Effects Of Dietary Amylose/amylopectin Ratios On The Growth, Feed Utilization And Intestinal Health Of Tilapia, Oreochromis Nilotictus

The high-amylose corn starch and stick rice were respectively used as the amylose andamylopectin sources in practical diets for tilapia (Oreochromis niloticus). Five isonitrogenousand isolipidic diets with different amylose/amylopectin ratios of0.11(D1),0.24(D2),0.47(D3),0.76(D4) and0.98(D5) were prapared to contain33%crude protein,6.5%crude lipid and28%starch in the diets in the present study. Fish were fed hand-fed to apparent satiation three times aday for a feeding period of42days. The growth performance, postprandial metabolic responses,changes in intestinal microflora and volatile fatty acids of tilapia were presented as follows:1. Weight gain rate, specific growth rate and protein efficiency ratio of tilapia fed D2werethe highest among treatments, and were significantly higher than those fed D3-D5(P<0.05). Thefeed conversion ratio for fish fed D2was the lowest, whereas the value for fish fed D5was thehighest among treatments, and was significantly higher than those in the other dietary treatments(P<0.05). With the increase in the dietary amylose/amylopectin ratio, the apparent digestibilityfor crude protein and ash was first increased and then decreased, the opposite change in crudelipid digestibility was found. The apparent digestibility of starch for fish fed D1and D2weresignificantly higher than those for fish fed D3-D5(P<0.05). The activities of protease in gut andstomach of fish in D1groups were significantly higher than those in the other groups (P<0.05).The activities of amylase in gut in D3-D5groups were significantly lower than those in D1andD2groups (P<0.05). There were no significant differences in blood concentrations ofhigh-density lipoprotein cholesterol, low-density lipoprotein cholesterol, total cholesterol, and inacid phosphatase activity between all treated groups (P>0.05). The results show that the dietaryamylose/amylopectin ratio at0.24was suitable for the growth of tilapia in this study.2. The postprandial plasma contents of glucose, triglyceride and total amino acids of fish inall groups were increased firstly and then decreased with the increase in the dietaryamylose/amylopectin ratio after the fish were given a meal. The fish fed the five diets had similarplasma glucose contents before a meal (P>0.05). The postprandial plasma glucose andtriglyceride values decreased as the dietary amylose/amylopectin ratio increased. The plasmaglucose value in five groups returned to the initial levels at12h after a meal. The plasma triglyceride contents in fed D2-D5groups returned to the initial levels at12h in the postprandial(P<0.05). The postprandial plasma contents of total amino acids in D5group were notsignificantly different (P>0.05). With the increase in the amylose/amylopectin ratio in diets, thetime to reach peak plasma total amino acids was faster than the other parameters. Thepostprandial responses of liver glycogen and muscle glycogen to the amylose/amylopectin ratiowere different in all groups. The concentrations of liver glycogen of fish in D4and D5groupswere significantly higher than those in groups D1-D3before a meal (P<0.05). The results showthat high dietary amylose level enhanced glucose tolerance of tilapia.3. The number of Escherichia coli in the foregut of the tilapia in D1group wassignificantly higher than those in the other groups (P<0.05). The number of lactic acid bacteriaincreased with the increase in the amylose/amylopectin ratio in diets, and the number in D4andD5groups were significantly higher than in D1groups (P<0.05). The number of Escherichia coliin midgut of fish in D1group were significantly lower than those in others (P<0.05). There wereno significant differences in the number of Escherichia coli among D2-D4groups (P>0.05). Themidgut had the similar trend to the foregut with regard to the number of lactic acid bacteria whenthe fish fed the diets containing different amylose/amylopectin ratios. In hindgut, bothEscherichia coli and lactic acid bacteria were not affected by dietary treatments (P>0.05). Theacetic acid contents in digesta increased with the increase in the amylose/amylopectin ratio indiets, and the value in D5group was significantly higher than in others (P<0.05). The propionicacid contents in digesta increased firstly and then decreased as the amylose/amylopectin ratio indiets increased. The propionic acid contents in digesta in D2and D3groups were significantlyhigher than those in D1, D4and D5groups (P<0.05).