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Plant protein is the main substitution protein for fishmeal, especially rapeseed meal, and it contains anti‐nutritional factors and toxicants such as tannin. Few studies have identified clear physiological or toxicological impacts of tannin on fish. Here, our experiment evaluated the physiological and toxicological effects of tannin on grass carp (Ctenopharyngodon idellus). Different concentrations of dietary tannin (1.5, 7.2, 19.9, 39.4, 83.2 and 162.0 g kg−1 diet) were tested. Dietary tannin (≥7.2 g kg−1 diet) inhibited feed intake, and the appetite‐promoting gene expression (Grehlin, NPY, Y8a and Y8b), meanwhile, increased the appetite‐inhibiting gene expression (CCK and CART). Moreover, tannin addition reduced feed utilization (dietary nutrient retention, fat depot, activity of protease, lipase and amylase) of grass carp (p <.05). Besides, high dietary tannin (≥39.4 g kg−1 diet) lowered immunity (serum superoxide dismutase and catalase activities and the contents of total protein, albumin, complement component C3 and C4) (p <.05) and damaged the hepatic structure of grass carp, leading to attenuated growth in grass carp. This suggests that grass carp could not tolerate dietary tannin of >19.9 g kg−1. The second trial designed to test the alleviation the negative effect of tannin by tannase. After adding tannase with a dose of 1000 or 1500 U kg−1 to the diets, the weight gain of grass carp fed those diets was significantly increased compared with those fed the tannin and rapeseed meal addition groups (p <.05). Also, when high‐level tannase was supplemented to the control diet, weight gain significantly improved. The decrease in feed intake by high dietary tannin and rapeseed meal was relieved through adding tannase in diet of grass carp, especially when tannase supplemented level reached 1000 U kg−1 diet (p <.05). This study indicates that dietary tannin (≥7.2 g kg−1 diet) negatively affects the growth of grass carp through changing feed intake, feed utilization, immunity and hepatic structure, and addition of tannase reached 1000 U kg−1 diet almost alleviate adverse effects of tannin and rapeseed meal (which included high contents of tannin) on grass carp. [ABSTRACT FROM AUTHOR]

This study was conducted to examine the systemic metabolic strategies of grass carp to maintain lipid homeostasis when fed with low- or high-fat diets. The isonitrogenous diets with different fat levels (9.3, 48.7 and 107.9 g kg − 1 ) were fed to grass carp for 8 weeks. After the feeding trial, the growth rate and feed intake of grass carp fed with low-lipid (LL) diet or high-lipid (HL) diet were lower than fish fed with medium-lipid (ML) diet. Serum triglyceride (TG) and total body fat contents were significantly increased in grass carp with increasing lipid intake. Gene expression data indicated that fish increased hepatic gk and pk expressions to elevate glycolysis, and enhanced acc and fas expressions to accelerate biosynthesis of fatty acid (FA) to adapt to low lipid intake. Meanwhile, fish fed with LL diet decreased hepatic cpt1 expression to depress lipolysis, leading to low contents of serum TG and body fat. In contrast, excess lipid intake increased g6pase , pepck and pparα expressions to stimulate gluconeogenesis and β-oxidative, while decreased acc and fas expressions to reduce lipid synthesis in fish liver. Moreover, increased β-oxidative-induced FA or gluconeogenesis-induced serum glucose might induce the appetite suppression by high dietary fat through modulation of leptin expression. This study could be a reference in the systemic adaptation of lipid metabolism responding to dietary fat in fish. Statement of relevance Systemic adaptation of lipid metabolism responding to dietary lipid. [ABSTRACT FROM AUTHOR]

Insulin receptors have been demonstrated to be involved in embryogenesis, food intake regulation and glucose metabolism in several fish, while more researchis needed for further understanding. In this study, the complete coding sequence (CDS) of insulin receptor a (insra) gene and insulin receptor b (insrb) gene in grass carp were obtained, the CDS were 4068 bp and 4514 bp in length, encoding 1355 aa protein and 1351 aa protein. Both of insra and insrb in grass carp showed high amino acid identities with other fish. Insra and insrb genes were widely expressed in all tested tissues with an overlapping but distinct expressions. The high levels of insra mRNA were distributed in hindgut and heart tissues. The insrb gene showed the highest expression levels in liver and hindgut. We also proved that two forms of grass carp insulin receptors participate in the regulation of blood glucose and might act differently. Phylogenetic analysis confirmed that different isoforms of fish insulin receptors are derived from two distinct genes, which was inconsistent with the generation of mammalian insulin receptors. Synteny analyses of insulin receptor genes showed that genes surrounding the insulin receptor genes were conserved in fish. Arhgef18, PEX11G, humanC19orf45 genes were highly conserved among mammal species. However, no conserved synteny was observed among fish, mammals, avians and amphibians. [ABSTRACT FROM AUTHOR]

Abstract: Neuropeptide Y (NPY) has been established as an important regulator of food intake in mammals. However, the involvement of NPY in the feeding behavior of fish has not yet been fully understood. The present study investigated the role of NPY in food intake in grass carp. The full-length cDNA sequence of gc-NPY was 797bp, and an ORF of 96 amino acids, including the 28-residue signal peptide and 36-residue mature peptide, which had high identities to the NPY of cyprinid fishes. Two receptors Y1 and Y5 which mediate the appetite-stimulating effects of NPY in mammals lost from some of the euteleost genomes. However, sequences of other NPY receptors Y8a and Y8b were obtained from the ESTs library of grass carp in our previous studies. NPY and both Y8 receptors were predominantly expressed in the brain. Cumulative food intake was significantly increased by intracerebroventricular administration of NPY during a 72-h observation period. For better understanding of NPY''s action in grass carp, the mRNA levels of appetite regulators, energy metabolism genes and key digestive enzymes were assessed. The results showed that the mRNA levels of Y8b were significantly increased, while the expressions of cholecystokinin (CCK), cocaine and amphetamine regulated transcript (CART), pituitary adenylate cyclase-activating peptide (PACAP), leptin, leptin receptor (leptinR) and leptin receptor overlapping transcript protein (LEPROT) were significantly decreased after NPY injection. In addition, the marked stimulation of insulin-like growth factor1 (IGF1), insulin-like growth factor 1 receptor (IGF1R), lipoprotein lipase (LPL), Stearoyl-CoA desaturase 1 (SCD1), amylase and trypsin mRNA levels in liver were caused by NPY administration, and the mRNA level of uncoupling protein 1(UCP 1) tended to decrease but not significantly. These results indicate that NPY acts as an orexigenic factor in the grass carp, and Y8b may involve in the feeding regulation. NPY not only affects food intake, but also has marked effects on energy metabolism in grass carp. Moreover, NPY seems to closely interact with other appetite regulators, and the present results provide novel insight into these complex interactions. Further understandings of appetite regulation in fish ultimately have the potential to yield methods for improving feed efficiency in aquaculture. [Copyright &y& Elsevier]

Abstract: The negative effect of dietary phytic acid (PA) in feed intake is a common feature of response to stress in fish, but the regulation mechanism of feed intake is poorly understood. Our study was therefore conducted to estimate the effects of dietary PA on feed intake, feed utilization and feeding-related gene expression in juvenile grass carp. The levels of dietary PA supplementation were 0 (control), 5 (low) and 40 (high) gkg−1 diet, respectively. Triplicate groups (nine 300-L tanks) of grass carp (mean weight, 22.37±0.16g) were fed twice daily (08:00 and 16:00h) to satiation for 8weeks. Supplemental PA decreased the weight gain, feed intake, feed utilization and digestive enzyme activities of grass carp. Dietary PA supplementation decreased the apparent digestibilities of phosphorus, calcium and crude protein. The gene expression levels of cocaine- and amphetamine-regulated transcript (CART) and cholecystokinin (CCK) in the brain were enhanced with the increase of dietary PA supplementation. However, the neuropeptide Y (NPY) and ghrelin mRNA expression levels were reduced in fish fed with low PA, but increased significantly (P<0.05) in fish fed with high PA compared to the control. No significant differences were observed in the gene expressions of NPY receptors Y8a and Y8b among all the groups. The results of this study indicated that the decrease of feed utilization and the increase of CART and CCK gene expressions in the brain might be the main factors for the decrease of feed intake in grass carp caused by dietary PA supplementation. [Copyright &y& Elsevier]