Replacement of fish meal by a mixture of animal by-products in juvenile rainbow trout diets

A mixture of animal by-products (MAB) was tested to replace fish meal (FM) in dirts for juvenile rainbow trout Oncorhynchus mykiss. Fish averaging(+/- SD) 0.96 +/- 0.07 g were divided into 15 groups, and 3 groups were fed one of five isonitrogenous diets replacing 0, 20, 40. 60, or 100% of FM protein with similar percentages of MAB (control, MAB20. MAB40. MAB60, or MAB100, respectively). The MAB consisted of 25% meat and bone meal, 24.5% leather meal. 20% squid liver powder, 15% feather meal, 7.5% blood meal (spray-dried). 7.5% poultry by product meal, and 0.25% each methionine and lysine. After 16 weeks of feeding, fish fed diets MAB40, MAB60, and MAB100 exhibited significantly lower growth performance than the fish fed the control and MAB20 diets. Apparent digestibility estimates of protein with different collection times (every 40 min and after 12 and 48 h) did not show, in a feces collection system, protein leaching into the watts for up to 48 h. The MAB substitution of up to 60% of FM protein in diets did not show differences in apparent protein digestibility (85.8 +/- 1.05% for MAB20, 83.1 +/- 0.45% for MAB40 and 82.7 +/- 2.67% for MAB60) compared with the control (85.0 +/- 1.88%). whereas in the MAB100 group digestibility (77.7 +/- 4.42%) was significantly lower than in the other groups. The apparent phosphorus absorption of test diet groups was significantly higher (36.9 +/- 11.12% for MAB20, 24.0 +/- 6.20% for MAB40, 57.1 +/- 5.22% for MAB60, and 57.4 +/- 5.34% for MAB100) than that of the control (8.3 +/- 0.15%). Concentrations of protein and ash in the whole body increased as MAB substitution in dirts increased. The findings suggest that MAB could replace up to 28% of FM protein in diets for juvenile rainbow trout for 16 weeks without adverse growth effects.