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 = −0.493 x + 41.03 x + 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 . [ABSTRACT FROM AUTHOR]