Apparent nutrient digestibility of formulated diets by the Australian freshwater crayfish Cherax destructor Clark (Decapoda, Parastacidae)

Dry matter (DMD), protein (PD), ash (AD) and crude fibre (CFD) digestibility coefficients were determined for nine different diets fed to the Australian freshwater crayfish Cherax destructor Clark. Diets differed principally in the type and quantity of ingredients used to supply the protein component with fish, meat, soybean, snail, yabby and zooplankton meals comprising the main protein-based ingredients. DMD ranged from 71.8% (soybean meal 40%, Soy-40 diet) to a maximum of 91.4% (zooplankton-based diet). Protein digestibility coefficients were all high and ranged from 88.4% (Soy-0) to 96.0% (Soy-60). Protein digestibility did not appear to be influenced by the principal protein source. Diets that contained a high level of animal or plant-based protein were all highly digestible (PD, 94.1% for the yabby meal-based diet, 80.4% animal 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 coefficients 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 digestibility 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.