Aquaculture Research, 1997, 28, 881–891 Apparent nutrient digestibility of formulated diets by the Australian freshwater crayfish Cherax destructor Clark (Decapoda, Parastacidae) P L Jones & S S De Silva School of Aquatic Science and Natural Resources Management, Deakin University, Warrnambool, Victoria, Australia Correspondence: Dr P L Jones, School of Aquatic Science and Natural Resources Management, Deakin University, PO Box 423, Warrnambool, Victoria 3280, Australia (e-mail: pfj@deakin.edu.au) Abstract 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 4 0 %, 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. © 1997 Blackwell Science Ltd. 881 Introduction Despite the importance of the freshwater crayfish industry worldwide, relatively little information is available which specifically addresses the nutritional and dietary requirements of popularly cultured species (D’Abramo & Robinson 1989; Goddard 1988; Merrick & Lambert 1991). There are also considerable gaps in our knowledge of other important aspects associated with feeding such as the preferred foods, digestion and absorption of nutrients, control of feed intake, and metabolic fate of absorbed nutrients by freshwater crayfish (Brown 1995a). Consequently the formulation of diets for freshwater crayfish is in a stage of infancy (D’Abramo & Lovell 1991). Digestibility studies are pivotal to the successful development of diets for use in aquaculture. Compared to fish, there is a dearth of information available on feed and nutrient digestibility in crustaceans, particularly in freshwater species. The three commercially important parastacids of Australia, Cherax albidus/ destructor Clark, Cherax tenuimanus (Smith), and Cherax quadricarinatus (von Martens) are all seriously under-represented in this regard. In fact, Musgrove (1993) and Villarreal (1991) provide the only other information on the assimilative capacity of Australian parastacid crayfish; both are bioenergetic studies that focus on energy utilization. The primary objectives of the present study were to determine the capacity of C. destructor (commonly called the yabby) to digest the dry matter, protein, ash and crude fibre components of a variety of