Search Results (1,303)

The Chinese longsnout catfish (Leiocassis longirostris) is an economically important freshwater fish in China; however, its wild resources have declined dramatically in recent decades. Understanding the genetic structure of Chinese longsnout catfish populations is crucial to guide breeding programs and fishy restoration. In this study, 15 highly polymorphic microsatellite DNA loci were used to evaluate its genetic diversity and population structure. Chinese longsnout catfish populations show high genetic diversity; they do not show significant genetic differentiation or systematic geographic pattern of variation. From the upper to the lower reaches of the Yangtze River, the genetic diversity of Chinese longsnout catfish populations showed an increasing trend. The Gezhouba and Three Gorges dams, which physically divide the Yangtze River into upstream and mid-downstream sections, did not contribute to the genetic differentiation of Chinese longsnout catfish populations. Hence, the source of broodstock is not critical for within-river breeding programs and stock enhancement to restore the wild population. In addition, possible effects of dams on differentiation among populations are crucial and long-term evaluation is essential. Full article

Comparing co-occurring species may provide insights into how aspects of ecology may play a role in influencing their microbial communities. During the 2019 commercial shrimp trawl season off coastal Georgia, swabs of skin, gills, cloaca, and gut were taken for three species of batoids (Butterfly Ray, Bluntnose Stingray, and Atlantic Stingray) and one shark species (Atlantic Sharpnose) for high-throughput sequencing of the V4 region of the bacterial 16S rRNA gene. White muscle was analyzed for stable isotopes (δ¹³C and δ¹⁵N) to evaluate potential niche overlap in these four sympatric mesopredators. Significant differences were found in both δ¹³C and δ¹⁵N signatures across species, suggesting a degree of resource partitioning. When examined within tissue type, the host species had a weak effect on β-diversity for cloaca and skin, with no differences found for gill and gut samples. However, network analysis metrics demonstrated a stronger species-specific effect and distinct microbial community relationships were apparent between the shark and batoids, with the former having tighter networks for both internally- and externally-influenced tissues (gut/cloaca and skin/gills, respectively). Despite overlapping habitat use, species’ microbiomes differed in their organizational structuring that paralleled differences in stable isotope results, suggesting a mediating role of species-specific ecology on bacterial microbiomes. Full article

Size differences are common in the aquaculture of fishes. In the larviculture of cannibalistic species such as pikeperch, they majorly influence mortality rates and consequently provoke losses in the aquaculture industry. With this study, we aim to reveal molecular differences between small and large pikeperch of the same age using a set of 20 genes associated with essential developmental processes. Hereby, we applied a general study design to early and late larval pikeperch before the onset of piscivory to explore the causes of growth differences in these developmental groups. The analysis of the expression levels showed developmental but not size-related differences in PGC1A, TGFB1, MYOD1, MRF4, and the collagens COL1A1 and COL1A2. Furthermore, increased head lengths were found in larger late larvae compared to their smaller conspecifics. While no uniquely size-related expression differences were found, the expression patterns of PGC1A in combination with TGFB1 as regulators of the citric acid cycle indicate a possible influence of mitochondrial energy metabolism. Furthermore, expression differences of MYOD1 and MRF4 point out possible temporal advantages of myogenetic processes in the larger late larval group and hypothesise growth advantages of the larger late larvae resulting from various influences, which provide a promising target for future research. Full article

Invertebrates show great diversity in their responses to neural damage. Numerous invertebrate phyla, including gastropods, can replace all or a portion of their nervous systems. Aplysia species have been utilized extensively in toxicology, ecology, and neuroscience because their neurological systems react to bodily harm by releasing trophic substances that can stimulate non-neural tissue regeneration and induce changes in the nervous system. This study aims to assess the putative role of hemocytes of Aplysia depilans (Gmelin, 1791) by analyzing the presence of Toll-like receptor 2, inducible nitric oxide synthetase, and, in particular, vimentin and α-tubulin, molecules potentially implicated in the process of neural regeneration. The results demonstrate that all the aforementioned proteins are present in hemocytes, suggesting their role in the defense response and their possible contribution to the neuronal regeneration process of this gastropod. These data provide deeper insight into the internal defense system of this mollusk. Full article

In the Mediterranean Sea, and in marine areas worldwide, for most locations, data on species presence and abundance are generally poor or non-existent. When available, these data are generally reported only at small scale and/or for short temporal series. In this study, the investigation of abundance and size trends, along with some ecological aspects of the data-poor species Scorpaena porcus, commonly known as the Black Scorpionfish, was undertaken using FEK (Fishers’ Ecological Knowledge) abundance and size trends, with some ecological aspects. The results clearly indicated a sharp reduction in both abundance and size over the last 21 years (2001–2021) of this species in the central Mediterranean Sea. The causes of this decline, and the importance of FEK, as well as Local Ecological Knowledge (LEK), in research and the assessment and management of biological resources are discussed. Full article

Aquaculture of ornamental marine fish is often conducted in recirculating aquaculture systems (RAS) using artificial seawater. Considering the cost of salts to produce artificial seawater (salinity 35‰), we investigated the effect of different salinities (5, 15, 25, and 35‰) on survival, growth, and oxidative stress responses of juvenile clownfish Amphiprion ocellaris. All fish died when reared at salinity 5‰, but at all other salinities survival was ≥95% in the other treatment groups. There was no influence of salinity on growth and oxidative stress responses of clownfish reared at salinities 15, 25, and 35‰, except for the activity of glutathione S-transferase (GST) of fish reared at 25‰, which was significantly lower compared to those reared in salinity 35‰. The salinity of home aquariums is usually 35‰, so even though clownfish can be reared in brackish water, they need to be transferred to full strength seawater (35‰) in order to be commercialized. Therefore, we also evaluated the responses of acute transference of fish reared at 15 to salinity 35‰. There were no mortalities associated with acute salinity transference and no oxidative damage was observed either. The total capacity against peroxyl radicals (ACAP) was immediately increased after fish were placed in salinity 35‰, and remained high after 168 h (7 days), helping fish to deal with oxidative threats. In conclusion, it is possible to rear juvenile clownfish at 15‰ without harming growth or inducing oxidative stress, possibly reducing costs of water salinization. They can be transferred from brackish water to salinity 35‰ immediately before going to the retail market, with no mortality or oxidative damage. Full article

Selenium, an essential trace element, exerts beneficial effects on aquatic animals when present in suitable concentrations. This study investigates the effect of dietary nanometer selenium (Nano-Se) on the muscle selenium accumulation, nutrient composition, and antioxidant ability of Paramisgurnus dabryanus spp. Nano-Se was supplemented in the basal diets at levels of 0, 0.1, 0.2, 0.4, and 0.6 mg/kg. Three hundred fish, averaging 5.21 ± 0.06 g, were randomly divided into five groups and fed the experimental diet for 6 weeks. Fish with a dietary Nano-Se supplement of 0.2 mg/kg exhibited activities of SOD, GSH-Px, AKP, and CAT in the liver, which were significantly higher (p < 0.05) compared to the control diet, while MDA content was significantly lower (p < 0.05) in the 0.2 mg/kg group. The muscle selenium content significantly increased (p < 0.05) at ≥0.2 mg/kg Nano-Se levels. The highest levels of essential amino acids, EAA/TAA, and EAA/NEAA ratios were observed in fish fed 0.2 mg of Nano-Se. Thus, this study recommends incorporating 0.2 mg of Nano-Se per kg in the diet to enhance antioxidant defense, selenium content, and nutrient composition. Full article

Discus fish, Symphysodon spp., have a unique parental care strategy where the fry feed on their parents’ skin mucus after hatching. Here, lipidomics was employed to compare the skin mucus lipid profiles of male or female discus fish during parental and non-parental care. By multivariate statistical analysis, clear separations were found between parental and non-parental female and between parental and non-parental male discus. In the comparison between female discus in the parental and non-parental stages, a total of 107 differentially expressed lipids (DELs) were observed, of which 23 showed increased levels during parental care. For male discus, a total of 108 DELs were found, of which 46 displayed increased levels during parental care. The main DELs were phosphatidyl ethanolamine and phosphatidylinositol, mainly involved in arachidonic acid and sphingolipid metabolism pathways. Further, by comparing parental male and female discus, we found 47 DELs involved in the glycerophospholipid metabolism pathway. Diglyceride showed a higher concentration in the skin mucus of parental females, while phospholipids showed a higher level in that of parental males. Our results revealed changes in the skin mucus lipid profiles of discus fish during parental care, as well as sex-dependent differences between parental fish. Full article

An increase in the consumption of food fish, combined with a decrease in the harvest of fish, is driving the aquaculture industry at a fast pace. In parallel with the growth in the aquaculture sector and resulting stresses, the prevalence of diseases in farmed fish can increase. Although effective administration and prophylaxis are the main factors safeguarding fish species against diseases, recent approaches to mitigate the response caused by typical stressors include the uses of dietary additives. Microalgae are one of the main sources of nutrients, namely protein, lipids, vitamins, minerals, and pigments in aquatic animal diets. Numerous studies have proved the beneficial effects of microalgae on fish growth performance, feed utilization, disease resistance, and immunological and antioxidant activities. On the other hand, the administration of different microalgae to fish feed can enhance the fillet quality from several aspects, leading to an overall improvement in fillet shelf-life. This review focuses on the evidence supporting the beneficial effects of various microalgae on biochemical and organoleptic aspects as well as the proximate composition of carcasses in fish species. Full article

In this study, twelve polymorphic microsatellite loci were screened to evaluate the genetic diversity of five yellow drum (Nibea albiflora) populations in the Zhoushan Sea region of the East China Sea, including one wild population (WP), one artificially propagated population (common population, CP), and three breeding populations (parent population, F4; all-female population, AF; and neo-male population, NeoG). The results of genetic diversity analyses showed that all five yellow drum populations had relatively high genetic diversity, with the highest in WP and the lowest in NeoG. Genetic structure analyses showed that the level of genetic differentiation among populations was low, with that between CP and F4 being the largest, whereas that between CP and WP was the smallest. Mutation–drift equilibrium analysis showed that the five populations likely did not experience a recent bottleneck. Our results suggest the CP population was the most suitable for large-scale release for stock enhancement, and precautionary measures shall be taken for the AF population before it is used for cage culture to avoid potential genetic concerns of the wild population. Nevertheless, further genetic diversity monitoring is needed to evaluate genetic effects and avoid the negative impact of excessive genetic differentiation between breeding and wild populations. Full article

The pirarucu, Arapaima gigas, is an emblematic endangered Amazon osteoglossid with high potential for aquaculture development. In this study, we report the in vivo collection of semen from pirarucu for the first-time and a complete description of the spermatozoa ultrastructure using scanning and transmission electron microscopy (SEM and TEM). The spermatozoon of pirarucu is biflagellate with no acrosomal cell, comprising a spherical head (8.26 ± 2.19 µm²), a short intermediate piece region and two long flagella (68.34 ± 5.69 µm). The nucleus is spherical and electron-dense, and at its base, there are two nuclear fossae where the centrioles are found. The anterior part of the flagellum is positioned at the lateral base of the nucleus, forming an intermediate piece. Lateral to the intermediate piece, an abundant number of mitochondria are present and occupy most of the cytoplasmic volume. The two flagella were found with a 9 + 2 axonemal structure (nine peripheral doublets and two central microtubules). The central microtubules are aligned with two side fins formed laterally by the axoneme plasma membrane. Side fins were observed from the anterior region to the posterior end. The results show that the spermatozoa of A. gigas are biflagellate, mitochondria-rich and robust, corroborating the external fertilization characteristic of the species. The novel description of sperm morphology presented herein will contribute to advancing the knowledge of and aiding future research on the reproductive biology of this species. Full article

A 56-day feeding trial was conducted to evaluate the effect of different dietary protein sources on the growth performance, muscle flavor substances, and quality structure of Triploid Crucian Carp. Three isonitrogenous (32.00%), isolipidic (8.00%), and isoenergetic (18.00 MJ kg⁻¹) practical diets were formulated. These diets consisted of fishmeal as the animal-derived protein source (AP), a combination of soybean meal and rapeseed meal as the plant-derived protein source (PP), and a mixture of fishmeal, soybean meal, and rapeseed meal as the mixed protein source (MP). Each diet was randomly assigned to triplicate tanks of fish and each tank was stocked with 25 fish (11.5 ± 0.4 g). The fish were fed until apparent satiation twice a day. The results showed a significant enhancement in the growth performance of Triploid Crucian Carp in the AP group compared with both the MP and PP groups (p < 0.05). Dietary plant derived protein can remarkably reduce the crude lipid content and increase the moisture content of the whole body and the dorsal muscle (p < 0.05). The antioxidant ability of fish in the PP group and MP group was better than that in the AP group (p < 0.05). Regarding free amino acids composition of muscle, the contents of glycine, methionine, and lysine were significantly enhanced in the AP group, while the histidine content was significantly increased in the PP group (p < 0.05). In terms of texture, dietary plant protein significantly improved the muscular hardness, gumminess, and chewiness. The activities of intestinal trypsin and alkaline phosphatase (ALP) of fish in the PP group were significantly higher than that in the AP group (p < 0.05). The expression levels of hepatopancreas TOR and IGF1 genes in the PP group were significantly higher than that in the MP group (p < 0.05). The present results indicate dietary fishmeal significantly improved the growth performance and muscular flavor glycine content, while dietary plant-based protein increased crude protein content, antioxidant ability, and muscular texture performance of Triploid Crucian Carp. Full article

The world’s oceans and seas host >100 known strains of thraustochytrids, a common group of marine eukaryotic unicellular protists, residing in diverse marine habitats, with many others to be isolated and cultivated. The thraustochytrids have become of considerable industrial interest due to health benefits gained from their high percentages of valuable bioactive compounds, revealing the needs for the isolation of new potential strains. Employing a recently developed isolation methodology (use of cell culture medium), we assess initial culture conditions and growth paces of newly isolated thraustochytrid cells (thraustochytrid sp. BSH), originated from the colonial tunicate Botryllus schlosseri, residing on Helgoland Island, Germany. Cells were cultivated under static versus agitated conditions, along with two inoculation sizes (0.5 × 10⁶ and 1 × 10⁶ cells/dish) and in three vessel types (35 mm Petri dishes and T25 and T75 flasks; containing 3, 5 and 15 mL medium, respectively). Cultures were observed under regular microscopy, confocal microscopy and H&E staining. While cells in all conditions grew fast, results revealed the superiority of agitated cultivation in T75 flasks inoculated with 0.5 × 10⁶ cells/dish (6.41 ± 1.91-fold increase/week). Further, 18S rDNA revealed high similarities (99.5–99.8) of strain BSH to two thraustochytrid strains from Monterey, California (USA), B. schlosseri colonies, elucidating a new understanding of these animals-protists associations. Full article

Due to overfishing and marine pollution, the status of fishery resources and the ecological environment in the sea areas have considerably changed. The proliferation and release of fishery resources have become the main means of human intervention to maintain and conserve the resource populations. The annual output of Sepiella japonica (S. japonica), once one of the four major seafood species in the East China Sea, has now recovered to a level of 4000 t. However, do the traditional spawning grounds of S. japonica still exist? Have the spawning grounds shifted? These scientific questions are worthy of attention. Based on the survey data of fishery resources and environment at 120 stations in coastal Zhejiang waters from 2015 to 2022, the spatial and temporal distribution and resource center of gravity of S. japonica in springtime were analyzed. Random forest (RF) was used to explain the importance of six environmental variables, including water depth, sea surface temperature, sea surface salinity, chlorophyll a, pH, and dissolved oxygen. The generalized additive model (GAM) nonparametric smoothing function was used to analyze the relationship between environmental factors and the distribution of S. japonica inhabiting the offshore areas of Zhejiang province, and the effects of environmental factors on spawning habitat selection of S. japonica were revealed. This study found that there was a significant interannual variation in S. japonica resources, with an overall increasing trend in the resource. The spawning grounds were mainly distributed in the Jiushan Islands Marine Reserve, the Dachen Islands Marine Reserve, and their nearby sea areas. The resource peaked at latitude 28.3° N. Additionally, the most important variables affecting the distribution of S. japonica were depth of water, followed by sea surface salinity, pH, dissolved oxygen, sea surface temperature, and chlorophyll a. S. japonica mainly inhabited sea areas with a depth of 15~25 m and a sea surface salinity of 26~32. When the pH ranged from 7.6 to 8.3, dissolved oxygen ranged from 6 to 9 mg/L, sea surface temperature ranged from 14 to 17 °C, and chlorophyll a ranged from 2.5 to 5 µg/L, S. japonica was more likely to be present. This study provides insights into the spatial distribution of S. japonica in offshore Zhejiang province, offering a reference for the rational utilization and scientific protection of this resource. Full article