All the trials were done in ambient seawater with an average temperature of 23.3F2.3jC (the average yearly temperature in the Red Sea). The diet used was similar for all feeding trials and was formulated based mainly on fish meal and fish
oil including a vitamin mix (900 g fish meal, 90 g fish oil kg 1 feed) and pelleted using a laboratory pellet mill. Fish meal was chosen as the only protein source because of its balanced amino acid profile. Crude protein (CP) content of the feed was on average 563 g, lipid 177 g, ash 153 g and gross energy (GE) 20.20 MJ kg 1.