Effects of varying protein level in practical diets on survival,growth, feed utilization and body composition of juvenile tench (Tinca tinca L.)

The aim of this study was to evaluate the effects of practical diets with different protein content on survival, growth, feed utilization and body composition of juvenile tench (Tinca tinca). A 90-day experiment was conducted with 6-month-old juveniles (34.35 mm total length, 0.411 g weight). Six practical diets differing in the protein level were tested: 40, 44, 48, 52, 56 or 60 %. Survival rates ranged from 96.7 to 100 %. The 52 % protein enabled the highest growth (55.49 mm total length, 2.11 g weight, 1.80 % day^?1 specific growth rate) and the lowest feed conversion ratio (1.61) without significant differences (P > 0.05) from the 48 %. Protein productive value ranged from 15.64 to 22.01. The percentages of fish with visible deformities ranged from 1.1 to 4.4 %. The relationship among amino acid profiles of the diets, growth of juveniles, body composition and amino acid requirements of other fish species is discussed. Second-order polynomial regression analysis showed that the optimum dietary protein requirement for maximum growth of juvenile tench may be 52.7 %.