Search

Ammonia is one of the major environmental pollutants in freshwater aquatic systems that affects the survival and growth of organisms. In the present study, a nine-week experiment was conducted to investigate the chronic toxicity of ammonia on survival and selected hematological parameters, antioxidant ability, and histological structure in juvenile Chinese blunt snout bream, Megalobrama amblycephala. Fish were exposed to one of five different ammonia concentrations (0, 5, 10, 15, and 20 mg L −1 total ammonia-N, pH = 7.86 ± 0.41, temperature = 28.23 ± 0.79 °C). Growth performance of fish in the high-ammonia treatment was lower than that of fish in the control group. The survival rate in the group exposed to the highest ammonia-N concentration (20 mg L−1) was significantly lower than that of the control group. The lowest level of white blood cell count (WBC), red blood cell count (RBC), hemoglobin, hematocrit, and plasma glucose and the highest level of plasma ammonia, cortisol and aspartate transaminase were observed in fish exposed to ammonia-N at 20 mg L −1 compared with the control group. The liver superoxide dismutase (SOD), catalase (CAT), and glutathione peroxidase (GPX) activities in fish exposure to 20 mg L −1 ammonia-N group were significantly lower than those in the control group, while oxidative stress indices (levels of malondialdehyde, MDA) was significantly higher than those in the control group. Regression analysis found that growth performance, plasma parameters, hematological parameters, and antioxidant status of fish were significant linear correlated to ammonia-N concentration. Fish exposed to various concentrations of ammonia displayed histopathologic alterations in both gill and liver tissue. Furthermore, morphological examination by transmission electron microscopy revealed that gill tissues displayed vacuolation of the cytoplasm, damaged mitochondria, increased heterochromatin, and intense desquamation of pavement epithelial cells on the gill lamellae. Our findings suggest that the stress responses induced in juvenile blunt snout bream by chronic exposure to ammonia are not limited to simple growth inhibition, but are accompanied by changes in oxidative stress, plasma parameter effects, and alterations in the histology of the liver and gill. Blunt snout bream had a dose-dependent effect on ammonia-N. We preliminarily suggest that the level of plasma ammonia, MDA, CAT, AST, FER, and SGR can be used as an indicator for chronic ammonia-N toxicity, but further research and verification are needed in the future.

This study was conducted to examine the effects of fish meal (FM) replacement by rice protein concentrate (RPC) supplemented with xylooligosaccharides (XOS) on the growth, intestinal digestive and absorptive capabilities and amino acid metabolism of blunt snout bream. Fish were randomly divided into six groups, and were fed with the control diet (containing 10% FM), the RPC diet (FM entirely replaced by RPC) and the RPC diet supplemented with 0.5, 1.5, 2.3 and 3% XOS, respectively, for 8 weeks. Fish fed the RPC diet obtained significantly lower values in daily growth index, feed efficiency ratio, nitrogen and energy retention and plasma concentrations of methionine, leucine, phenylalanine, lysine and histidine compared to the control. However, the supplement of 1.5% XOS restored these parameters to the levels similar to the control group. Fish fed the RPC diet showed no statistical difference in intestinal lipase, alkaline phosphatase and Na+K+-ATPase activities compared to the control group, but exhibited lower protease, carboxypeptidase A, aminopeptidase N and γ-glutamyl transpeptidase activities. However, these effects were reserved with the administration of 1.5% XOS. Also, the transmission electron microscopy analysis showed a significantly lower microvilli length in the mid-intestine of fish fed the RPC diet compared to the control, but it improved significantly with the supplementation of XOS. Hepatic activities of alanine transaminase, aspartate aminotransferase and glutamate dehydrogenase were significantly lower in fish fed the RPC diet compared to the control, but they improved with the supplementation of 1.5% XOS. Similarly, fish fed the RPC diet obtained relatively low expression levels of the target of rapamycin (TOR) and ribosomal protein S6 kinase 1 but higher expressions of eukaryotic translation initiation factor 4E-binding protein 2 in the intestine, liver and muscle. Opposite trend was observed in fish fed the RPC diet supplemented with 1.5% XOS. Overall, these results showed that RPC supplemented with 1.5% XOS could completely replace FM in the feed of blunt snout bream without any adverse effect on the growth performance, intestinal enzymes activities, gut morphology, amino acid metabolism and TOR signaling.

A 10-week feeding trial was performed to evaluate the effects of different types and levels of carbohydrates in growth performance, apparent digestibility coefficients and skin-associated mucosal non-specific immune parameters in blunt snout bream (Megalobrama amblycephala). Fish were randomly fed four diets containing two carbohydrates (glucose and starch) diets and two carbohydrates levels (330 and 440 g kg−1). High carbohydrate levels remarkably increased the weight gain rate (WGR), apparent digestibility of dry matters, protein and carbohydrates, body crud protein content, plasma levels of aspartate transaminase (AST), and skin-associated mucosal levels of immunoglobulin M (IgM), HDL cholesterol, lysozyme (LZM), advanced the transcriptions of mucin 2 (Muc2), mucin 5b (Muc5b) and apolipoprotein A-I (apoA-I), whereas the opposite was true for feed conversion ratio (FCR), plasma levels of IgM, skin-associated mucosal levels of major histocompatibility complex (MHC) and β-Defensins, and the transcriptions of heat shock protein 60 (Hsp60). In addition, carbohydrate types of glucose remarkably increased the survival rate, apparent digestibility of dry matters, protein and carbohydartes, body crud ash, plasma levels of total protein (TP), globulin (GLB), immunoglobulin M (IgM), complement C3 and complement C4 and the transcriptions of Muc5b. Whereas the carbohydrate types of starch remarkably increased viscerosomatic index (VSI), hepatosomatic index (HSI), condition factor (CF), abdominal fat percentage (AFP), apparent digestibility of liquid, advanced the transcriptions of Muc2, apoA-I and heat shock protein 70 (Hsp70). Significant interactions between different types and levels of dietary carbohydrates were also observed in WGR, apparent digestibility of dry matters, protein and liquid, body crud ash, plasma levels of TP, albumin (ALB) and AST, skin-associated mucosal levels of major histocompatibility complex (MHC) and β-Defensins, and the transcriptions of Muc2 and Muc5b. Our results indicate that inclusion of high level of glucose in the diet of blunt snout bream could improve growth performance, nonspecific immunity, and increase the efficiency of protein, which is suggesting that high level of glucose could be used in feed production. However, the proportion of the specific formula of glucose using in feed needs further study.

Nitrite (NO2−) contamination of water can severely impact the health of aquatic life and is a major concern for commercial aquaculture. In order to study the effect of nitrite on Aristichthys nobilis, we investigated the oxygen-carrying capacity, NF-κB/HIF-1α pathway, and the gill tissue structure under nitrite stress. In the current study, bighead carp (initial weight 180.05 ± 0.092 g) were exposed to nitrite (48.634 mg/L) for 96 h and then for 96 h recovery test. After nitrite exposure for 6 h, hypoxia-inducible factor-1α (HIF-1α) and nuclear factor-κB (NF-κB) mRNA expression increased significantly in the gill of bighead carp (P

A nine-week feeding trial was performed to determine the dietary linolenic acid (LNA; 18:3n–3) requirements of juvenile blunt snout bream. Six iso-nitrogenous, semi-purified diets were prepared with different concentrations of LNA (0–25 g/kg). Dietary LNA had no significant effects on survival rate. However, final fish weight, weight gain (WG), specific growth rate (SGR) and feed efficiency ratio (FER) increased with increasing dietary LNA concentrations up to 20 g/kg. Dietary LNA increased muscle LNA and total n-3 polyunsaturated fatty acid (PUFA) contents, but decreased total saturated fatty acid content. Fish fed 20 g/kg LNA had the highest plasma alkaline phosphatase activity, total protein, albumin and white blood cell count levels. Additionally, fish fed 20 g/kg LNA had higher triglyceride levels than control fish. Plasma glucose increased with increasing dietary LNA concentrations. Superoxide dismutase and glutathione peroxidase activities significantly increased with increasing dietary LNA concentrations up to 15 g/kg. Based on SGR and FER, the optimal dietary LNA requirements of juvenile blunt snout bream were 17.5 and 15.6 g/kg respectively.

The present study was conducted to compare the effects of using soybean peptide as a particle substitution in fish meal on the growth performance, digestive function, and immune responses of yellow catfish. Four isonitrogenous and isoenergetic experimental diets were formulated by replacing 0 % (D-0), 20 % (D-20), 35 % (D-35), and 50 % (D-50) of fish meal with soybean peptide for 8 weeks. The results showed that the final body weight (FBW), weight gain rate (WGR), and specific growth rate (SGR) significantly increased in the dietary D-50 group compared to those of the control group (D-0 group), and the feed conversion ratio (FCR) significantly decreased compared to that of other groups. The D-50 group had higher levels of serum globulin concentration (GLB), alkaline phosphatase activity (ALP), and total nitric oxide synthase activity (tNOS) than the control group, respectively. In addition, the anterior intestine protease activity of the D-20 group was significantly higher than that of the control group and the D-50 group. The serum alanine aminotransferase (ALT) activity of the D-20 dietary group was also significantly higher than that of other groups. Furthermore, the challenge with Aeromonas hydrophila caused mortality in all groups but it was lower in the group of fish that received D-50 than that of the control group. Therefore, we concluded that the D-50 diet could be used to improve immune responses and growth performance and to replace the fish meal in the diet of yellow catfish.

This study aimed to investigate the effects of fishmeal (FM) replacement by rice protein concentrate (RPC) with a xylooligosaccharides supplement on the growth performance, antioxidant capability and immune response against Aeromonas hydrophila in blunt snout bream (Megalobrama amblycephala). Fish (46.85 ± 0.34 g) were randomly assigned to one of 6 diets, namely the control diet (containing FM), the RPC diet (FM replaced by RPC) and RPC diet supplemented with 0.5, 1.5, 2.3 and 3% XOS respectively, for 8 weeks. After the feeding trial, fish were challenged by Aeromonas hydrophila for 96 h with the blood and liver sample obtained at 48 and 96 h respectively. The results showed that the final weight, weight gain and protein efficiency ratio of fish fed RPC diet were significantly (P 0.05) lower than that of the control group, whereas the opposite was true for FCR. However, the supplement of 1.5% XOS remarkably (P 0.05) improved these parameters compared to the control diet. Plasma total iron binding capacity of fish fed the RPC diet showed little difference (P 0.05) with that of the control group, but it enhanced significantly (P 0.05) with the supplement of 1.5% XOS compared to the control group. After bacterial infection, plasma lysozyme (LYM), complement 3, complement 4, myeloperoxidase (MPO), acid phosphatase (ACP) and alkaline phosphatase activities, as well as immunoglobulin M, levels all increased significantly (P 0.05) with the maximum value is attained at 48 h, then they decreased significantly (P 0.05) with further increasing time at 96 h. Similar results were also observed in liver superoxide dismutase (SOD), catalase (CAT) and glutathione peroxidase (GPX) activities as well as malondialdehyde (MDA) content. Regarding dietary treatment, these parameters of fish fed RPC diet showed little difference (P 0.05) with those fed the control diet but were significantly enhanced (P 0.05) when RPC diet was supplemented with 1.5-2.3% XOS, except for hepatic (MDA) content which showed an opposite trend compared to the control group. After 96 h of challenge, the relative percentage survival (RPS) of fish fed XOS was significantly higher (P 0.05) than that of fish offered the control and RPC diet. In addition, significant (P 0.05) interactions between dietary XOS and sampling time were also observed in plasma LYM, MPO, ACP, and hepatic SOD, CAT, GPX, MDA, as well as RPS. In conclusion, this study indicated that dietary supplementation of 1.5%XOS could significantly improve the growth performance, antioxidant capability, innate immunity and A. hydrophila resistance of blunt snout bream fed diets with FM replaced by RPC.

This study aimed to characterize the full-length cDNA of AMPKα2 in Megalobrama amblycephala, and evaluate its potential role in glucose homeostasis and carbohydrate metabolism. The cDNA obtained covered 1942bp with an open reading frame of 1635bp encoding 545 amino acids. Multiple alignments and phylogenetic analysis revealed a high homology (91-100%) among most fish and higher vertebrates. This AMPKα2 mRNA predominantly expressed in muscle, liver and brain, while little in gill and intestine. Then, the AMPKα2 expressions were determined in the muscle, liver and brain of fish subjected to a glucose load (injected intraperitoneally with 0, 1.67 and 3.34g glucose per kg body weight) and after a 12-week feeding trial (fed two dietary carbohydrate levels: 30% and 43%), respectively. After the glucose load, plasma glycemia peaked at 1h in fish. Thereafter, it decreased significantly to the basal level at 8h. However, AMPKα2 expression in muscle, liver and brain all decreased significantly during the first 2h, then returned to the basal value at 24h. Unlikely, tissue AMPKα2 expression of fish receiving saline solution increased significantly during the whole sampling period. Additionally, high-carbohydrate diet enhanced its expression in liver and muscle, but not that in brain. These findings indicated that the AMPKα2 gene shared a high degree of conservation with that of the other vertebrates. Muscle, liver and brain AMPKα2 expressions were highly induced by glucose administration. Furthermore, high dietary carbohydrate modified its expressions in these tissues.

This study aimed to investigate the effects of dietary emodin, high-dose vitamin E and their combination on the growth of Megalobrama amblycephala and its resistance to acute crowding stress. The fish were randomly divided into four groups: a control group fed with basal diet, and three treatment groups fed with basal diet supplemented with 60 mg/kg emodin (the emodin group), 500 mg/kg vitamin E (the vit E group), and 60 mg/kg emodin together with 500 mg/kg vitamin E (the combination group). After 60 days, the fish were exposed to acute crowding stress for 24 h. The results showed that the weight gain of the vit E group, specific growth rate of the vit E group, total serum protein concentration (TP) of the vit E group, serum lysozyme activity of the emodin group, serum superoxide dismutase (SOD) activity of the emodin group, hepatic heat shock protein 70 (HSP70) levels of the vit E group and the emodin group, and serum alanine aminotransferase (ALT) activity of the combination group significantly increased while the weight gain and specific growth rate of the combination group significantly decreased compared with the control group before stress. After crowding stress, the vit E group had improved serum TP 12 h post-stress, hepatic SOD activity 24 h post-stress, and hepatic HSP70 mRNA levels 12 and 24 h post-stress while the emodin group had enhanced serum SOD activity 12 and 24 h post-stress and hepatic HSP70 mRNA levels 12 and 24 h post-stress, as compared with the control. However, the serum cortisol content of the three treatment groups 12 and 24 h post-stress, ALT activity in the vit E group and emodin group 24 h post-stress, and serum alkaline phosphatase and liver catalase activity in the combination group 24 h post-stress were lower than those in the control group. The cumulative mortality was lower in the emodin, vit E, and combination group after Aeromonas hydrophila infection compared with the control group. Therefore, dietary supplementation with 60 mg/kg emodin or 500 mg/kg vitamin E can improve HSP70 mRNA levels and antioxidant capabilities, resistance to crowding stress, and growth in M. amblycephala . However, the combination of emodin and vit E does not have a synergistic effect in M. amblycephala .