Effect of dietary lysine level on the growth performance of orange-spotted rabbitfish (Siganus guttatus) fingerlings

The study aimed to determine the optimum dietary lysine level of the orange-spotted rabbitfish Siganus guttatus Bloch, 1787 (average body weight range of 5.2 to 7.6 gxfish(-1)). The feeding trial was conducted for 8 weeks employing six experimental diets which were isonitrogenous, isocaloric, and isolipidic (35% crude protein (CP), 18.3 MJxkg(-1) of gross energy, and 5% lipid). The lysine content ranged from 1.22 g to 2.12 g lysine xkg-1 dry diet (35 to 70 gxkg(-1) CP). Results showed that percent weight gain (PWG), and specific growth rate (SGR) peaked at a lysine level of about 55 gxkg-1 CP equivalent to 1.93 gxkg dry diet-1). Feed efficiencies i.e., protein efficiency ratio and food conversion ratio values as well as survival were not affected by the dietary treatments. Lysine requirement level for juvenile rabbitfish was estimated using both broken-line and quadratic regression analyses of PWG and SGR against dietary lysine levels to be between 15.9 and 18.3 gxkg(-1) diet (=45.3 and 52.3 gxkg(-1) CP).