terminal SOCS box. Phylogenetic analysis revealed that the deduced aa sequences of LvSOCS6 and LvSOCS7 clustered within the invertebrate type I SOCS family, indicating their evolutionary relatedness. Tissue distribution analysis demonstrated ubiquitous expression of both LvSOCS genes across all examined tissues, with LvSOCS6 showing heightened expression in the gills and LvSOCS7 in the gills and stomach. Notably, mRNA expression patterns of LvSOCS genes following LPS and poly (I:C) stimulations exhibited significant upregulations, while PGN stimulation yielded incongruous results across the examined tissues. Interestingly, concurrent with the diminished expression of LvSOCS6 and LvSOCS7, there was significant elevation in mRNA expression levels of LvSTAT, a vital component of the Janus kinase (JAK)/signal transducer and activator of transcription (STAT) pathway. These findings shed light on the potential involvement of the newly discovered type I SOCS genes in regulating the JAK/STAT pathways and playing pivotal roles in orchestrating the innate immune responses in L. vannamei defense mechanisms. Full article

Girella punctata and Girella leonina are economically important species found in the East Sea; along the southern coast of Korea; south of Hokkaido, Japan; around Taiwan; and in the East China sea. In Korea, these two species hold high value, particularly on Jeju Island. These species have similar appearances, and it is challenging to distinguish them, particularly during the seed period. We detected genetic differences in the mtDNA (COI gene) of G. punctata and G. leonina, which are morphologically indistinguishable, and developed species-specific genetic markers for their identification. In total, 16 and 4 haplotypes of the COI genes were obtained from G. punctata (n = 164) and G. leonina (n = 36), respectively. The haplotype diversity (Hd) and nucleotide diversity (Pi, %) of the COI were 0.359 and 0.054 for G. punctata and 0.560 and 0.078 for G. leonina, respectively. We designed a Girella species common primer (control) and species-specific primer sets (experimental) for the two species. Amplicon sizes of 991, 579, and 391 bp were obtained for common primers of the two Girella species G. punctata and G. leonina. To confirm multiple targets in a single reaction, multiplex PCR conditions were optimized to adjust its resolution and accuracy. The detection levels of the multiplex PCR were confirmed to be 0.01 ng/µL for the two Girella species. The multiplex PCR was not associated with cross-reactivity between G. punctata and G. leonina. This multiplex species-specific PCR method provides a simple and rapid technique for the identification of two Girella species, thus increasing the efficiency and quality of Girella species stock management and forensic identification to prevent species misidentification. Full article

Welfare assessment currently is less well-characterized for aquatic animals and the classical methodologies used for terrestrial animals are not adequate to improve our knowledge about fish well-being. Among different approaches, the status of organism responses can be carried out using different physiological and biochemical tools. Here, we present the state of the art regarding fish welfare, methodologies, and experimental results with a particular focus on two important Mediterranean aquaculture species, Sparus aurata and Dicentrarchus labrax. We introduce an approach using physiological stress-indicators, growth performance and swimming activity to investigate the effects of the implantation of electronic tags to facilitate the application of telemetry for aquaculture purposes. The application of telemetry to research on aquatic organisms has expanded recently, and its utilization needs to be better understood. The mentioned approaches have been discussed for application in different aquaculture methodologies. Moreover, social stress and territoriality are relevant factors in the evaluation of gregarious species that may have consequences on the conditions of animals farmed in captivity. These aspects, that may impair the ability of fish to respond to various stimuli or negatively influence the flesh quality, here are analysed through behavioural observation, flanked by the physiological and immunological approach. Full article

This study was conducted to evaluate the oligomeric proanthocyanidins (OPC) in alleviating the detrimental effects of intestinal health caused by dietary histamine in juvenile American eels (Anguilla rostrata). A total of 480 fish with a similar body weight of 10.84 ± 0.16 g were randomly divided into four groups, and there were the control group fed a basal diet, the HIS group fed a diet with a high level of histamine (534 mg/kg), the H + OPC I group fed the high histamine diet with 300 mg/kg OPC, and the H + OPC II group fed the high histamine diet with 600 mg/kg OPC, respectiviely. After the fish were fed the trial diets for 77 days, the intestinal samples were taken, and the related parameters of intestinal health were analyzed. Dietary 300 mg/kg or 600 mg/kg OPC could reverse the decreased activities of lipase, protease, and glutathione peroxidase and the level of total antioxidant capacity, the increased intestinal malondialdehyde and D-lactate acid levels and the activity of diamine oxidase in serum, and the decreased villus height caused by a high level of dietary histamine. There were no significant differences above all the indices between the H + OPC I group and the H + OPC II group. The higher relative abundances of potentially pathogenic bacteria were induced by the high level of dietary histamine. Dietary 300 mg/kg OPC might increase the relative abundance of the potential probiotics and inhibit the colonization of intestinal pathogenic bacteria of juvenile American eels exposed to the stress of high dietary hisatamine. The intestinal health status of the H + OPC groups was similar to that of the control group. These results suggested that dietary 300 mg/kg OPC might alleviate the detrimental effects of dietary 534 mg/kg histamine on the intestine health of juvenile American eels by increasing the activity of digestive enzymes, improving the antioxidative potential and barrier function, and beneficially modulating the intestinal microbiota. Dietary 600 mg/kg OPC could not exert further improvement in growth performance and the intestinal health of juvenile American eels. Full article

The lack of data on the age, growth, and reproduction of the Atlantic Goliath Grouper Epinephelus itajara off the coasts of Florida (USA) makes it difficult to estimate the extent of their population recovery following the 1990 fishery closure, as well as the potential effects of the recent (2023) opening of a fishery for juveniles. Goliath Grouper from the Atlantic coast of Florida were non-lethally sampled for size (total length, TL), age (via fin rays), and sex and reproductive stage (via gonad biopsies, milt/egg expression, gonopores) from May to October 2010–2016. Of 653 unique fish captured (not including 118 recaptures), 257 (39.4%) were females (122–228 cm TL; 5–20 years old), 264 (40.0%) were males (104–225 cm TL; 4–22 years old), 100 (15.3%) were unsexed (82–211 cm TL; 3–15 years old), and 32 (4.9%) were protogynous hermaphrodites (108–209 cm TL; 5–20 years old). Protogyny was conclusively determined in two fish recaptured and re-biopsied that had transitioned from female to male. However, an overlap in the age and size of males and females, a 1:1 sex ratio, and the presence of relatively small, young, mature males, in combination with an apparently low functional sex change rate, all indicated that the sexual pattern of Goliath Grouper was functionally gonochoristic with the potential for diandric protogyny. Females > 10 years old were larger-at-age than males, and Goliath Grouper from the Atlantic coast were larger-at-age than fish from the Gulf of Mexico. These differences in age, growth, and reproductive strategy—as well as the nascent fishery for juveniles—need to be monitored closely so that the current and future reproductive capacity of the population continues to ensure growth and sustainability. Full article

The highly polymorphic taxon European brown trout (genus Salmo) has high phenotypic plasticity, displaying a complex pattern of morphological and life-history variation, contributing to taxonomic confusion. Three main mitochondrial lineages (Adriatic, Mediterranean, and marmoratus) developed during the Pleistocene climatic events in the southern Alpine ecosystem. Here, the natural distribution of native brown trout S. trutta is controversial, complicated by introductions of the Atlantic strain. By investigating museum vouchers, this study aimed to retrace the historical presence of brown trout in the southern Alpine ecosystem before the beginning of mass introductions, which occurred since the middle of the 19th century. By examining the combination of historical and current genetic variability, this study aims to depict the actual impact of introductions of the introduced strain, increasing knowledge and informing conservation strategies and future management plans. The molecular approaches selected were: (i) sequencing of the mitochondrial control region and (ii) genotyping of the nuclear gene LDH-C1*. Vouchers dated the presence of the native Adriatic strain since 1821, while current genetic variability showed the widespread signature of introgression, a consequence of several decades of introductions. Focused plans to preserve local lineages are urgently needed, including short-term solution to avoid complete pauperization of this ecosystem. Full article

The baseline data pertaining to the population of the East Asian finless porpoise (Neophocaena asiaeorientalis sunameri) in Chinese waters are significantly deficient. Boat-based visual line transect surveys were conducted from 2018 to 2020 to evaluate the distribution and abundance of the East Asian finless porpoise in the coastal waters (depth < 30 m) of the Yellow Sea, with a specific focus on the Shandong Peninsula. A total of 50 transects covering 2705 km were conducted, encompassing an area of 23,604 km² between 119°30′ E–123°15′ E and 35°25′ N–38° N. Throughout the surveys, a total of 117 East Asian finless porpoise groups were detected, with over 90% of these groups occurring within 15 km of the coast or adjacent islands. The estimated abundance of the East Asian finless porpoise in the study area was determined to be 3978 individuals (CV = 22.39%, 95%CI = 2561–6177), reflecting a low density of 0.169 individuals/km² (CV = 22.39%, 95%CI = 0.109–0.262) within the coastal waters of the Yellow Sea in the Shandong Peninsula. The findings highlight the need for conservation measures to address the threats faced by this species, including bycatch, habitat degradation, and pollution. The establishment of marine protected areas and the implementation of bycatch mitigation measures are crucial for the long-term survival of the East Asian finless porpoise population in the study area. By providing valuable data on the distribution and abundance of the East Asian finless porpoise, this study contributes to our understanding of the population dynamics and conservation status of this threatened species in the Yellow Sea of the Shandong Peninsula. Full article

This work aimed to assess the suitability of a microalgal blend as a dietary ingredient for feeding juveniles of marine carnivorous and herbivorous teleost, as is the case of Sparus aurata and Mugil cephalus, respectively, and to isolate microorganisms from different media and characterize them on the base of their enzymatic activities and their antagonism against important fish pathogens. Thirty juveniles of each species (70 ± 3.2 g S. aurata mean weight and 47 ± 2.8 g M. cephalus mean weight) were distributed in four tanks (15 individuals each) corresponding to four independent dietary treatments (control and microalgae diets designed for each species). Fish were fed their corresponding diets ad libitum for 108 days. At the end of the trial, fish were weighed, and plasma, liver, perivisceral fat, and the entire intestines were obtained for the evaluation of growth performance and metabolic assessment. Furthermore, 117 bacterial strains were isolated in different culture media from the gastrointestinal tract of S. aurata fed the microalgae blend and further characterized for their potential use as probiotics in aquaculture. S. aurata fed the microalgae-supplemented diet (25% dietary inclusion) showed a significant increase in weight gain, specific growth rate, feed efficiency, hepatosomatic, and intestine length indices. However, growth performance and somatic indices in M. cephalus were not affected by the experimental diets. Plasma samples from S. aurata fed the microalgal diet revealed higher levels of glucose and triglycerides and a decrease in cortisol levels. No significant differences were found in any biochemical parameters among the experimental diets in M. cephalus. In conclusion, both species demonstrated a favorable adaptation to the nutritional formulation employed in this study, and bacterial strains UMA-169 and UMA-216 (both identified as Bacillus pumilus) could be considered for use in aquaculture as they might benefit host health by improving digestion and absorption of different energy sources and by minimizing the colonization of pathogenic species. Full article

Background: The effects of climate change negatively affect marine bivalves’ health. Lately, the intensity of marine heatwaves poses serious threats to the aquatic environment setting of high-risk bivalve farming. Since temperature increases can jeopardize bivalves’ immunity response, pathogen infection becomes more evident. Reactive oxygen species (ROS) production, increased during the process of phagocytosis, is confronted by the animals’ antioxidant defense system. However, apart from pathogenic infections, antioxidant defense responses are also induced by seawater temperature increases; Methods: To enlighten the antioxidant status of Mytilus galloprovincialis originating from mortality events enhanced by intense heatwaves in Thermaikos Gulf, northern Greece, along with Marteilia refringens infection, we examined the expression of genes related to antioxidant defense (catalase, CuSOD and mt10) along with the lipid peroxidation levels and activity levels of antioxidant enzymes (catalase, SOD and glutathione reductase); Results: Our results exhibited increased levels of all these biomarkers. This increase was intensified in the Marteilia infected individuals; Conclusions: Our findings shed light on the oxidative and antioxidant status of farmed mussels led to mortality in the context of Marteilia infection. The latter is augmented by the synergistic effect of heatwaves causing a significant increase in oxidative damage and subsequent antioxidant defense. Full article

Southern swordtail fishes, which belong to the viviparous teleosts called Xiphophorus, are unique models for studies of evolution of sex chromosomes. Monofactorial sex-determining systems, with either the male or the female being the heterogametic sex, as well as sex determination involving more than two sex chromosomes, are found in swordtails and related species. Some swordtail species seem to have originated by crossing between two closely related species. Although the sword has disappeared in many Xiphophorus species during evolution, females of non-sworded species still prefer sworded males, demonstrating a discrepancy between natural and sexual selection. Natural sex change has not been documented sufficiently convincingly in swordtails, but, at least in some subspecies, two or more male phenotypes exist. In a laboratory experiment performed for over 30 years, it has been observed that sex-determining genes may be translocated from one chromosome to another in hybrids of these evolutionary young species. While the factors suggested to play central roles in sex determination and differentiation, e.g., Dmrt1 and AMH, are highly conserved during evolution, several master determining factors have been detected in teleosts. Endocrine-induced sex reversal has been demonstrated in the guppy Poecilia reticulata, another viviparous fish. In swordtails (X. helleri), endocrine disruptors such as nonylphenol and bisphenol A may cause testis cell degeneration and the inhibition of spermatogenesis. Furthermore, swordtails are very easy to breed in freshwater aquaria and, therefore, may be good models for studying the factors influencing sex determination and male differentiation. Full article

Post-mortem ovarian tissue degradation from handling effects, such as delays in preservation, can lead to inaccurate reproductive assessments. Therefore, it is important to understand the differences between handling effects and natural ovarian atresia. Seven treatments of various holding temperatures and times to preservation were applied to whole fish and extracted ovaries of three tropical deepwater snapper species. Ovarian post-mortem degradation was observed at 12 h at ambient temperature and after 48 h iced or refrigerated for both whole fish and extracted ovaries; however, degradation did not adversely affect correct reproductive phase classification in fishes stored in ice from 12 to 48 h post-capture. A clear histological indicator of post-mortem degradation was the breakdown of ooplasm organelles at the oocyte periphery observed in vitellogenic and cortical alveolar oocytes. However, the chorion typically remains intact during post-mortem degradation, in contrast to natural atresia. Effects on post-ovulatory follicles were most discernible after 96 h on ice or refrigeration. Freezing gonadal tissue resulted in drastic changes to oocyte shape and morphology, making reproductive phase classification challenging. We advise that (1) freezing ovaries should be avoided where possible, and (2) gonad tissue should ideally be preserved immediately but no later than 48 h post-capture. Full article

In fish, the immune system plays a crucial role in defending against pathogen-induced infections. The interleukin 17 (IL-17) family, which is a well-studied class of cytokines, serves as a key component of the immune response against external pathogens. In this research, four IL-17 ligands (IL-17A/F1, IL-17B, IL-17C and IL-17D) and one receptor (IL-17RB) genes were identified from spotted sea bass (Lateolabrax maculatus). Alignment analysis showed that the C-terminal region of IL-17 ligands in spotted sea bass was highly conserved. The expression of the IL-17 ligand and receptor genes differed in unstimulated tissues. To investigate the impact of various factors on the immune response of spotted sea bass, we assessed the effect of lipopolysaccharide (LPS), polyinosinic–polycytidylic acid [poly (I:C)] and Edwardsiella tarda treatment on the IL-17 ligands and receptor responses. Our results reveal that the expression of the IL-17 ligand and receptor transcripts is modulated by LPS, poly (I:C) and E. tarda, indicating their significant role in the immune system. Full article

Soy lecithin (SL) is a source of phospholipids, which play a crucial role in determining cell membrane structure, fluidity, and functionality. This study investigated the effects of dietary SL on the performance, nutrient digestibility, and body composition of Nile tilapia juveniles (average initial weight 12.2 g) raised at 22 °C. The experimental diets contained increasing levels of SL (0.0, 21.0, 43.0, and 64.0 g kg⁻¹). The best weight gain and feed efficiency occurred with 42.2 and 49.8 g kg⁻¹ of SL inclusion, respectively, estimated through quadratic regression after 90 days of feeding. The body composition of the fish was also affected by feeding with SL, with a decrease in total body lipids and viscerosomatic and hepatosomatic indices but an increase in polyunsaturated fatty acids. A digestibility trial using only two diets (0SLD and 43SLD) revealed increased lipid and fatty acids digestibility in fish fed with 43SLD. In addition, the consumption of digestible nutrients was the highest in fish fed the diet 43SL. Therefore, SL supplementation is beneficial in fall/spring diets for Nile tilapia juveniles as it can improve growth, lipid digestibility, and body composition when supplemented within the range of 42 to 50 g kg⁻¹ diet. Full article

Connectivity is critical for stream fish persistence, and fish passage structures are a useful conservation tool to reconnect fragmented systems. The design of fish passage structures is a tradeoff between the area available for construction, slope, and costs associated with the structure. The Longrie–Fecteau fish passage structure was designed to be modular, adjustable to barrier-specific needs, and to have a low slope (2%) to pass small-bodied fishes. We evaluated fish passage through this structure in Fountain Creek, Colorado, USA, via a PIT tag mark–recapture study. We documented four native Great Plains fish species successfully ascending the passage structure, with most passage occurring at night. We estimated a 3% probability of a released fish entering the structure, then 89% and 99% passage to the midpoint and exit of the 123 m structure, respectively. Low entrance efficiency was due to low recapture probability of small-bodied study organisms in a relatively large system, and the low percentage of space of the entryway on this barrier (<3% of the length of the barrier). Fish that entered the structure ascended quickly, with median time for successful ascent of 19 min, and minimum time of 6 min. The Longrie–Fecteau fish passage structure is a conservation tool that may broaden the adoption of fish passage structures for small-bodied fishes due to its modularity and low slope. Full article

The eastern Mediterranean Sea is one of the most invaded marine ecosystems due to the introduction of Lessepsian species, which migrated from the Red Sea to the Mediterranean Sea following the construction of the Suez Canal. Some of these species may initially appear to be beneficial for fisheries by providing additional income sources for fishers; however, this usually occurs at the expense of negatively impacted native species and, thus, the ecosystem, which leads to greater economic losses for the fisheries in the long term. Therefore, this study aims to quantify the impact of N. randalli, which is one of the Lessepsian species with increasing commercial importance for the fisheries, on the food web dynamics in a coastal ecosystem in the northeastern Mediterranean Sea using a mass-balance food web modelling approach by capitalising on field data obtained from trawl samplings conducted within the scope of the study. Results showed that the ecosystem was in a developmental stage and experienced an autotrophic succession. The keystone fish group with a structuring role in the food web was sea breams and porgies. Although N. randalli had positive impacts on certain commercially exploited indigenous demersal fish species by mitigating the negative impact of another Lessepsian species, i.e., Saurida undosquamis (Richardson, 1848), in the food web, it had a negative impact on the keystone group of the food web, i.e., sea breams and porgies. Therefore, N. randalli poses a potential threat to the ecosystem’s structure, and the interactions of N. randalli with other species in the food web may instigate an ecosystem reorganisation in the future. We suggest targeted fisheries exploitation and incentives for the fishery of N. randalli as management strategies to mitigate its negative impacts. However, the mitigating role of N. randalli in regulating the negative impacts of S. undosquamis could be adversely affected by its increasing exploitation; therefore, future modelling studies should consider scenario simulations to test such effects. Full article

In this study, we determined the biological characteristics and indices of abundance and biomass of two demersal species, turbot and thornback ray, through a scientific trawl survey of Bulgarian Black Sea waters in the autumn of 2020. Turbot is among the most valuable fish species in the Black Sea, and thornback ray is a sensitive cartilaginous species with a significantly declining abundance throughout the Mediterranean region. The stock biomass of turbot was estimated at 1467.6 tons, with a relative abundance of 896,922 individuals, and those of the thornback ray were 1187.9 tons and 519,606 individuals, respectively. Mean turbot abundance, interpolated into 0.5° latitude/longitude grid cells, ranged between 52 and 120 ind·km⁻², with a mean biomass of 78.26–238.31 kg·km⁻², and for the thornback ray, these indices were within the limits of 0–107 ind·km⁻² and 0–219 kg·km⁻². The distribution of the different length classes of the two fish species by depth layer was analyzed. Length–weight relationships were estimated based on combined samples of both sexes and separately for female and male individuals, allowing a better understanding of growth patterns. Full article

Despite the global decline in marine species biodiversity, relatively few countries have enacted national endangered and threatened species legislation. Tailoring an adequate legislative framework with clear objectives and regulations consistent with the available scientific evidence is fundamental for the effective conservation of marine endangered and threatened species. This paper analyzes the legal framework and current institutional tools for the conservation of marine endangered and threatened species in the Russian Federation. In this regard, important legislative tools include federal laws, as well as internationally binding signed agreements, among others, such as the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES) and the Convention on Wetlands of International Importance Especially as Waterfowl Habitat (Ramsar). A strategy and an action plan for the conservation of biological diversity were also developed. Besides, the most important tool for the conservation and protection of marine endangered and threatened species is the Red Book of the Russian Federation (RBRF) and other regional Red Books. Responsibility for causing harm to the species listed in the RBRF and their habitat is specified in the code of administrative offenses and the criminal code of the Russian Federation. Finally, conclusions and identified gaps were highlighted in the last section, including, among other things, that legislation is still limited in how it takes the impacts of climate change into account. Such type of study is highly recommended, considering the relatively few number of papers dedicated to the study of the impact and/or implications of the conservation tools and strategies mentioned in this paper on the status of the marine endangered and threatened species. Full article

Atlantic goliath grouper (Epinephelus itajara), the largest reef fish in the Western Atlantic, exhibit high site fidelity to home reefs but also undertake annual migrations to distant spawning sites. Once relatively common throughout Florida and the Caribbean, the species; is now considered vulnerable (i.e., threatened with extinction) due to overfishing and loss of juvenile mangrove habitat. Goliath grouper in the southeastern US form annual spawning aggregations on high-relief reefs located offshore of both the Gulf and Atlantic coasts of Florida, US. To determine spawning site fidelity and describe migration patterns to aggregations, we implanted 50 adult goliath grouper with acoustic transmitter tags from 2010 to 2013. Fish were tagged at known spawning sites off the Florida Atlantic coast and tracked as they moved through the FACT Network array of acoustic receivers. From 2010 to 2020, we collected ~7 million detections from tagged goliath grouper at 153 sites along the southeastern US Atlantic coast. Results of this long-term tracking indicate that adult goliath grouper are relatively sedentary during non-spawning months (Nov to June) but move significantly more prior to, during, and immediately after spawning (July to Oct). Inter-annual spawning site fidelity was high: between 80–93% of tagged fish returned to the same spawning sites each year. Arrival timing at spawning sites coincided with the August new moon, with males arriving earlier than females. Some individuals migrated distances greater than 400-km per year, with observed migration rates of up to 44-km per day prior to spawning. Long-term tagging data are critical for understanding movement patterns and developing management strategies for this species of special conservation concern. Full article

Pseudomonas plecoglossicida is the pathogen of visceral white spot disease in marine fish, which usually occurs at 16–19 °C and has resulted in heavy economic losses. Our previous RNA sequencing revealed that the expression of the fliL gene in P. plecoglossicida was significantly up-regulated during infection of the host. In order to study the influence of the fliL gene on the virulence of P. plecoglossicida, the fliL gene of the NZBD9 strain was knocked out by the homologous recombination method, the fliL gene-deleted strain (ΔfliL strain) constructed, and complemented the fliL gene to the ΔfliL strain to obtain the C-ΔfliL strain. The growth curves of the NZBD9 strain, ΔfliL strain, and C-ΔfliL strain did not show significant differences. Compared with the NZBD9 strain, the motility, adhesion, and biofilm formation ability were tendered in the ΔfliL strain (p < 0.05); the complement of the fliL gene enhanced these abilities to the level of the NZBD9 strain. The results of artificial infection experiments showed that the LD₅₀ of NZBD9 strain, ΔfliL strain, and C-ΔfliL strain in hybrid grouper (Epinephelus fuscoguttatus ♀ × E. lanceolatus ♂) were 5.0 × 10³ CFU/fish, 6.3 × 10⁴ CFU/fish, and 1.3 × 10³ CFU/fish, respectively. RNA sequencing was performed on wild-type strains and ΔfliL strains. A total of 126 differentially expressed genes (DEGs) were screened (p < 0.05), of which 114 were downregulated and 12 were upcontrolled, among which several genes related to the six-type secretion system and transport activity were significantly downregulated. The DEGs were aligned to the GO and KEGG databases and enriched to 44 GO pathways and 39 KEGG pathways, respectively. The active pathways of ABC transporters were significantly enriched in both databases. These results indicate that the fliL gene is related to the movement, biofilm formation, and adhesion ability of P. plecoglossicida, and may reduce virulence by affecting substance transport and bacterial secretion. Full article