Effects of dietary protein levels on growth performance and haemato-immunological parameters of juvenile genetically improved farmed tilapia (GIFT), Oreochromis niloticus

This study evaluated the effect of dietary protein level on growth performance and haemato-immunological parameters of juvenile genetically improved farm tilapia, Oreochromis niloticus, fed five iso-caloric diets of dietary protein levels 25-45 %, formulated using white fish, casein, gelatine, soybean, cottonseed and rapeseed meals as protein sources. The diets influenced the significant increase in final weight, condition factor and whole body lipid composition (P < 0.05). Conversely, the 25 % protein diet resulted in a significantly (P < 0.05) lower weight gain and higher feed conversion ratio than the 30-45 % protein diets. Protein efficiency ratio and protein retention efficiency of the fish significantly reduced as dietary protein level increased (P < 0.05). Meanwhile, hepatosomatic index increased with dietary protein. Haemato-immunological parameters, white blood cell, red blood cell, immune globulin M, superoxide dismutase and lysozyme activity, were not significantly affected by the dietary protein levels (P > 0.05). Quadratic regression model, y = -0.493x (2) + 41.03x + 267.3, informed that 41.6 % dietary protein supported maximum growth of tilapia juvenile. Fish fed 35 % protein diet had a similar growth performance, but better protein utilization than the 40 % group. These results demonstrated possibility of reducing protein level in commercial feeds, thus lowering feed costs .