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This study was undertaken to explore the systemic metabolic strategies of juvenile grass carp (Ctenopharyngodon idellus) to maintain growth when fed with different dietary protein levels. The optimal growth group and two growing discomfort groups were selected through the basic data, to explain the growth difference from appetite regulation and lipid and glucose metabolism perspective. Three experimental diets were formulated with three dietary protein levels at 200.3, 296.1 and 442.9 g kg -1 , named P1, P2 and P3, respectively. Juvenile grass carp (initial body weight 12.28 ± 0.14 g) were fed with three diets with 3 replications per dietary treatment in an indoor recirculation system for an 8-week feeding trial. Fish fed with diet P2 dietary group showed significantly higher WG, SGR, FI and PER than other groups. Compared with other groups, mRNA expressions of NPY, Y8a and Y8b in fish fed with P2 significantly down-regulated, while the expressions of CCK and CART in fish fed with P3 significantly down-regulated (P < 0.05). With increasing dietary protein levels, G6Pase, GK, PK and PEPCK were all significantly inhibited (P < 0.05). For lipid metabolism, the mRNA expression of ACC in P1 dietary group was significantly higher than P3 dietary group; besides, LPL expression in P3 group was significantly higher than other two groups (P < 0.05). PPARα expression in P2 was significantly lower than other groups (P < 0.05). These results suggested that grass carp fed with P2 (296.1 g kg -1 protein level) showed highest weight gain, contributed to more balanced nutrient metabolism and appetite regulation. Too high dietary protein (442.9 g kg -1 ) should be avoided because it induced lowest PER, body lipid and liver lipid, and inhibited glucose and lipid metabolism in juvenile grass carp.

Ghrelin and obestatin are two gastrointestinal peptides obtained by post-translational processing of a common precursor, preproghrelin. The effect of obestatin on food intake is still controversial. The aim of the present study was to investigate the effects of ghrelin and obestatin on food intake in grass carp, Ctenopharyngodon idellus. Fish received intraperitoneal (IP) injection of saline, ghrelin (100 ng g(-1)BW), obestatin-like (25 ng g(-1)BW) and ghrelin in combination with obestatin-like. Ghrelin stimulation of food intake varied considerably among individual fish with 70.8% eliciting a robust response. In these high-responders, food intake was significantly increased by IP ghrelin within 2 h. Co-administration of ghrelin and obestatin-like resulted in a decrease in food intake, indicating that obestatin was able to antagonize the effect of ghrelin. However, IP obestatin-like alone could not regulate food intake in grass carp. RT-PCR analysis demonstrated that IP ghrelin peptide led to a significant increase in mRNA abundance of NPY, Y8a and Y8b genes compared to saline injected fish, while in combination with obestatin-like peptide decreased ghrelin-induced gene expressions of these three genes. IP sole obestatin-like peptide did not modify the expression levels of NPY, Y8a, Y8b, CART and POMC compared to the control group. Therefore, IP administration of obestatin-like peptide, partially blocking the ghrelin-induced appetite, investigated the possible involvement of obestatin as a mediator of the ghrelin stimulatory action on food intake, at least in "high-responders" grass carp., (Copyright © 2015 Elsevier Inc. All rights reserved.)

Mandarin fish is a typical carnivorous fish, it can accept artificial diet after domestication, which is significantly essential to optimize its artificial diet. Nevertheless, only few studies were conducted on artificial diet of mandarin fish. Therefore, an 8‐week feeding trial was conducted to evaluate the influence of feeding stimulants on growth performance, feed intake and appetite regulation of mandarin fish. In this trial, six diets were formulated, a basal diet contained 80% of Fish Meal without feeding stimulants, named as Control, 0.4% inosinic acid meal, 0.4% L‐Alanine meal, 3% Yeast meal, 3% a commercial squid extract meal and 0.4% betaine meal were added into the basal diet to make five experimental diets, which were named as IM, AM, YM, SVO and BM respectively. At the end of feeding trial, SVO group showed higher feed intake, up‐regulated mRNA expression of neuropeptide Y (NPY) and down‐regulated mRNA expression of pro‐opiomelanocorticoid (POMC) significantly as compared to control group, which suggested that squid extract improved feed acceptability and promoted appetite in mandarin fish. Similarly, compared to control group, SVO group showed low food conversion ratio, high weight gain and SGR, indicated that squid extract enhanced the growth performance. Our results suggested that the appropriate level of squid extract addition could contribute to optimize artificial diet in mandarin fish. [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]

As typical herbivorous fish, grass carp possesses greater capability to utilize carbohydrate than carnivorous and omnivorous fish. However, mechanism of carbohydrate utilization in herbivorous fish was unclear. This study is intended to investigate response of grass carp to insufficient or excessive dietary carbohydrate. Grass carp accepted isonitrogenous diets with different carbohydrate levels (15.90, 21.81 and 45.45 g 100 g −1 ) were cultured. After 8 weeks, weight gain and feed intake were highest in fish fed with medium-carbohydrate diet compared with others. Gene expression data indicated that expressions of glucose-6-phosphatase (G6Pase) were down-regulated and gene expressions of glycogen synthase (GS) were up-regulated in fish accepted lower-carbohydrate diet. In high-carbohydrate group, glucose catabolism was increased by enhanced expressions of glucokinase genes (GK). Meanwhile, fatty acid synthase (FAS) and acetyl coenzyme-A carboxylase (ACC1) genes were significantly up-regulated and lipoprotein lipase and carnitine palmitoyltransferase 1 (CPT1) genes expressions were down-regulate, inducing more lipid deposition. Subsequently, serum cholesterol and total lipid contents were significantly increased, and then induced appetite suppression through up-regulation of leptin and anorexigenic genes expressions. Furthermore, depressed food intake caused lower growth rate in grass carp with excessive carbohydrate intake. [ABSTRACT FROM AUTHOR]