This study investigated the effect of different levels of digestible protein (DP) on blood metabolites, hepatic enzyme activity of glycolysis and amino acid metabolism, energy reserves, and the production characteristics of pacu (Piaractus mesopotamicus) during the finishing growth phase. Six semi purified and isoenergetic diets, containing 16.3, 20.1, 23.8, 27.2, 31.5, and 34.8% of balanced DP, provided with essential amino acid balance, were hand-fed to pacu (1100.0 ± 10.3 g, initial weight) three times daily for 7 weeks. The experiment consisted of six treatments, with three randomly arranged replicates (tanks) per treatment. The data obtained from this experiment were analyzed by one-way analysis of variance (ANOVA), and significant differences (p < 0.05) between treatments were determined using Tukey's test. Blood metabolites, except serum ammonia and the hepatic enzymes activities of glycolysis and amino acid metabolism, except hexokinase activity were affected (p < 0.05) by balanced DP. The energy reserve indices, except hepatic total lipid content, were also found associated (p < 0.05) with balanced DP. The test diets significantly (p < 0.05) affected growth performance parameters. Higher dietary proteins led to a greater energy uptake by fish from the protein in feed. Overall, fish fed the intermediate level (23.8%) of balanced DP with digestible energy of 17.95 MJ kg-1 showed better production traits and physio-biochemical health markers. This information could help nutritionists and farmers to develop nutritionally balanced and economically and environmentally sustainable aquafeed for promoting healthy and sustainable production of pacu in intensive culture systems.

Lipoprotein lipase (LPL) functions as a marker of adipocyte differentiation in mammals, but little is known about its role in fish adipogenesis. The aim of this research is to investigate the function of Lpl in adipocyte differentiation in fish. In this paper, we isolated and characterized lipoprotein lipase a (lpla) and lipoprotein lipase b (lplb) from grass carp (Ctenopharyngodon idellus). The complete coding sequence of lpla and lplb was 1587 bp and 1437 bp in length, coding for 507 amino acids and 500 amino acids, respectively. Both lpla and lplb mRNA were expressed in a great number of tissues. During adipogenesis, the level of lpla mRNA reached its maximum at day 2 and then dropped gradually, while the level of lplb mRNA had no significant changes, indicating that lpla and lplb may have different function in the differentiation of grass carp adipocyte. Furthermore, inhibition of lpla by inhibitor of LPL(GSK264220A) at early time points most clearly reduced adipogenesis, whereas these effects were less pronounced at later stages, suggesting that lpla predominantly affects early adipogenesis rather than late adipogenesis. Based on these findings, it can be inferred that lpla and lplb in grass carp may have distinct roles in the differentiation of grass carp adipocyte, and lpla may play an important role in the early adipogenesis rather than late adipogenesis in grass carp.

A 30-day experiment was carried out to know responses of different weaning approaches to the growth and survival of Anabas testudineus larvae. A total of 10800 larvae (Avg. weight 0.016 ± 0.03mg; 3DPH) were randomly distributed in nine treatments (triplicates), including two controls. The strategies are as follows: C1 (Control I): feeding with live food (LF) for 30days and C2 (Control II): feeding with microparticulate diet (MPD) for 30days; T1: LF for 5days and MPD for next 25days; T2: LF for 10days and MPD for next 20days; T3: LF for 15days and MPD for next 15day; T4: LF for 20days and MPD for next 10days; T5: LF for 25days and MPD for next 5days; T6: LF for 5days, then 25% LF replacement by MPD for next 5days, 50% LF replacement by MPD for next 5days, 75% LF replacement by MPD for next 5days, and 100% LF replacement by MPD for last 10days; and T7: LF for 10days, then 25% LF replacement by MPD for next 5days, 50% LF replacement by MPD for next 5days, 75% LF replacement by MPD for next 5days, and 100% LF replacement by MPD for last 5days. Significantly (p < 0.05) higher WG and SGR were recorded in T2 (213.17 ± 0.32, 23.98 ± 0.02) followed by T6, whereas the lowest was found in C2. Significantly higher (p < 0.05) percentage survival was manifested in the T7 (31.83 ± 0.22), followed by T2 (24.75 ± 0.13), and the lowest survival was observed in the C2. The digestive enzyme activities were found to be non-significant (p > 0.05) between different treatment groups. The alanine aminotransferase (ALT), aspartate aminotransferase (AST), lactate dehydrogenase (LDH), and malate dehydrogenase (MDH) were reported to be significantly higher (p < 0.05) in C2 (68.52 ± 0.08, 19.55 ± 0.10, 21.79 ± 0.04, and 0.044 ± 0.01) followed by T1; however, their reduced level was observed in C1. The activity of superoxide dismutase (SOD), catalase (CAT), glucose, and cortisol levels was observed significantly (p < 0.05) higher in C2 and lower in C1 and T2. As per the finding, it can be recommended that the appropriate weaning time for A. testudineus larvae is from 13 DPH onwards, in which larvae can be fed an initial ten days LF afterward MPD and the best weaning strategy can be adopted as in the T7 group for higher survival percentage.

Avermectin is widely used as an important insecticide in agricultural production, but it also shows strong toxicity to non-target organisms. Quercetin is a natural flavonoid that is widely used due to its good anti-inflammatory and antioxidant effects. We believe that quercetin may have a potential therapeutic effect on avermectin poisoning. This experiment was proposed to observe the effect of quercetin on the toxic response to avermectin by observing the toxic response caused by avermectin in the brain of carp. In this project, 60 carp were studied as control group (Control), quercetin administration group (QUE), avermectin exposure group (AVM) and quercetin treatment avermectin exposure group (QUE + AVM) with different interventions to study the effect of quercetin on avermectin. The carp brain tissues were stained and simultaneously analyzed for blood-brain barrier (BBB), oxidative stress indicators, inflammatory factors, and apoptosis using qPCR technique. The results of the study indicate that avermectin exhibits a neurotoxic mechanism of action in fish by decreasing the transcript levels of tight junction protein-related genes, which in turn leads to the rupture of the BBB in the carp brain tissue. Avermectin induced apoptosis in carp brain tissue by increasing oxidative stress response and promoting inflammatory cell infiltration. Quercetin could reduce the accumulation of reactive oxygen species (ROS) in the brain tissue of carp caused by avermectin exposure toxicity, maintain redox homeostasis, reduce inflammatory response, and protect brain tissue cells from apoptosis. The present study confirmed the therapeutic and protective effects of quercetin on neurotoxicity in carp caused by avermectin exposure.

In teleost fishes, activation of the hypothalamic-pituitary-interrenal axis leads to an elevation of circulating cortisol levels as a primary stress response. While acute elevation of cortisol is generally beneficial, long-term elevation, a common characteristic of chronic stress, may lead to detrimental effects on health and physiological performance in fishes. Some stress-mediated behavioural shifts, such as variation along the shy-boldness axis in fish, may influence individual fitness. The present study evaluated the role of cortisol and its mechanisms of action in the exploratory behaviour of the bluegill sunfish (Lepomis macrochirus). Fish were implanted with cocoa butter alone (sham treatment), or cocoa butter containing cortisol, or cortisol and the glucocorticoid receptor antagonist, RU486. A control (untreated) group was also used. Animals were held for 48h following treatment and then were subjected to a Z-maze trial to characterize the exploratory behaviour. Cortisol treatment had no measurable effect on the exploratory behaviour of bluegill sunfish. Despite presenting a higher probability of refuge emergence, fish treated with cortisol combined with RU486 behaved similarly to cortisol-treated and control groups. While these results suggest that cortisol may not be involved in the mechanisms controlling boldness, the influence of cortisol elevation across longer time periods plus validation in different contexts will be necessary to confirm this conclusion.

The aim of our study was to determine the efficacy of utilizing cryopreserved common carp sperm (in comparison to fresh sperm) for propagation at a Hungarian aquaculture facility. The sperm was frozen in 5mL straws using an extender method that was previously tested in common carp. Sperm motility was monitored using a computer-assisted sperm analysis system. The hatching and malformation rates among the specimens were recorded before the stocking of larvae in both groups. The growth (body weight, total length) and survival rates of the fish were measured during the pre-nursing (from May to June: between 1 and 26days post hatching) and grow-out periods (from June to October: between 26 and 105days post hatching) of the same year. The fresh sperm, which was collected and pooled prior to fertilization, showed high MOT (97%), pMOT (92%), VCL (106µms-1), LIN (75%), and ALH (1.84µm). Prior to the fertilization trial of the cryopreserved sperm, low MOT (34%), pMOT (14%), and VCL (61µms-1) values were observed in frozen-thawed sperm. A significantly higher hatching rate was measured in the fresh sperm group (87%) when compared to the cryopreserved sperm group (42%). No significant difference in the overall malformation rate was observed in larvae originating from either the fresh or frozen sperm. A significant difference between the two test groups was observed in the incidence of deformed tails (fresh: 20%, cryopreserved: 55%). Except for one sampling period, no significant difference in the body weight and total length of the fish larvae was found between the two groups throughout the pre-nursing and grow-out periods. A significantly higher larvae survival rate was noted in the fresh sperm (72%) as compared to the cryopreserved group (43%) by the end of the pre-nursing stage. However, no significant difference in survival rate was observed for the cryopreserved sperm (96%) in comparison to the fresh sperm (95%) by the end of the grow-out stage. The results of this study showed, for the first time in large-scale pond culturing, an equal growth and viability in larvae propagated from cryopreserved sperm when compared to fresh sperm (despite the limited available rearing ponds provided by the commercial company).

Free amino acids (FAAs) are believed to play important roles in osmoregulation and buffer capacity in some aquatic animals, such as fishes. However, the potential roles of FAAs have not been systematically summarized and characterized until now. In the present study, the meta-analysis was conducted to investigate the relationships between FAAs and environmental salinities. Twenty published documents were included, accounting for 106 study cases. The effect sizes of total free amino acids (TFAAs), total essential amino acids (TEAAs), and total non-essential amino acids (TNEAAs) to salinity increase were calculated and determined by the restricted maximum likelihood (REML) method. It clearly showed that the elevated salinities significantly induced the contents of TFAAs, TEAAs, and TNEAAs at the ratio of 36%, 27%, and 29%, respectively. Faced to the salinity changes, the contents of FAAs in fishes under freshwater and seawater varied significantly, while the individuals under brackish water displayed relatively constant contents of FAAs. When salinity elevated, the contents of 17 amino acids in muscles significantly increased, suggesting the important roles of FAA metabolism in osmoregulation in fishes. The results also indicated that the effect sizes of TFAAs were positively related to the rates of salinity increases, and exhibited a significant quadratic linear relationship with temperatures. Additionally, the contents of FAAs also showed positive correlation with osmotic pressure, concentrations of plasma Na+, Cl-, and urea, implying their potential roles of FAAs in osmoregulation in fishes. These findings suggested that elevated salinities greatly induced the contents of FAAs in fishes, making a great contribution to maintaining the homeostasis of fishes in response to environmental salinity changes.

Skeletal muscle myoblastic cell lines can provide a valuable new in vitro model for the exploration of the mechanisms that control skeletal muscle development and its associated molecular regulation. In this study, the skeletal muscle tissues of grass carp were digested with trypsin and collagenase I to obtain the primary myoblast cell culture. Myoblast cells were obtained by differential adherence purification and further analyzed by cryopreservation and resuscitation, chromosome analysis, immunohistochemistry, and immunofluorescence. A continuous grass carp myoblast cell line (named CIM) was established from grass carp (Ctenopharyngodon idellus) muscle and has been subcultured > 100 passages in a year and more. The CIM cells revived at 79.78-95.06% viability after 1-6 months of cryopreservation, and shared a population doubling time of 27.24 h. The number of modal chromosomes of CIM cells was 48, and the mitochondrial 12S rRNA sequence of the CIM cell line shared 99% identity with those of grass carp registered in GenBank. No microorganisms (bacteria, fungi, or mycoplasma) were detected during the whole study. The cell type of CIM cells was proven to be myoblast by immunohistochemistry of specific myogenic protein markers, including CD34, desmin, MyoD, and MyHC, as well as relative expression of key genes. And the myogenic rate and fusion index of this cell line after 10 days of induced differentiation were 8.96 ~ 9.42% and 3-24%, respectively. The telomerase activity and transfection efficiency of CIM cell line were 0.027 IU/mgprot and 23 ~ 24%, respectively. These results suggest that a myoblast cell line named CIM with normal biological function has been successfully established, which may provide a valuable tool for related in vitro studies.

Aquaculture routine practices may cause stress induction on the fish and compromise their welfare affecting the production. This experiment aimed to evaluate the potential links between handling during culture with stress responses and growth on Senegalese sole (Solea senegalensis). We worked with two fish cohorts in terms of initial body weight and culture stage: Trial 1 included specimens in the fattening stage (226 ± 4.96 g) and Trial 2 animals in the pre-fattening stage (27.20 ± 0.44 g). The tested culture protocol, which lasted 6 and 4 months for Trial 1 and 2, respectively, mainly reduced handling-derived stressors in the experimental tanks via lowering routine samplings to a minimum. This decrease of the handling-derived stress was reflected in both trials with lower concentration of circulating cortisol in blood plasma from the experimental fish when compared to controls. Moreover, the proposed protocol promoted higher growth in the fish cultured in the less disturbing protocol in Trial 2. Higher specific growth rates and mean body weight and length were reported. In order to further explore the potential beneficial effects of our protocol, we studied the musculoskeletal from Trial 2 gene expression of key genes regulating glucocorticoid signaling pathway and apoptosis: glucocorticoid receptors 1 and 2 (gr1, gr2), heat shock protein 90 AA (hsp90aa), and caspase 6 (casp6). In line with the cortisol reduced level in this trial, gr1, hsp90aa, and casp6 genes showed lower expression in the samples coming from the experimental group. The findings of this study provide valuable information to the aquaculture industry for the management of Solea senegalensis stress and welfare.

The present study aims to compare the gene expression of three different fish species (common carp, tilapia, and trout) with varying levels of fatty acids (FA). Based on transcriptome analysis and RNA sequencing, various genes and their associated metabolic pathways are identified. Pathways are categorized based on the genes they encode. Genes that were differentially expressed and their promoter's methylation patterns were revealed by RNA-seq analysis in common carp. Furthermore, fatty acid-enriched pathways, such as ARA4 and adipocytokine signaling, were also identified. Many genes and pathways may influence tilapia's growth and omega-3 content. Using the mTOR pathway, trout with differential expression were discovered to be involved in producing omega-3 fatty acids. This study revealed major pathways in fish species to produce omega-3 fatty acids.