Fishes, Volume 7, Issue 5 (October 2022) – 89 articles

Background: The bullet tuna (Auxis rochei) is an epipelagic fish with a worldwide distribution that is highly targeted by fisheries. Genetic diversity and population genetics are good indicators of population structure and thus, essential tools for fisheries management. Knowing which factors (biotic and abiotic) might be shaping such structure is crucial for management plans. In the present study, we assessed the population structure of the bullet tuna in the western and central Mediterranean Sea. Methods: We used two types of genetic data: the mitochondrial DNA control region and seven microsatellite loci. The analysis of 431 sequences with a length of 386 bp from the mtDNA CR and the results from 276 individuals were genotyped by seven microsatellite loci. Results: Both types of markers coincided in showing significant genetic differences between an Iberian Peninsula–Strait of Gibraltar stock in comparison with a North African stock. Conclusions: We argue that this differentiation pattern is likely caused by reproductive strategies such as coastal spawning, larval retention, and natal homing behavior. These results should endorse the implementation of management plans for a resource that currently is not being managed. Thus, to ensure sustainability, these new policies should consider the presence of at least two genetically identified stocks. Full article

Anti-Müllerian hormone (amh), an important regulator of gonad development in male teleosts, regulates the development and differentiation of germ cells. We performed transcriptional knock-down of amh in Nile tilapia (Oreochromis niloticus) using antisense RNA technology, resulting in down-regulation in the expression of amh transcription and Amh protein in males. Compared with the control groups, the fish in treatment groups with down-regulated amh had increased weight and an extremely significant decrease in the gonadosomatic index. Hematoxylin–eosin staining revealed impaired testis development and significant reductions in numbers of sperm. Serum estradiol levels were significantly increased, and the levels of testosterone, luteinizing hormone, and follicle-stimulating hormone were significantly decreased. RNA-sequencing analysis of the fish in the down-regulated amh and control groups identified 12,048 differentially expressed genes, of which 1281 were up-regulated and 10,767 were down-regulated. Kyoto Encyclopedia of Genes and Genomes analysis revealed that differentially expressed genes related to growth and development were mainly enriched in the Cell cycle, Endocytosis, TGF-beta signaling pathway, Wnt signaling pathway, FoxO signaling pathway, Insulin signaling pathway, and MAPK signaling pathway. The RNA-sequencing data accuracy was verified by qRT-PCR analysis of the expression levels of selected differentially expressed genes. The abnormal TGF-beta signaling pathway may cause fish weight gain, testis dysplasia, and abnormal spermatogenesis: smad5, smad3a, tgfb2, tgfbr1b, gsdf, and amh were significantly down-regulated. These findings indicated that antisense RNA technology has strong application prospects and can specifically knock down amh in Nile tilapia, resulting in an abnormal TGF-beta signaling pathway, inhibiting testis development and inducing weight gain. Full article

The omul, Coregonus migratorius (Georgi, 1775), an endemic fish of Lake Baikal, is the main commercial species of essential economic importance for the extensive region of Eastern Siberia. Despite the continuous 250-year study of Baikal omul and intensive commercial fishing, neither fishers nor biologists have ever mentioned or found external annelid parasites in numerous omul catches. Targeted parasitological studies have also never detected these ectoparasites on the body of this fish. In this study, we present the first reliable information on the existence of specific annelid parasites infecting the pelagic population of Baikal omul and report a 4% infestation of spawners in the Selenga River, the largest tributary of Lake Baikal. We also obtained the main morphometric parameters of the infected fishes, the morphology of the unknown parasite and its feeding strategy. DNA-based analysis was applied to ascertain the taxonomy of the leeches and revealed no closely related taxa existing in international genetic databases (e.g., GenBank) to date. A maximum genetic identity of 89–91% was detected with European Caspiobdella fadejewi. The genetic distances in 9–11% of the substitutions from the closest relatives were very high for a reliable molecular identification of a taxon. The Selenga omul leech may represent a potentially new species and genus. Full article

PIWI-interacting RNAs (piRNAs) are an emerging class of small RNAs which protect the animal germline genome against deleterious transposable elements. Nevertheless, the characteristics and sex-related expression patterns of piRNA in Collichthys lucidus remain unknown. In this study, we first performed systematic next-generation high-throughput sequencing in C. lucidus ovaries and testes. We identified 3,027,834 piRNAs across six gonad libraries. Of these, 2225 piRNAs were differently expressed between testes and ovaries; 1195 were upregulated and 1030 downregulated in the testes. Interestingly, the potential target genes of 208 differentially expressed piRNAs had sex-related functions, including germ cell development, gonad development, ovarian follicle development, gamete generation, spermatid development, and spermatogenesis. Moreover, these target genes are involved in the TGF-β, Wnt, MAPK, mTOR, VEGF, and PI3K-Akt pathways. Further, 10 piRNAs were derived from Nectin2 and Mea1, which play important roles in sexual reproduction, male gamete generation, and germ cell development. We also identified 5482 piRNA clusters across the gonads, among which 139 piRNA clusters were uniquely expressed in the testes and 98 in the ovaries. The expression of core sex-related piRNA was validated by real-time PCR. Overall, our findings provide significant insights into C. lucidus’ sex-related piRNAs. Full article

Color preference testing for animals is a prerequisite for optimizing facilities and ensuring animal welfare in aquaculture. Swimming crabs (Portunus trituberculatus) are aggressive, and shelters are often installed in ponds to reduce the high mortality rate caused by their agonistic behavior. To test the preference of juvenile crabs for the color of shelters, this study observes the preferences of crabs for shelters of different colors (white, yellow, blue, and black). The counts and duration of crabs occupying different colored shelters were quantified. The probability of fighting and the probability of abandoning the shelter were also calculated. The results revealed that: (i) when all colors were presented simultaneously, the z-scores of the blue shelters were far higher than others during the day; (ii) when only one color was present, crabs occupied the blue shelter significantly more often and for longer periods of time than others during the day, with invasive crabs exacerbating this preference; and (iii) the probability of fighting between crabs was relatively low in the presence of the blue shelter, and the probability of abandoning the shelter was significantly lower than that of others. Based on these results, blue shelters are recommended for use in swimming crab ponds. Full article

The neon flying squid (Ommastrephes bartramii) plays an important ecological role in the North Pacific. An analysis of stable isotopes in eye lenses was conducted to investigate the inter- and intravariation of the trophic ecology of stocks at the eastern and western North Pacific throughout the life cycle. ${\mathsf{\delta }}^{13}\mathrm{C}$ and ${\mathsf{\delta }}^{15}\mathrm{N}$ values gradually increased with ontogenetic growth of the squid, which was associated with geographic migrations and increased the trophic level. For both stocks, from the paralarval to the juvenile stage, the trophic niche breadth increased, which might be the reason that the swimming and feeding ability improved as they entered the juvenile stage. Meanwhile, interactions between different ecosystems led to a greater diversity of food sources; thus, their feeding targets were no longer limited to plankton but shifted toward small fish and other cephalopods. Then, from the juvenile to the subadult–adult stage, the trophic niche breadth decreased, which can be explained by that O. bartramii had a selective preference for certain prey as ontogenetic growth proceeded, and they seemed to focus more on larger prey in the subadult–adult stage. Furthermore, the small amount of overlap between early and later life cycles suggested a significant trophic niche separation among different trophic ecologies and spatial ecologies. This study provides an understanding of diet shifts in neon flying squid in the North Pacific Ocean, primarily including diet shifts during their individual development and differences in trophic variation between the two stocks. Full article

White tail disease (WTD) is caused by the Macrobrachium rosenbergii nodavirus (MrNV) and an extra-small virus (XSV). MrNV belongs to the Nodaviridae family. While the role of XSV in the pathogenicity of WTD remains unclear, MrNV is considered to be a significant factor in the disease. To study WTD infection in giant freshwater prawns (Macrobrachium rosenbergii), adult and post-larval (PL) prawns were collected from three giant freshwater prawn farms in Gyeongsangnam-do, Korea in 2021. Although the adult and PL prawns did not display any gross signs of WTD, MrNV was detected in both adult and PL in this study. However, XSV was not detected in both prawns. Phylogenetic analysis revealed that the capsid protein gene sequences of MrNV obtained in this study were robustly clustered with the MrNV group, and were clearly distinguished from Alphanodavirus and Betanodavirus groups of the family Nodaviridae. Although Zenker’s necrosis and myolysis were observed histopathologically in the abdominal striated muscle of adult and PL prawns, no gross signs associated with white tail were observed because of local lesions. Full article

Fishing of the brown shrimp Penaeus aztecus is an important socioeconomic activity, generating income and different jobs for the fishing sector; however, this species is exposed to contaminants such as toxic metals. The objective of this research was to determine the concentrations of Cd, Pb, Cr, and Ni in brown shrimp P. aztecus from the northwestern Gulf of Mexico, and to analyse morphometric measurements in this species. The determination of toxic metals in shrimp was carried out according to the method proposed by the USEPA. Sexual identification was carried out by examining the first pleopods of P. aztecus specimens; the stages of maturity and proportion of sexes were also determined, finding specimens at maturity stages I and II. Specimens collected in the Veracruz area presented higher morphometric values, with an average TL of 136.15 mm. It was identified in the same area that the batches were formed by a higher proportion of males at 72.2%. Ni was the metal with the highest concentration in the Veracruz area at 15.5 µg g⁻¹, while Pb had a maximum concentration of 8.3 µg g⁻¹. The concentrations obtained for the toxic metals in the shrimp exceeded the values of the international permissible limits established for Pb and Cd. Full article

Schizothorax kozlovi, as an endemic and vulnerable fish of the upper Yangtze River in China, faces many threats. In order to expose the population structure of wild S. kozlovi, the carbon and oxygen isotopic ratios in the otoliths, and the gene sequences of two common mitochondrial markers (Cytb and COI) were investigated in four sampling locations, and then their relationship with ambient temperature was further investigated. In general, it exhibits limited geographic population structuring of S. kozlovi in the upper Yangtze River by both mtDNA and stable isotopes. The values of otolith stable isotope ratios varied from −15.30‰ to −12.37‰ for δ¹⁸O and from −10.10‰ to −6.13‰ for δ¹³C. Significant relationships were revealed between stable isotope ratios and specific mean monthly water temperature variables (from November to March), indicating low temperature effect on otolith stable isotope ratios. Haplotype diversity and nucleotide diversity were 0.928 and 0.00778, both exhibiting high levels. A median-joining haplotype network indicated a mixture of geographical distribution but exhibited two distinct haplotype lineages (Clade I and Clade II). AMOVA detected that the higher percentage of genetic variance was within sampling locations (96.94%) and between two haplotype lineages (72.82%). Most F_ST values between sampling locations showed small levels of genetic differentiation except the differentiation between population SJ (Sanjiangkou) and JP (Jinping). Therefore, two haplotype lineages and population JP of S. kozlovi in the upper Yangtze River are suggested as three management units for conservation due to their moderate-to-great genetic differentiation and isolated habitat. Full article

To assess the lipid requirements of O. macrolepis broodstock, five iso-nitrogenous diets (39 g kg⁻¹) with five lipid levels, 50 (5 L), 70 (7 L), 90 (9 L),110 (11 L), and 130 (13 L; g kg⁻¹), were made. A total of 105 three-year-old individuals (50.11 ± 2.86 g per fish) were divided into five groups (triplicate per group) and were fed with the diets, respectively, for eight weeks. Then, the fish were sampled, and items were determined. The results showed that growth rate and feed efficiency ratio were not significantly affected by diets (p > 0.05). A clear dose–response effect of dietary lipid was observed on somatic indexes of gonad indexes of the O. macrolepis brookstock, with the highest values corresponding to fish fed 9 and 11 g kg⁻¹ lipids, in contrast, gonad indexes were reduced as dietary lipid moved away from this level. The other somatic indexes, such as viscerosomatic index, perivisceral fat index, etc., were not significantly affected by diets (p > 0.05). The content of crude lipid and crude protein in carcass, hepatopancreas, and gonad were not significantly affected by dietary lipid levels (p > 0.05). The gonad fatty acids of 16:0 and 22:6n-3 decreased and 18:2n-6 increased with the increasing lipid level, being significantly altered by diets (p < 0.05). The histological features of the gonad showed no significant difference among the five diets (p > 0.05). The relative expression of sex steroid-synthesizing proteins (fshr, 3β-hsd, 17β-hsd, aro., and star.) in the gonad of fish was most significantly highly expressed in the 9 L and 11 L groups (p < 0.05). The results suggested that a proper dietary lipid level of 90–110 g kg⁻¹ could maintain gonad development of O. macrolepis broodstock without affecting growth performance. Full article

Clams, Meretrix meretrix, were one of the favorite aquatic products in Taiwan and the world. It was reported that the water pollutants such as heavy metals and chemicals might accumulate in the clam body and shell through filter-feeding behavior. Thus, the bivalves could be used as bioindicators in the aquatic environment. The present study analyzed 20 trace elements, Mg, Sr, Li, Cd, Ba, Mn, Al, U, Ti, Pb, Nd, B, S, Zn, Fe, P, Na, K, Cu, and Ni, in the shells of the clams collected from the wild coastal area and cultured ponds to evaluate which elements have the potential to be biomarkers. The concentrations of 20 elements were detected by Solution-Based Inductively Coupled Plasma Mass Spectrometry (SB-ICPMS). Among them, Cd, Al, U, Ti, Nd, S, and K were below the detection limit. The remaining elements were analyzed for accumulation. The levels of Zn, Fe, and Ni possess high variation in an identical environment; so, a PCA was conducted without these three elements to reduce noise. The PCA result proved that the clam could absorb specific trace elements from the habitat. After a period of time, the contents of the absorption in the shells of the clams living in an identical environment became more similar. The analyzed element, Pb, was not found with a special difference in this study. The levels of Na, Sr, Mg, B, Mn, P, Ba, Li, and Cu reflected different sampling sites, which suggested that these elements in the species M. meretrix had the potential to be used as biomarkers for assessing heavy metal accumulation in the environment. Full article

Coastal homestead ponds are flooded during the rainy season and only hold water for five to six months. For coastal rural people, these ponds have a substantial impact on household nutrition and income generation. However, choosing the right culture techniques, stocking density, and seed size are necessary for fish aquaculture to be effective in this sort of seasonal pond. Hence, an adaptive field experiment was conducted to reveal the growth performance, yield and cost–benefit using advanced carp fingerling at different stocking densities in homestead ponds. Advanced fingerlings of Gibelion catla, Labeo rohita, Cirrhinus cirrhosus, and Labeo calbasu with the mean individual stocking weight of 243 ± 1.87 g, 223.56 ± 2.35 g, 155.89 ± 1.69 g, and 158.72 ± 1.35 g, respectively, were stocked at three different stocking densities, e.g., 825 kg ha⁻¹ in T1, 560 kg ha⁻¹ in T2 and 370 kg ha⁻¹ in T3 and reared for 5 months. Homemade supplementary feed with protein content of 24.25% was supplied twice daily. The specific growth rate (SGR) was recorded highest at T3 for all the cultured species as L. rohita (1.15 ± 0.01% day⁻¹), followed by G. catla (1.12 ± 0.004% day⁻¹), L. calbasu (1.09 ± 0.01% day⁻¹), and C. cirrhosus (0.98 ± 0.002% day⁻¹), respectively. An inverse relationship was detected between fish growth and stocking density for all treatments. A similar pattern was observed in the survival rate, where reduced survival rates were recorded at T1 for all species. Significant variation (p < 0.05) was found among the treatments in terms of final weight, SGR, and survival rate. Economics of the carp polyculture also showed the highest net benefit (2609.77 ± 2.02 USD ha⁻¹) and benefit–cost ratio (2.06 ± 0.002) at T3. Rearing of fish at 370 kg ha⁻¹ stocking density yielded 129.21% and 110.96% higher production in T3 than T1 and T2, respectively. Overall, T3 treatment was more appropriate than T1 and T2 due to its low FCR, low investment but high survival rate, and net return. Therefore, stocking homestead ponds with advanced carp fingerling with a density of 370 kg per ha can be suggested as for increasing fish production and benefit in the homestead ponds of coastal rural area. In addition, further research is recommended to find out the effects of feeding and sources of seeds on the production performances. Full article

Illegal, unreported and unregulated (IUU) fishing is recognised as one of the largest threats to the sustainability of the world’s fisheries. The fight against IUU fishing activities has recently become a high priority in the international fisheries management agenda. While a number of academic contributions have sought to improve the understanding of the problem, data are still limited, especially in developing countries. In the absence of any information in this regard in Egypt, this contribution is the first attempt to report the available information about cases of Egyptian fishing vessels detained for fishing illegally in neighbouring countries, including the Mediterranean and Red Seas. The highest number of cases was observed in 2015 (7 cases) followed by 2010, 2013, 2016 and 2020 (each with 5 cases). The highest number of detained vessels by far was observed in 2020 (44 vessels) followed by 2015 (19 vessels). Tunisia was the country with the highest number of cases (17 cases) followed by Libya (10 cases), while Somalia detained the highest number of vessels (42 vessels) followed by Libya (22 vessels). The results shed light on the problems that led to this situation, starting with depleted fisheries, a poor monitoring system and a difficult economic situation in the fishing sector. Full article

Acute hepatopancreatic necrosis disease (AHPND) is a bacterial disease caused by Vibrioparahaemolyticus. Currently, various Vibrio strains, including V. campbellii, V. owensii, and V. harveyi, have been reported as causative pathogens. Thus, controlling AHPND to maintain high production in shrimp aquaculture is difficult. We evaluated the antimicrobial activity of five Bacillus strains (B1, B3, B5, B7, and B8)—isolated from seawater in Jeju, South Korea—against 12 Vibrio strains (10 AHPND strains and 2 non-AHPND strains). All tested Bacillus strains inhibited the growth of at least one of the tested Vibrio strains in the dot-spot method. Among them, B1 and B3, the most effective Bacillus strains against the Vibrio strains, particularly against AHPND-causing V. campbellii (Vc_AHPND), were further used in a challenge test. After 48–60 h of Vc_AHPND immersion, a significantly higher survival rate was observed in the B1-treated group (100%) than in the non-Bacillus-treated group (64.3%). Based on the qPCR analysis of AHPND, the cycle threshold values were 31.63 ± 0.2 (B1-treated group) and 38.04 ± 0.58 (B3-treated group), versus 28.70 ± 0.42 in the control group. Genome sequencing and phylogenetic analysis revealed that B1 and B3 were classified as B. velezensis. The 16S rRNA sequences and complete genome sequences of B1 and B3 were deposited in GenBank. Full article

The giant mottled eel, Anguilla marmorata, is at high risk of extinction due to overfishing of glass eels and elvers to provide stock for eel farming. In Vietnam, information on the genetic diversity and population structure of this species, which is necessary for resource management, is limited. In order to address this paucity of information, sequencing of the entire mitochondrial control region (mtDNA) was carried out for 176 individuals collected from central Vietnam. The sequences were investigated using various genetic, phylogenetic and population analyses. A total of 165 distinct haplotypes were identified. The percentage of variation within and among populations was 99.26% and 0.74%, respectively. The fixation index was low (0.007) and not significant (p = 0.096). Therefore, panmixia and a lack of significant population genetic structuring seem likely for A. marmorata in central Vietnam. Most sampled eels were genetically similar to eels found in North Pacific populations (Japan, Taiwan and the Philippines), except for one sample from Quang Tri and two samples from Binh Dinh, which had high values of genetic identity (97% to 99%) with South Pacific populations (Tahiti, Fiji, New Caledonia and Papua New Guinea). Taken together, we suggest that A. marmorata from the North and South Pacific populations co-exist in central Vietnam. Full article

Common carp (Cyprinus carpio) is an economically important fish worldwide, with many of its species bred for consumption. However, there are few reports on the comprehensive comparative analysis of the muscle nutritional quality and stress resistance characteristics of different common carp species. In this study, after 15 months of feeding in the same environment, the nutritional components, serum biochemical indices, liver antioxidant and intestinal digestive enzyme activities, and muscle growth-related gene expression were determined in Songpu mirror carp (SPM; Cyprinus carpio Songpumirror), Heilongjiang wild carp (HLJ; Cyprinus carpio haematopirus), cold-resistant strain of purse red carp (CPR; Cyprinus carpio ‘Red purse cold-resistant’), Songhe carp (SH; Cyprinus carpio ‘Songhe’), and Songpu carp (SP; Cyprinus carpio Songpu). Muscle nutrient composition showed that HLJ had a significantly lower crude fat content and higher docosahexaenoic acid (DHA) + eicosapentaenoic acid (EPA) proportion than the other four common carp species (p < 0.05). The contents of lysine (Lys) and aspargine (Asp) were significantly higher in the CPR than in other species (p < 0.05). Serum biochemical parameters showed that total protein (TP), total cholesterol (T-CHO), triglycerides (TG), and low-density lipoprotein (LDL) were significantly lower in SPM than in the other species (p < 0.05). The results of tissue enzyme activity showed that the activities of superoxide dismutase (SOD) and catalase from Micrococcus lysodeikticus (CAT) in the liver were significantly higher, while the activities of lipase (LPS), trypsin (TRS), and α-amylase (α-AMS) in the intestine were significantly the lower in HLJ than in the other species (p < 0.05). In addition, the relative expression levels of growth hormone (GH), growth hormone receptor (GHR), insulin-like growth factor 1 (IGF1), insulin-like growth factor receptor (IGF1R), and myoblast determination factor (MyoD) in SP and SH were significantly higher than those in the other species, while the relative expression of myostatin (MSTN) in HLJ was significantly higher (p < 0.05). Therefore, there were significant differences in muscle nutritional quality, serum biochemical indices, liver, and intestinal enzyme activities, and muscle growth potential among the five species of common carp. This study could provide a theoretical basis for the germplasm evaluation and variety improvement of common carp. Full article

Farmed lumpfish (Cyclopterus lumpus) are commonly used as cleaner fish in the salmonid aquaculture industry, but a knowledge gap exists with regards to their body density. Filling this knowledge gap is of importance, as the lumpfish has no swim bladder and thus relies on alternative methods for buoyancy, i.e., the body density difference between the fish and its surroundings. The aims of this study were to measure the body density of lumpfish and investigate the correlation between body density and different operational welfare indicators. A total of 138 lumpfish were sampled at five different aquaculture sites situated in the Faroe Islands. Weight in water and air was measured, body density was calculated, and operational welfare was assessed. The average body density of the juvenile lumpfish was 1.030 g mL⁻¹. Fulton’s K, stomach score, and length were negatively correlated to body density, while the hepatosomatic index was positively correlated to body density. Liver colour was correlated to body density, but the groupings were too broad for a final definitive conclusion. The knowledge gained from this study might help the industry improve their understanding of the operational welfare indicators used for lumpfish. Additionally, the knowledge might also help the aquaculture industry improve their husbandry and feeding practices. Full article

Integrating marine shrimp and tilapia has been shown to be a viable alternative in a system based on bioflocs, but there is no consensus on the spatial arrangement of farmed animals. The present study aims to (1) compare the performance of shrimp and fish in high density when subjected to polyculture (species in the same tank) and multitrophic (species in different tanks) arrangements, and (2) effects on water quality, especially on organic matter (biofloc). The experiment was carried out for 30 days, and three treatments with bioflocs were evaluated in triplicate: control: shrimp monoculture, polyculture: shrimp and tilapia in the same tank, and multitrophic: shrimp and tilapia in separate tanks. The results show that the best product configuration is the multitrophic system, where the biological control of bioflocs took place, and the best performance of the Pacific white shrimp L. vannamei and Nile tilapia O. niloticus was obtained. Tilapia, as an organic consumer, was effective in controlling bioflocs. Full article

Water area and waterweed coverage are the key environmental factors for ecological breeding of Eriocheir sinensis in ponds. In order to explore the effects of above two factors on the growth of E. sinensis, three groups of experiments were set up: low coverage small area (C1S1), high coverage small area (C2S1), and high coverage large area (C2S2), and water environmental factors and the growth of E. sinensis were monitored. The results showed that the dissolved oxygen of ponds with different waterweed coverage was significantly different (p < 0.05), and the phosphate in ponds changed significantly from July to October (p < 0.05). The correlation analysis showed that NH₃-N and pH were significantly positively correlated (p < 0.05). At the same time, there was a significant negative correlation between NH₃-N and DO, H₃PO₄ and pH (p < 0.05). Further analysis of the relationship between surface area, waterweed coverage and environmental factors revealed that the surface area and waterweed coverage were closely related to NH₃-N, H₃PO₄ and DO. From July to October, the differences in morphology and weight of E. sinensis in different ponds became more and more significant. In terms of growth rate, C1S1 with a small area and low coverage had a downward trend, while C2S1 and C2S2 were the opposite. In the final stage of the experiment, C2S2 had the highest yield (0.1311 kg/m²), and C1S1 had the lowest yield (0.0600 kg/m²). Then, the ponds with high waterweed coverage and large area can bring better benefits. Full article

Information on age and growth is essential to modern stock assessment and the development of management plans for fish resources. To provide quality otolith-based estimates of growth parameters, this study performed five types of analyses on the two important croakers that were under high fishing pressure in southwestern Taiwan: Pennahia macrocephalus (big-head pennah croaker) and Atrobucca nibe (blackmouth croaker): (1) Estimation of length–weight relationships (LWR) with discussion on the differences with previous studies; (2) validation of the periodicity of ring formation using edge analysis; (3) examination of three age determination methods (integral, quartile and back-calculation methods) and selection of the most appropriate one using a k-fold cross-validation simulation; (4) determination of the representative growth models from four candidate models using a multimodel inference approach; and, (5) compilation of growth parameters for all Pennahia and Atrobucca species published globally for reviewing the clusters of estimates using auximetric plots of logged growth parameters. The study observed that features of samples affected the LWR estimates. Edge analysis supported the growth rings were formed annually, and the cross-validation study supported the quartile method (age was determined as the number of opaque bands on otolith plus the quartile of the width of the marginal translucent band) provided more appropriate estimates of age. The multimodel inference approach suggested the von Bertalanffy growth model as the optimal model for P. macrocephalus and logistic growth model for A. nibe, with asymptotic lengths and relative growth rates of 18.0 cm TL and 0.789 year⁻¹ and 55.21 cm, 0.374 year⁻¹, respectively. Auximetric plots of global estimates showed a downward trend with clusters by species. Growth rates of the two species were higher than in previous studies using the same aging structure (otolith) and from similar locations conducted a decade ago, suggesting a possible effect of increased fishing pressure and the need to establish a management framework. This study adds updated information to the global literature and provides an overview of growth parameters for the two important croakers. Full article

Neon flying squid Ommastrephes bartramii and jumbo flying squid Dosidicus gigas are two important commercial ommastrephid species in the Pacific Ocean. As short-lived marine species, squids are highly susceptible to changes in climate and marine environments. According to samples collected from the northwest and southeast Pacific Ocean in different years, we explored the growth characteristics of these two squids in terms of their mantle length (ML) distribution and the relationship between mantle length and body weight (LWR), also considering the relative condition factors (K_n), and explored the effects of the El Niño and Southern Oscillation (ENSO) on their growth. The results showed that the ML for O. bartramii and D. gigas had significant differences among different years and different sexes (p < 0.01), and the size of females was larger than that of males. LWR showed that both squids demonstrated a positive allometric growth pattern (b > 3), and parameters a and b were influenced by year and sex. Furthermore, there were significant differences in Kn in both squids for different years and different sexes (p < 0.01), and their interannual fluctuations were quite significant. In conclusion, the alterations in the marine environment caused by climate change had a significant impact on the growth of O. bartramii and D. gigas in this study. ENSO events had opposite effects on the growth of both squid species. Full article

The velocity of water can cause differences in the growth of inhabitant fish, thereby functioning as an important aquatic environmental factor. In order to explore the response mechanism of Leopard Coralgrouper (Plectropomus leopardus) under different flow velocities, P. leopardus fish of the same sizes were fed in water characterized by three different flow rates (5 cm/s, 10 cm/s, and 20 cm/s) for 150 d, after which the differences in growth and the levels of liver oxidative stress kinase were analyzed. Additionally, potential underlying regulatory pathways were explored using comparative transcriptomic approaches. The results showed that in the feeding environment involving a flow rate of 10 cm/s, the weight increase of P. leopardus and its liver contents of glutathione peroxidase (GPX), alanine aminotransferase (ALT), and superoxide dismutase (T-SOD) were significantly higher than for the other two groups. After matching the comparative transcriptomic results between group pairs (5 cm/s and 10 cm/s, 5 cm/s and 20 cm/s, and 10 cm/s and 20 cm/s), a total of 225 common differential gene expressions were screened. The KEGG pathway enrichment analysis showed that these genes were mainly involved in protein processing in the endoplasmic reticulum, the TGF-β signaling pathway, fatty acid metabolism, fatty acid synthesis, and other pathways. These results not only provide a theoretical basis for the selection of flow velocity in the culture environment of P. leopardus, but also reveal its potential means of adaption to different flow velocities. Full article

Fish skin mucus is the first line of defense that provides physical and chemical barriers against pathogens and toxins. The mucus is produced continuously and sloughed off regularly from the skin to defend against infections through the skin. However, the molecular properties of the mucus content that prevent pathogen invasion are yet to be fully understood. In this study, a proteomic approach using liquid chromatography–mass spectrometry (LCMS) was applied to explore the changes in the mucus protein content of resistant and susceptible groupers in response to Vibrio alginolyticus. The Vibrio-resistant groupers showed no observable clinical sign of infection after the immersion challenge, while the Vibrio-susceptible groupers presented either hemorrhagic- or non-hemorrhagic ulceration of the skin. A comparative proteome analysis on the mucus samples yielded 1488 identified proteins. The immune-related proteins, namely Cystatin B, Complement Component C6, Complement factor 1, Allograft inflammatory factor 1, Deleted in malignant brain tumors protein, MHC class 1 and Annexin A1, that were significantly abundant in the resistant group responded to V. alginolyticus infection. Interestingly, there was an expression of immune-related proteins that possibly could be the non-invasive biomarkers, namely 3-hydroxybutyrate dehydrogenase type 2 and L-rhamnose-binding lectin SML. Full article

This work determined the feasibility of producing two highly demanded products (cornmeal (CM) snacks and gelatin power) with antioxidant properties and using dry-salted brown cannonball jellyfish umbrella (UM) and oral arms (OAs). Desalted and rehydrated UM and OAs were subjected to drying and milling processes to produce jellyfish flours (UMF and OAF). Five cornmeal snacks were made: 100% CM and ones containing 20% UMF; 50% UMF; 20% OAF; and 50% OAF. Meanwhile, gelatin was obtained from UM and OAs through 0.5 M HCl hydrolysis and thermal and cold maturation treatment. Jellyfish flours increased the protein content of cornmeal snacks. Only OAF improved its antioxidant activity. The addition of 20% OAF did not affect the sensory characteristics of cornmeal snacks. Gelatin from UM had a lower crude protein level, and a gelatin β-component was not observed. Higher hydroxyproline content by HPLC and proton peaks at higher ¹H–NMR fields were observed in OA gelatin. OA gelatin exhibited higher viscosity, foam, and in vitro antioxidant properties. Full article

Japanese sardines (Sardinops melanostictus) are environmentally sensitive pelagic fish. We investigated the effects of environmental factors on the stock-recruitment (S-R) relationship of S. melanostictus in the Pacific Ocean from 1984 to 2018. We modeled and analyzed the recruitment of S. melanostictus using the Ricker model, the Ricker environment extension model (Ricker-E), and the generalized additive model (GAM). Different numbers of environmental factors were added to the models for fitting, and the Akaike information criterion (AIC) was used to select the optimal model. The results showed that the nonlinear GAM provided the best fit. The results of the GAM single factor and multifactor analysis showed that environmental factors were significantly correlated with recruitment in S. melanostictus (p < 0.05). The best fitting model was the GAM, with an AIC of 57.9 and a cumulative explanation rate of 95.7%. Sea surface temperature was the most dominant environmental factor and had a negative impact on R/S. Considering both spawning stock biomass (S) and the environmental factors in the S-R relationship is important for studying the mechanisms of complementary changes and population changes in S. melanostictus under the influence of the marine environment. Full article

Several sampling gears are used to collect fish in the lentic ecosystem. The collected fish differ in their characteristics and community structure depending on the sampling gear. The objectives of this study were to 1) compare the community structure of fish assemblages sampled using four sampling gears (kick net, cast net, gill net, and fyke net) in the Singal (SG), Yedang (YD), and Juam (JA) reservoirs, and 2) to understand the characteristics of fishes collected by each sampling gear. A total of 1887 individuals of 14 species, 9113 individuals of 15 species, and 9294 individuals of 27 species were collected, respectively, from the SG, YD, and JA reservoirs. Among the four sampling gears tested, the fyke net collected the largest numbers of species and individuals, while the gill net collections had the highest diversity index. The results obtained with the self-organizing map (SOM) provided a more detailed characterization of the sampled fish than the metrics that are typically used to evaluate sampling gears. In particular, SOM analysis showed a similar pattern of the standard length of fish and sampling gear. Since each sampling gear has unique characteristics, the selection of an appropriate sampling gear should be based on the study objectives and features of the sampling sites. Full article

European eel is thought to be a symbol of the effects of global change on aquatic biodiversity. The species has persisted for millions of years and faced drastic environmental fluctuations thanks to its phenotypic plasticity. However, the species has recently declined to historically low levels under synergistic human pressures. Sublethal chemical contamination has been shown to alter reproductive capacity, but the impacts and required actions are not fully addressed by conservation plans. This paper proposes a modelling approach to quantify the effects of sublethal contamination by anthropogenic pollutants on the expression of life history traits and related fitness of the critically endangered European eel. Material and Methods: We sampled female silver eels from eight different catchments across Europe previously shown to be representative of the spectrum of environmental variability and contamination. We measured 11 fitness-related life history traits within four main categories: fecundity, adaptability and plasticity, migratory readiness, and spawning potential. We used machine learning in models to explore the phenotypic reaction (expression of these life history traits) according to geographical parameters, parasite burdens (the introduced nematode Anguillicoloides crassus) and anthropogenic contaminants (persistent organic pollutants (POPs) in muscular tissue and trace elements (TEs) in gonads, livers and muscles). Finally, we simulated, the effects of two management scenarios—contamination reduction and contamination increase—on the fecundity and recruitment. Results: Contamination in our sampling was shown to have a stronger control on life history traits than do geographic and environmental factors that are currently described in the literature. We modelled different contamination scenarios to assess the benefit of mitigation: these scenarios suggest that reducing pollutants concentrations to the lowest values that occurred in our sampling design would double the fecundity of eels compared to the current situation. Discussion: Remediation of contamination could represent a viable management option for increasing the resilience of eel populations, with much more effects than solely reducing fishing mortality. More broadly, our work provides an innovative way for quantitative assessment of the reaction norms of species’ biological traits and related fecundity to contamination by organic and inorganic pollutions thus opening new management and conservation pathways to revert the erosion of biodiversity. Full article

This study aimed to investigate the effects of the probiotic Betaplus^® and prebiotic Technomos^® as feed additives for Nile tilapia in terms of growth performance, health profiles, and resistance to infection with Aeromonas hydrophila and Pseudomonas fluorescens. A total of 960 healthy juvenile Nile tilapia (1.5 ± 0.01 g) were randomly divided into four experimental variants with three replicates for each variant. Fish were fed a commercial diet (control group, V₀), supplemented with BetaPlus^® probiotics–1% × BW (V₁), TechnoMos^® prebiotics–1% × BW (V₂), and with BetaPlus^® probiotics and TechnoMos^® prebiotics in a ratio of 1:1% × BW (V₃). Results on growth performance showed the best values in the probiotic variant, correlated with the health profile and the relative survival percentage after the challenge test with A. hydrophila and P. fluorescens. Similarly, the effects of dietary supplementation with probiotics and prebiotics on physiological conditions also recorded beneficial results in the synbiotic variant, where a high survival percentage was obtained after infection with the two pathogenic bacteria. In conclusion, the results of this study indicate that dietary supplementation with feed additives consisting of mentioned probiotics, prebiotic, and their combination as synbiotics has the potential to promote growth performance, improving tilapia immunity and increasing survival after the challenge test. Full article

Antibiotic treatment is regarded as an emergency measure to avoid disease occurrence of aquatic animals during metamorphosis in an aquaculture system, which is very common in hatcheries of bivalve mollusc larvae. However, it is still unclear how and to what extent the antibiotic addition affects the prokaryotic and eukaryotic microbial communities of marine bivalve larvae. We profiled the community compositions and dominant taxonomies of prokaryotic and eukaryotic microbiota of Kumamoto oyster (Crassostrea sikamea) larvae exposed to seawater with antibiotics in trace concentration. A total of 500,664 16S rRNA and 501,933 18S rRNA gene fragments were selected for classification, resulting in 714 prokaryotic Operational Taxonomic Units (OTUs) and 47 eukaryotic OTUs. Antibiotic exposure altered the structure of larval microbiome and increased the prokaryotic but decreased the eukaryotic microbial diversity. Larval microbiota was sensitive to antibiotics, as evidenced by alternation of the dominant bacterial phyla Proteobacteria, Bacteroidetes, Firmicutes, Chlamydiae, and Actinobacteria, and eukaryotic phyla Streptophyta, Cercozoa, Chlorophyta and Haptophyta. Similarly, a significant effect was observed at the family and genus level, especially the increased bacterial Devosiaceae, Microbacteriaceae, Halieaceae, Vibrionaceae families, and Devosia, Stappia and Vibrio genera, and eukaryotic Isochrysidaceae and TAGIRI1-linage family and Tisochrysis genus. These results indicate that antibiotic treatment may induce a shift in the larval microbiome, which may cause an unstable community structure and in turn affect the oyster health. Full article

The threespine stickleback is a freshwater fish listed as endangered in Portugal, near the southern limit of the species global distribution. However, few measures have been proposed aiming at the conservation of this species in suboptimal environments. From existing databases and specific sampling campaigns, we obtained occurrence data of threespine stickleback for a total of 646 sites. The occurrence data, together with 15 environmental macrohabitat predictors, were used to model the potential distribution of the species using an ensemble of species distribution models. Through the results of our final ensemble, we project that the threespine stickleback occurs predominantly at lower stretches of river systems, where sandy substrate is dominant and flow is higher. Within this region, sticklebacks are also more likely to occur in sites with high levels of rainfall in the driest month, thus avoiding locations with high potential for drying during summer. The species also tends to avoid steep slope areas with high levels of annual precipitation. Based on our results, a map of the species probability of occurrence was generated and river sections were categorized into levels according to their importance for the species’ conservation. Full article