REPLACEMENT OF FISH-MEAL IN DIETS FOR AUSTRALIAN SNAPPER, PAGRUS-AURATUS

The potential for replacing fish meal with soybean and poultry offal m eals in the diets of Australian snapper was assessed. Four diets with 50% crude protein were formulated using fish meal, soybean meal and po ultry offal meal as sources of protein. The control diet had 64% fish meal. The other three diets had 30, 20 or 10% fish meal with the remai ning crude protein contributed by a combination of soybean meal and po ultry offal meal. Weight gain of juvenile snapper (77 g mean initial w eight) decreased as the amount of fish meal decreased below 30%. The r elationship was best described by the equation Y = AX/(X + B) where Y is weight gain, X is fish meal content (%) and, A and B are fitted con stants. Similar results were achieved when snapper were reared under i mproved conditions for growth, i.e., at water temperatures 3-5 degrees C above ambient. At the higher water temperatures, growth rate almost doubled. Apparent digestibility coefficients for energy, phosphorus, crude protein and amino acids were determined for the diets with 64 an d 30% fish meal. Small but significant (P < 0.05) differences were fou nd for energy, phosphorus and methionine availability. However, the di fferences in digestible energy and available nutrients were negligible since both diets satisfied published requirements for warmwater fishe s. The data on growth and FCR were used in a simple economic model whi ch considered fish meal content of the diet, asymptotic growth rate an d relative production costs. This model predicted that relative produc tion costs were: (1) reduced substantially when asymptotic growth rate s increased from 0.4 to 0.8 g per day, and (2) relatively insensitive to replacing up to 50% of fish meal in the diets by soybean meal and p oultry meal. (C) 1998 Published by Elsevier Science B.V. All rights re served.