Title: The effects of substituting fishmeal with rapeseed meal at three protein levels on growth and body composition of Nile tilapia fingerlings (Oreochromis niloticus)

A 6-week feeding experiment was conducted to evaluate the effects of substituting fishmeal with rapeseed meal in the diets of Nile tilapia (Oreochromis niloticus) with mean initial weight of 3.1 g. Seven different experimental diets were used in this feeding trial. Six diets were calculated isoenergetic with gross energy (GE) of 16,800 MJ/kg while the seventh diet was calculated to have GE of 21,861 MJ/kg, crude protein of 34% and fat 25%. Three of the six prepared diets (1, 3 and 5) were formulated at three different protein levels (35, 27.5 and 20%) respectively using fishmeal as the main protein source. Part of fishmeal in diets 1, 3 and 5 was substituted with rapeseed meal to form diets 2, 4 and 6 respectively while the crude protein levels were maintained. The substitution of fishmeal with rapeseed meal was 54% in diet 2 (35% CP), 80% in diet 4 (27.5% CP) and 72% in diet 6 (20% CP). Growth performance and feed utilisation were significantly affected when fishmeal was replaced with rapeseed meal. Rapeseed meal supplementation has significant effects on body composition at low protein level. Based on the growth and feed utilisation results, 54% replacement of fishmeal with rapeseed meal is not recommended in the diet of Nile tilapia at the size of 3.1 g.