APPARENT NUTRIENT DIGESTIBILITY OF FORMULATED DIETS BY THE AUSTRALIANFRESH-WATER CRAYFISH CHERAX DESTRUCTOR CLARK (DECAPODA, PARASTACIDAE)

Dry matter (DMD), protein (PD), ash (AD) and crude fibre (CFD) digesti bility coefficients were determined for nine different diets fed to th e Australian freshwater crayfish Cherax destructor Clark. Diets differ ed principally in the type and quantity of ingredients used to supply the protein component with fish, meat, soybean, snail, yabby and zoopl ankton meals comprising the main protein-based ingredients. DMD ranged from 71.8% (soybean meal 40%, Soy-40 diet) to a maximum of 91.4% (zoo plankton-based diet). Protein digestibility coefficients were all high and ranged from 88.4% (Soy-0) to 96.0% (Soy-60). Protein digestibilit y did not appear to be influenced by the principal protein source. Die ts that contained a high level of animal or plant-based protein were a ll highly digestible (PD, 94.1% for the yabby meal-based diet, 80.4% a nimal protein; PD, 95.2% for the Soy-60 diet, 80.2% plant protein), AD coefficients were highly variable and ranged from 17.3% (snail-based diet) to 73.2% (yabby meal diet). Crude fibre digestibility coefficien ts were as high as 57% (diet A30: fish/yabby/soybean meal-based diet). No apparent trend occurred in dry matter digestibility in relation to the ash or crude fibre components of the diets. The high digestibilit y coefficients obtained for a wide variety of diet-types suggests that C. destructor has a versatile digestive system which may reflect its natural polytrophic omnivorous feeding behaviour.