Studies On The Cobalt And Manganese Requirements In Juvenile Pearl Gentian Grouper (Epinephelus Lanceolatu♂×E.fuscoguttatus♀)

Minerals, such as iron(Fe), copper(Cu), manganese(Mn), zinc(Zn), selenium(Se), and cobalt(Co) are little in animals, they play an important role on the growth,development, reproduction and immunity of the body. In recent years, studies on the trace element in aquaculture is increasing, but there are few studies on the Co and Mn requirements of fish. What is more, some studies concentrated on inorganic form of Co and Mn. Thus, the form of organic, especially the form of cobalt and manganese chelated with amino acid were rarely reported.Cobalt methionine and manganese methionine are one of new types of chelating agent. The rate of methionine to cobalt or manganese are 2:1. Both the cobalt methionine and manganese methionine are absorbed in pinocytosis by amino acid,with easing the absorption antagonism among trace element. Thus, the absorption utilization rate of the cobalt and manganese are greatly improved, and the absorption of other trace element are increased. The midintestine of fish is alkalinity, so the solubility of inorganic trace element are low under the condition of alkaline. Thereby,the digestion and absorption rate are reduced. The trace element chelated with amino acid can be absorbed directly. Existing researches showed that the of utilization of organic trace element by fish is higher than inorganic forms.Pearl gentian grouper belonging to Epinephelus, Serranidae, and is a hybrid grouper made by E. lanceolatu and E. fuscoguttatus. It has rapid growth, high disease resistance and high economic value.The purpose of this paper is to study the application prospect of dietary cobalt methionine and manganese methionine in grouper feed, and preliminarily determine the cobalt and manganese requirements of juvenile grouper. The first chapter summarized the research progress on the trace element requirements of seawater fish.The second chapter studied the effects of dietary cobalt methionine on growth performance, mineral deposition and hepatic enzyme activities in juvenile grouper.The third chapter studied the effects of dietary manganese methionine on growth performance, mineral deposition, hepatic enzyme activities in juvenile grouper.Study 1: Cobalt is one of the essential elements for fish, with various of biological functions, including in growth promotion, blood production, reproduction,and immunity. In this study, we evaluated the effects of dietary cobalt methionine(Co Met) on growth performance, mineral deposition and hepatic enzyme activities in juvenile grouper(Epinephelus lanceolatu♂×E. fuscoguttatus♀). Six extruded isonitrigenous and isoenergetic diets were formulated by supplementing the basal diet with Co Met, providing actual Co contents of 0.30, 1.75, 3.42, 6.73, 12.56, or 25.50mg·kg-1 diet which are fed to groups designated D1, D2, D3, D4, D5 and D6,respectively. Each diet was randomly assigned to triplicate groups of 20 juveniles(60.02±0.42 g). The experiment was conducted for 8 weeks in plastic cylinder tanks in an indoor recirculated feeding system. The weight gain rate and specific growth rate(SGR) of the juveniles both increased and then decreased with higher Co Met levels, and both were significantly higher in the D3 group than in the other groups(P<0.05). The feed conversion rate declined with low doses of dietary Co Met but nicreased with higher doses,, and the lowest feed conversion rate was observed in the D3 group. There were no significant differences in the moisture or ash contents of the muscle among the treatment groups(P>0.05). The crude protein content of the muscle was clearly reduced by dietary Co Met, and was significantly lower in the D5 and D6 groups than in the other groups(P<0.05), whereas it did not differ in groups D5 and D6(P>0.05). The muscle of fish fed the D6 diet had the highest crude lipid content(P<0.05), and the muscle of fish fed the D4 diet had the lowest crude lipid content(P<0.05). The Co contents of the liver, intestine, vertebrae and muscle were significantly increased with Co Met supplementation(P<0.05). The Co deposition rate in the whole body was markedly increased(from 0.30 to 6.73 mg/kg diet) by dietary Co(P<0.05), and then plateaued in the fish fed diets with Co contents of 12.56(D5)and 25.50 mg/kg(D6). The Fe, Cu, and Zn contents of the liver increased from group D1 to group D3 and then declined from group D4 to group D6(P<0.05). The Mn content of the liver was significantly reduced by dietary Co Met(P<0.05). The glutathione peroxidase activity of the liver increased and then decreased as Co Met increased(P<0.05), and was naximum in the fish fed the D5 diet(P<0.05). Fish fed the D5 or D6 diet showed significantly lower hepatic malonaldehyde contents(P<0.05). The arginase activity in the liver was significantly increased by dietaryCo Met(P<0.05), and was highest in the D6 group(P<0.05). The carboxypeptidase A activities in the livers of the D4 to D6 groups were significantly higher than those in the D1 to D3 groups(P<0.05), but did not differ among the D4 to D6 groups(P>0.05).In conclusion, under the experimental conditions used here, the optimum Co requirement for the juvenile grouper was 3.25 mg/kg diet(53.28 mg Co Met/kg diet)based on the broken-line regression of SGR.Study 2: An 8-week feeding trial was conducted to estimate the effects of dietary manganese on growth, mineral deposition and enzyme activities in juvenile grouper,Epinephelus lanceolatu×E. fuscoguttatus. The basal diet was formulated to contain520 g·kg-1 crude protein from casein and fish meal. Manganese methionine was added to the basal diet at 0, 2.5, 5, 10, 20 and 40 mg Mn·kg-1 diet providing 7.48, 10.34,13.76, 19.72, 31.00 and 53.91 mg Mn·kg-1 diet, respectively. Each diet was randomly fed to triplicate groups of juveniles, and each tank was stocked with 20 fish(60.06±0.68 g). The manganese content in rearing water was monitored and kept below 0.01 mg·L-1. Results showed that the weight gain ratio(WGR), protein efficiency ratio(PER), specific growth rate(SGR), Mn contents in whole-body, liver and vertebra, and activities of hepatic Mn superoxide dismutase(Mn-SOD), total SOD(T-SOD), and glutathione peroxidase(GSH-PX) were significantly improved by dietary Mn supplementation(P<0.05). However, dietary Mn did not affect arginase(DArg) activity. The fish fed the basal diet with 7.48 mg·kg-1 of Mn had the highest feed conversion ratio(FCR)(P<0.05). No significantly differences were found on the Cu and Zn contents in whole body by supplementing dietary Mn. Supplemented Mn in diets had significantly effects on liver and vertebral trace element deposition(P<0.05). Fish fed the basal diet had the highest Fe and Zn contents in vertebra(P<0.05). There were no significant differences on hepatic pyruvate decarboxylase(PDC) activity with supplemented Mn levels below 13.76 mg·kg-1, but it would be higher when dietary Mn levels above that value. As biomarker of oxidative stress,malondialdehyde(MDA) content in liver was significantly higher in fish fed the basal diet(P<0.05). The survival ratio(SR) were all 100% among treatments. Using the broken-line models based on SGR, dietary Mn requirement of the juvenile grouper was estimated to be 12.70 mg·kg-1(191.55 mg Mn Met·kg-1 diet).