Abstract
A 120-day feeding trial was conducted to investigate the effects of dietary sorghum starch on growth performance, feed utilization, apparent digestibility coefficient (ADC) and some hepatic enzyme activities regulating glycolytic and gluconeogenic metabolic pathways of fingerlings hybrid red tilapia (Oreochromis mossambicus × O. niloticus) with mean initial body weight of 10.9 ± 0.2 g. Five diets containing graded levels of sorghum starch (15%, 20%, 25%, 30% and 35%) were formulated. The results demonstrated that weight gain (WG), specific growth rate (SGR), protein efficiency ratio (PER) and net protein utilization (NPU) values increased with increasing dietary sorghum starch up to 30%. Hepatosomatic index, plasma glucose, triglycerides, liver glycogen and liver lipid concentration of fish significantly increased with increasing dietary sorghum starch level (P<0.05). ADC of starch decreased significantly with increasing sorghum starch level over 30%. However, whole body compositions and ADC of protein and lipid showed no significant differences. Dietary sorghum starch supplements tended to enhance gluconokinase and pyruvate kinase activities of the liver but insignificant differences were observed in activities of hexokinase, phosphofructokinase-1, fructose-1, 6-bisphosphatase and glucose-6-phosphatase in the liver for all dietary treatments. Based on WG and FCR results, the appropriate dietary sorghum starch supplementations of fingerlings hybrid red tilapia (O. mossambicus × O. niloticus) can be incorporated up to 30% of diet.
Highlights
Carbohydrates are the most economical source of energy available in abundant quantities at low prices and have a protein-sparing effect in some low-protein diets and for binding other ingredients [1,2]
The present study showed that weight gain (WG), specific growth rate (SGR) and CF of hybrid red tilapia significantly increased with increasing dietary sorghum starch level from 15% to 30%, while feed conversion ratio (FCR) had a contrary tendency
This study showed that the dry matter, protein and ash contents of whole body and muscle were not affected by dietary sorghum starch levels, which agreed with the findings in European sea bass [23], gilthead sea bream [23,53] and silver carp [57]
Summary
Carbohydrates are the most economical source of energy available in abundant quantities at low prices and have a protein-sparing effect in some low-protein diets and for binding other ingredients [1,2]. Feed supply and feed costs are amongst the greatest challenges for the development of sustainable fish farming. The aquaculture industry is searching for feed ingredients that can be used to formulate cheap fish feed [2]. It was noticed that fish meal and fish oil contribute 75% of the protein and 35% of the energy in aquaculture feed [3]. It has been estimated that the cost of feed constitutes 74% of total costs for farm-made feeds and 92% for manufactured pellet feeds [4]. The cost of aquaculture production can be reduced by efficient feed formulation [5]
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