Optimisation of dietary protein level for rearing juvenile spotted scat (Scatophagus argus Linnaeus, 1766)

An 8-week feeding trial was conducted to determine the optimum dietary protein level for growth, feed utilisation, chemical composition and amino acid profile in juvenile spotted scat (Scatophagus argus). Five isoenergetic diets containing 31.70, 35.39, 40.71, 45.88 and 51.48% crude protein (T1-T5 respectively) were formulated and fed to triplicate groups of S. argus (4.92 +/- 0.06 g, n = 15 for each group). The percent weight gain (WG), specific growth rate (SGR) and average daily gain (ADG) showed significant quadratic response to dietary protein level with the highest values observed in the T4 group. The feed conversion ratio (FCR) and feed intake (FI) showed significant quadratic response to the dietary protein level, with the highest efficiency in the T3 and T4 groups. Crude protein and most amino acid levels increased with increasing dietary protein. The optimum dietary protein level for tested parameters of this species amounted to 41-45%. However, WG, SGR, ADG, FCR and FI showed subtle and/or insignificant differences between the dietary protein levels of 35.39 and 45.88% (T2-T4 groups). These results suggest that diets containing similar to 35% protein can be a practical and cost-effective option for rearing juvenile spotted scat.