Fishes

Ectothermic animals, such as teleosts, have increasingly been exposed to stressful high-temperature events due to global warming. Currently, the effects of thermal stress on skeletal muscle, a key tissue for fish growth, are unknown. This study examined the impact of high-temperature stress on the skeletal muscle transcriptome of rainbow trout (Oncorhynchus mykiss) in control (15 °C) and high-temperature (20 °C) conditions. Additionally, we examined the plasmatic levels of cortisol, glucose, and creatine kinase activity, and examined oxidative damage and autophagy activation in skeletal muscle. High-temperature stress induced significant increases in cortisol and glucose plasmatic levels. Nevertheless, no changes were observed in creatine kinase activity in plasma and skeletal muscle oxidation. Skeletal muscle RNA was isolated and sequenced using the HiSeq Illumina platform. A total of 383,796,290 reads were mapped onto the reference rainbow trout genome. The transcriptomic analysis showed that 293 genes were upregulated in the high-temperature group, mainly associated with autophagosome assembly, amino acid transport, and the glutamine metabolic process. On the other hand, 119 genes were downregulated in the high-temperature group, mainly associated with digestion, proteolysis, and the muscle contraction process. In addition, RT-qPCR of differentially expressed representative genes and Western blot analysis of LC3-II/LC3-I levels confirmed skeletal muscle autophagy induced by high temperature. This study sheds light on intriguing facets of the adaptive response of rainbow trout skeletal muscle to high-temperature stress and provides significant insights into the physiology of autophagy in teleosts. Full article

A twelve-week feeding trial was conducted to investigate the effect of dietary supplementation of a functional immunostimulant mixture (FIM; nucleotides, β-glucan and vitamins C and E) on growth, feed utilization, innate immunity, digestive enzyme activity, hematological parameters, intestinal morphology and inflammatory gene expressions of olive flounder, Paralichthys olivaceus. A fish meal-based basal diet (control) was formulated, and three other diets were prepared by incorporating 0.5, 1.0 and 1.5% FIM into the basal diet (HB0.5, HB1.0 and HB1.5, respectively). Five replicate groups of fish (26.3 ± 0.1 g) were fed one of the experimental diets. Inclusion of 1.5% FIM in the diet significantly enhanced growth and feed utilization. Significantly higher plasma hemoglobin, hematocrit, total protein levels and lower plasma glucose level were observed in the HB1.5 group. Total immunoglobulin content, lysozyme, nitroblue tetrazolium, myeloperoxidase, superoxide dismutase, glutathione peroxidase and catalase activities and immune-related gene expressions of toll-like receptor and perforin were significantly increased at the highest inclusion level. FIM supplementation significantly increased villus height and goblet cell counts. Anti-inflammatory gene expressions were significantly upregulated at a 1.5% level. Dietary supplementation of 1.5% of FIM could improve growth and feed utilization, immune, hematological and intestinal histomorphological parameters of olive flounder. Full article

The age and growth of the blackspot seabream, Pagellus bogaraveo, were determined by examining sagittal otoliths from fish sampled in the eastern Adriatic Sea. A total of 674 specimens (181 males, 90 hermaphrodites, 108 females, and 295 immatures) ranging from 8.80 to 47.27 cm (21.93 ± 9.00 cm) in total length were analyzed. The maximum observed age for the whole sample was 13 years. The sample was dominated by 1-year-old specimens as a consequence of an abundance of juvenile specimens collected by beach seines. Growth was described by the von Bertalanffy growth curve (L_∞ = 52.3 cm, K = 0.15 year⁻¹, t₀ = 0.49 year, R² = 0.97), and the growth performance index (Φ’) was 2.61. The length, width, thickness, and mass of the otoliths were compared with the total length and age of P. bogaraveo from the eastern Adriatic. The analysis showed that the measures were adequate predictors of age. These results can be of value for more effective management measures aimed at the conservation of this species. Full article

Megamouth sharks Megachasma pelagios Taylor, Compagno, and Struhsaker, 1983, are a large-bodied, planktivorous, deep-sea species with peculiar morphology. Since their initial description in the late 20th century, many individuals of different sizes have been reported, but few studies examined ontogenetic changes in body shapes. Here, we assess the growth changes in their heads and fins based on length measurements from nine different-sized individuals (177–544 cm in total length). Bivariate analyses showed that the head becomes larger relative to body length with increasing body size (i.e., positive allometry), whereas the relative size of the caudal fin remains constant (i.e., isometric growth). This trend differs from basking sharks and apparently resembles whale sharks and some baleen whales, although they are all large-bodied filter feeders. Given that relative mouth size is linked to feeding modes, our results suggest that megamouth sharks have different feeding modes from ram-feeding basking sharks and may have some similarity with suction-feeding whale sharks and engulfment-feeding baleen whales. Full article

The present study investigated the effects of dietary supplementation of nanocurcumin (NCur = 150 ppm) in African catfish feed for 15 days along with two doses of florfenicol—a therapeutic dose (FFC1 = 10 mg/kg.BW) and a high dose (FFC2 = 30 mg/kg.BW). Serum biochemical parameters and histopathological changes in liver and kidney tissues were determined post-feeding. Additionally, fish were experimentally challenged with a virulent strain of Aeromonas veronii to explore the fish’s capacity to resist infections. Results indicated that the serum level of total protein was significantly elevated in the FFC2 + Ncur group compared with control, Ncur, and FFC2 groups. Total protein level was also higher in FFC1 + Ncur compared with that of the FFC1 group. Moreover, feeding NCur, FFC1 + Ncur, and FFC2 + Ncur resulted in a significant increase in globulin levels compared to control, FFC1, and FFC2-Fed groups. However, the albumin level was unaffected. Serum levels of AST, ALT, ALP, and urea significantly increased in FFC2-fed fish compared to controls indicating liver damage. The higher dosage of FFC2 induced histological alterations in the liver and kidney architecture, represented by a rupture of the central vein, cytoplasmic vacuolation, hepatocytes necrosis, and severe inflammation. Surprisingly, NCur inclusion improved most of the altered biochemical parameters and mitigated FFC-induced histological damage in the hepatic and renal tissues. Similarly, fish that were fed a combination of both FFC and Ncur showed a higher resistance when exposed to A. veronii infection, as the mortality rates were significantly lower than those of the control group. Our findings indicated that incorporating NCur into the diet can have multiple benefits for the sustainable aquaculture of African catfish. These advantages encompass mitigating drug-induced damage to the liver and kidney tissues, augmenting the therapeutic efficacy of FFC in a synergistic manner and providing protection against A. veronii infections. Full article

The present study evaluated the impact of chronic herbicide (oxyfluorfen; OXY) exposure on catfish, Clarias gariepinus, in terms of growth, hematobiochemical parameters, immune response, antioxidant- and immune-related gene expression, and resistance to monogenean parasites, Quadriacanthus aegypticus. In addition, the protective role of Wormwood, Artemisia cina (AC) against OXY exposure through diet inclusion was also analyzed. The catfish fingerlings were exposed to OXY (1.16 mg/L) for 60 days and fed diets without AC supplementation (control) and with 5% AC supplementation. The results demonstrated that exposure to OXY stunted growth; decreased survival, erythrograms and leukograms, serum protein, and acetylcholinesterase; and negatively altered the antioxidant status. On the contrary, AC supplementation significantly reduced OXY’s negative impacts on growth and hematological, biochemical, and antioxidant balance. In addition, exposure to OXY markedly increased levels of biomarkers of hepatorenal damage, stress indicators, and DNA damage, which were alleviated with AC supplementation. OXY exposure induced immunosuppression manifested by a decrease in lysozyme activities, complement c3, nitric oxide levels, and phagocytic activity. Furthermore, exposure to OXY negatively regulated the expression of immune-antioxidant genes (CAT, GPX1, SOD1, GST, and TGF-Β1). However, it upregulated the expression of CYP1a, IL-1β, and TNF-α in the liver, anterior kidney, and intestine of C. gariepinus. Meanwhile, the addition of AC to the OXY-exposed fish diets notably restored immune components and remedied the altered immune-related gene expressions. Likewise, the AC supplementation significantly alleviated the OXY-induced reduction in the fish survival rate after Q. aegypticus challenge. Accordingly, AC dietary supplementation in catfish diets could alleviate the negative impact of exposure to OXY on growth performance, physiological status, and some immune-antioxidant-related gene expression. Full article

Pinctada fucata, the pearl oyster, is a bivalve primarily cultivated for the production of saltwater pearls. In this study, the genome-wide association study (GWAS) for the growth-related traits and a principal components analysis (PCA) in P. fucata were performed. Genomic parameters of 6 growth-related traits in 60 individuals were estimated by using 4,937,162 single-nucleotide polymorphisms (SNPs). A total of 45 SNPs associated with growth traits were thus identified. Furthermore, 165 candidate genes were identified, including collagen alpha-3 (VI), serine/threonine-protein kinase mos-like harboring significant markers, and histidine-rich protein PFHRP-III-like, which may influence growth-related traits associated with various biological processes. The results of this study can facilitate marker-assisted selection and breeding programs designed to enhance growth and also offer a theoretical foundation for the further development and utilization of genomic resources in P. fucata. Full article

Perch (Perca fluviatilis) in four boreal lakes and sympatric roach (Rutilis rutilis) in two of these lakes were studied by means of gill net sampling, and age and growth were analyzed to explore whether summer temperature affects recruitment and individual growth of the two species differently. Water temperature logging in the lakes showed a highly significant correlation with air temperature. Year-class strength of the perch was significantly positively affected by the summer air temperature, whereas the temperature effect was non-significant for the roach. There was a significant negative effect of year-class strength of one-year-old perch on roach year-class strength in one lake. ln one of the allopatric perch populations, the year-class strength correlation with temperature failed after biomass removal, probably because fishing affected the age structure. July–August air temperature had a significantly positive effect on individual growth rates of two- to five-year-old perch, whereas the effect on roach growth was less clear. The inclination of perch to predate its competitor, roach, as well as conspecifics, as well as accelerated individual growth, were shown to occur more frequently in years with abundant 1+ perch, i.e., the summer after the rise of a strong year-class. Climate warming may potentially favor perch recruitment and growth. Full article

The fish gut microbiota plays an important role in overall health. However, few reports have described the changes in the composition of gut microbiota following infection with pathogenic bacteria in olive flounder (Paralichthys olivaceus). Here, we reported the changes in the gut microbiota composition of flounder after treatment with each of the three pathogenic bacteria (Edwardsiella tarda, Streptococcus iniae, and Vibrio harveyi). Edwardsiella tarda infection decreased the relative abundance of Verrucomicrobia and increased Proteobacteria abundance at the phylum level of the gut microbiota over time. Similarly, Streptococcus iniae infection reduced the relative abundance of Verrucomicrobia. Vibrio harveyi infection caused a decrease in the relative abundance of Firmicutes and Verrucomicrobia and increased Proteobacteria. At the genus level, infection with all three pathogens increased the relative abundance of Ralstonia and Sphingomonas species. Conversely, this infection decreased the relative abundances of Rubritalea, Saccharimonas, and Bacillus species. Therefore, reducing the abundance of Ralstonia and Sphingomonas and increasing the abundance of Rubritalea, Saccharimonas, and Bacillus in the gut microbiota composition of flounder might help maintain a healthy gut microbiota balance. This research might be useful for future studies on improving the health of flounder through gut microbiota regulation. Full article

The Goliath groupers are known to produce characteristic low frequency vocalizations (“calls”) during spawning aggregations and as part of territorial behavior. Acoustic monitoring for Goliath grouper calls around Florida has historically occurred between July and December to capture the spawning season, with a particular focus on August–November. Because of the unique waveform of the Goliath grouper call, we implemented a noise adaptive matched filter to automatically detect Goliath grouper calls from year-round passive acoustic recordings at two wrecks off Florida’s Gulf of Mexico coast. We investigated diel, temporal and environmental factors that could influence call rates throughout the year. Call rates peaked in August, around 0300 EST and just after the full moon. The Goliath groupers were more vocal when background noise was between 70 and 110 dB re 1 µPa. An additional smaller peak in call rates was identified in May, outside of the typical recording period, suggesting there may be other stimuli besides spawning that are eliciting high sound production in this species. Goliath grouper sound production was present year-round, indicative of consistent communication between individuals outside the spawning season. Full article

Effective fisheries management requires an understanding of human dimensions. This study elicited the salient motivations for recreational blue swimmer crab and black bream fishing in Western Australia and whether these views differed depending on the fishing location and/or the characteristics of the fisher. Crab fishers were strongly consumption-orientated and aimed to “catch big crabs” and “catch enough crabs to eat”. Furthermore, 91% consumed their catch, with only 2% practicing catch-and-release fishing. In contrast, 81% of black bream fishers did so for the sport/challenge, with the strongest motivation being to catch a bream considerably above legal size and with food only selected by 15% of respondents; most fishers released caught fish. The marked differences between the fisheries for the two species, which co-occur in the same estuaries, are likely driven by the accessible nature of the crab fishery, ease of catching crabs, the low cost of fishing equipment, and their taste. Fishing for black bream, however, requires more expensive equipment, patience, and a greater skill level. Fishers considered crabbing to be as important as other fishing and outdoor activities, whereas bream fishers considered bream fishing considerably more important, reflecting the trophy nature of this fishery. Full article

Reliable stock identification constitutes an integral component of effective fishery management. Current methods for the identification of putative stock units comprise the analysis of both phenotypic and genetic variability. The present study examined the spatial variation in otolith morphology (shape and asymmetry) and genetic composition of 395 wild-caught Gilthead seabream (Sparus aurata) specimens, collected from the Aegean and Ionian Seas (eastern Mediterranean) between 2014–2018. The degree of scale regeneration (SRD, % of regenerated scales) was used as an indicator to assess the potential presence of aquaculture escapees in the wild-caught samples. Otolith shape and asymmetry analyses showed a phenotypic discrimination between northwestern Aegean and Ionian Gilthead seabream populations. Genetic analyses of nine microsatellite markers revealed higher levels of genetic variation in the wild compared with samples obtained from aquaculture farms. Despite the absence of genetic structure among the wild-caught seabream populations, a low but statistically significant genetic differentiation was found between reared fish and fish collected in the field. The SRD was considered effective in detecting the presence of aquaculture escapees that may have escaped in either early or late rearing phases. Full article

The shell biosynthesis of oysters plays a critical role in protection against environmental stress, in which cartilage matrix proteins (CMPs) determine the mineralogical and crystallographic properties of the shell. In the present study, a cartilage matrix protein (designated as MgCMP1) was identified from the Pacific oyster Magallana gigas (Crassostrea gigas) with the objective of understanding its possible role in shell formation. The open reading frame (ORF) of MgCMP1 was 1815 bp, encoding a polypeptide of 605 amino acids with two von Willebrand factor (VWA) domains. The mRNA transcript of MgCMP1 was expressed constitutively in all examined tissues with a higher level in the mantle, especially highest in the middle fold (MF) of the three folds of the mantle. In addition, the interaction between recombinant protein MgCMP1 (rMgCMP1) and recombinant protein bone morphogenesis protein 7 (rMgBMP7) was identified in vitro. After injection of dsRNA to inhibit the expression of MgCMP1, the mRNA expression level of Mgcollagen I and Mgcollagen X in the MF of the mantle significantly decreased. After pre-puncturing and acidification treatment (pH 7.8), the thickness and length of the new formation shells were lower than those in control group (pH 8.1), and the positive hybridization signals of the MgCMP1 mRNA transcript in the three mantle folds were obviously weakened, especially in the MF, whereas the mRNA expression level of MgCMP1, Mgcollagen I and Mgcollagen X in the MF of mantle decreased significantly. These results suggested that MgCMP1 was involved in regulating the expression of Mgcollagen I and Mgcollagen X in the MF of the mantle in response to ocean acidification (OA). Full article

Twenty-four adult molly fish (Poecilia sphenops, Valenciennes 1846) were collected to study the morphology and distribution of ganglia using histological, immunohistochemical, and electron microscopy and focusing on their relation to the immune cells. The ganglia were classified spatially into cranial and spinal, and functionally into sensory and autonomic. Spinal ganglia (dorsal root ganglia, DRG) contained large close ganglionic cells, enclosed by satellite cells, as well as bundles of both myelinated and non-myelinated nerve fibers. There are glial cells, immune cells and telocytes close to the ganglion. In addition, oligodendrocytes were closely related to myelinated axons. Glial fibrillary acidic protein (GFAP) expression was confined to the glia cells and the nerve fibers in the cervical ganglia next to the gills, and surprisingly, in the large ganglionic cells of the DRG. The vestibular ganglia were large, connected to the hind brain, and contained numerous neurons packed in columns. The cervical ganglia were large and observed around the pseudobranch, head kidney, and thymus. Their neurons are randomly distributed, and nerve fibers are peripherally situated. CD3-positive T-lymphocytes, dendritic cells, and CD68-positive macrophages were in close contact with the ganglia. Furthermore, the ganglia around the head kidney showed positive Iba1-expressing cells. Most ganglion cells and nerve fibers in the DRG, autonomic, and vestibular ganglia showed moderate to strong S-100 immunoreactivity. The enteric glia, CD68-expressing macrophages, and acetylcholine (Ach)-expressing neurons were observed along the muscular layer of the intestinal wall. In conclusion, different ganglia of molly fish displayed direct communication with immune cells which support and maintain healthy ganglionic cells. Full article

The Chesapeake logperch, Percina bimaculata (Halderman) has a disjunct distribution when compared to other species in the subgenus Percina. Members of this subgenus in Pennsylvania include Percina caprodes caprodes (Rafinesque), Percina caprodes semifasciata (DeKay), and P. bimaculata. Historically the Chesapeake logperch was known only from the Susquehanna River and Potomac River basins. Its range is now restricted to the Susquehanna River below Holtwood Dam and upper Chesapeake Bay. It has been extirpated from the Potomac River and the type locality near Columbia, PA. Attempts are being made to reintroduce it into tributaries of the Susquehanna River near Columbia, PA. We postulate that P. bimaculata diverged from a population of Percina caprodes semifasciata. A naked nape and the fact that both of these species do not occur above the fall line in Pennsylvania support such a relationship. Full article

In this study, we evaluated the intestinal contents of Pacific whiteleg shrimp (Litopenaeus vannamei), the visceral mass of razor clams (Sinonovacula constricta) and the water columns and the substrate sediments in different culture-density groups in a L. vannamei–S. constricta tandem-culture model by high-throughput sequencing of the 16S rRNA gene. The results show that the culture density affected the bacterial floral structure of the water columns, substrate sediment and razor-clam gut masses without making significant differences in the bacterial flora structure of the shrimp gut; the Shannon diversity indexes of the bacterial communities in the substrate sediment, shrimp gut and razor-clam gut masses were not significantly different among the density groups, and the Shannon diversity index of the bacterial communities in the water column was higher in the group with higher culture densities; at the phylum level, the dominant bacteria common to the shrimp guts, razor-clam visceral mass, water columns and substrate sediment were Proteobacteria and Bacteroidetes; Chloroflexi was the dominant bacterium specific to the substrate sediment; and Firmicutes was the dominant bacterium specific to the shrimp gut and razor-clam gut mass. We used national standards (GB 17378.4-2007, China) to evaluate the content of water-quality factors through the environmental factors and the genus-level correlation analysis of bacterial flora that follow: the dominant bacterium in the water column, uncultured_bacterium_f_Rhodobacteraceae, was negatively correlated with PO₄³⁻-P; the dominant bacteria in the substrate sediments, uncultured_bacterium_f_Anaerolineaceae and Woeseia, were significantly and negatively correlated with DO; and the dominant bacteria Lactococcus spp. in the razor-clam gut mass and the shrimp intestines were positively correlated with DO. These results show that culture density directly affects water-quality factors, which in turn affect the culture environment and the composition structure of the bacterial flora in a cultured organism. Full article

Aquaculture struggles with sustainability due to the use of fishmeal, and insects are one potential alternative. Insects have low long-chain omega−3 polyunsaturated fatty acid content, and insect-fed fish reflect this in their composition. In total, 500 rainbow trout (Oncorhynchus mykiss, ~46 g) were fed until the fish reached a commercial size (~415 g). Five diets were used: one control based on fishmeal as main source of protein; two with a 50% replacement of fishmeal with yellow mealworm meal (Tenebrio molitor), one with full-fat insect, and another partially defatted; two other diets similar to the one with the full-fat insect, but with the addition of an experimental algal oil rich in omega−3 in two different concentrations (one equivalent to control, the other one to the defatted insect diet). Growth was unaffected, as well as texture and organoleptic profile of the fillets. Lightness, brightness and colour of the fillets were slightly modified by the experimental diets. An increase in omega−3 levels over those of the full-fat insect diet is described. An omega−3 sparing effect was highlighted, causing lipid accumulation in fillets and liver, and a mild increase in oxidative damage. More research is encouraged to evaluate the fatty acid profile of the liver. Full article

Environmental challenges related to open sea cage production of Atlantic salmon have sparked interest in developing commercial-scale semi-closed sea systems for post-smolt Atlantic salmon (100–1000 g). Determining the mass-specific water flow required by post-smolts will largely influence the design and dimensioning of such systems. In this experiment, post-smolts were exposed to four levels of specific water flow: 0.2, 0.3, 0.4, and 0.5 L kg fish⁻¹ min⁻¹. All treatments involved flow-through seawater with full oxygenation, a salinity of 34‰, and a mean temperature of 9.3 °C. The stocking density was kept stable at 75 kg m⁻³. Water pH decreased with reduced flow, while partial pressure of carbon dioxide (pCO₂) and total ammonia nitrogen (TAN) in the water increased. The increase in water CO₂ was reflected in the blood with increased pCO₂, HCO₃⁻, and decreased Cl⁻ in the lowest water flow treatment (0.2 L kg fish⁻¹ min⁻¹), indicating a typical regulatory response to increased water CO₂ over the eight-week experimental period. No negative effects on osmoregulation, external macroscopic welfare, or performance indicators were observed, suggesting that within the time period of this experiment, post-smolts can compensate for reductions in water flow down to 0.2 L kg fish⁻¹ min⁻¹. However, to avoid activating and exhausting potentially energy-costly physiological regulatory mechanisms, it is suggested to keep specific water flow above 0.3 L kg fish⁻¹ min⁻¹ in large-scale operations with semi-closed sea systems at intermediate temperatures. Full article