Ji-Dan Ye

Growth, Feed Utilization and Blood Metabolic Responses to Different Amylose-amylopectin Ratio Fed Diets in Tilapia (Oreochromis niloticus)

A feeding trial was conducted in tilapia to determine the growth performance, nutrient digestibility, digestive enzymes, and postprandial blood metabolites in response to different dietary amylose-amylopectin ratios. Five isonitrogenous and isolipidic diets containing an equal starch level with different amylose-amylopectin ratios of 0.11 (diet 1), 0.24 (diet 2), 0.47 (diet 3), 0.76 (diet 4) and 0.98 (diet 5) were formulated using high-amylose corn starch (as the amylose source) and waxy rice (as the amylopectin source). Each diet was hand-fed to six tanks of 15 fish each, three times a day over a 6-wk period. After the growth trial, a postprandial blood metabolic test was carried out. Fish fed diet 2 exhibited the highest percent weight gain and feed efficiency and protein efficiency ratio, whereas fish fed with diet 5 showed the lowest growth and feed utilization among treatments. The digestibility for starch in fish fed diet 1 and 2 was higher than those in fish fed with other diets (p<0.05). The highest activities for protease, lipase and amylase were found in fish fed the diet 2, diet 1, and diet 1 respectively among dietary treatments, while the lowest values for these indexes were observed in fish fed the diet 3, diet 5 and diet 4, respectively. The liver glycogen concentrations in fish fed diets 4 and 5 were found higher than in fish fed other diets (p<0.05). The feeding rate, hepatosomatic index, condition factor, and plasma parmeters (glucose, triglyceride, total cholesterol, high-density lipoprotein cholesterol, and low-density lipoprotein cholesterol) did not differ across treatments. In terms of postprandial blood responses, peak blood glucose and triglycerides were lower after 3 or 6 h in the fish fed with diets 3–5 than in the fish fed diet 1, but delayed peak blood total amino acid time was observed in fish fed with the diets 1 or 2. The lowest peak values for each of the three blood metabolites were observed in fish fed diet 5. The results indicate that high-dietary amylose-amylopectin ratio could compromise growth, but help in reducing the blood glucose stress on fish caused by postprandial starch load.

Growth and metabolic responses in Nile tilapia (Oreochromis niloticus) subjected to varied starch and protein levels of diets

Abstract In the present study, six diets were formulated to contain 24% or 36% protein, and 0, 20%, or 40% starch. The Nile tilapias (Oreochromis niloticus) were fed with the designed diets for 56 days. An overall increasing tendency of percent weight gain, feed efficiency, protein efficiency rate (PER), hepatosomatic index (HSI), and condition factor (CF), whole-body protein and lipid contents, plasma concentrations of triglyceride (TG), total cholesterol (T-CHO) and glucose, liver glycogen contents, liver activities of glucokinase, pyruvate kinase, fatty acid synthetase, lipoprotein lipase (LPL), glucose-6-phosphate dehydrogenase, and malic enzyme with increasing dietary starch level was noted. While the opposite trend was found for feed intake (FI), whole-body moisture and ash contents, liver activities of glucose-6-phosphatase (G6Pase) and phosphoenolpyruvate carboxykinase (PEPCK). Furthermore, all the parameters above were higher in fish fed the 36% vs. 24% protein diets, expect FI, PER, whole-body moisture, liver G6Pase and PEPCK were opposite, and furthermore HSI, whole-body lipid, liver glycogen and LPL were unaffected by dietary protein treatments. The results indicate that Nile tilapia appears to have a more sensitive response to dietary starch level than dietary protein level. Appropriate dietary starch supplementation could help promote the growth of the fish species. Low-dietary protein (24%) allowance may acquire growth comparable to that of Nile tilapia fed 36% protein diets when feed protein is provided only by fish meal with at least 20% starch supplementation.