Abstract

Five formulated pelleted diets and one natural diet were fed to redclaw crayfish held within 9 m² cages fixed to the bottom of an earthen pond in a 6x4 randomised block experiment. Crayfish were stocked at a mean weight of 9.7 ± 0.13 and a density of 6.7 per m² in June and harvested 5 months later in November. Formulated diets varied considerably in composition, particularly crude protein which ranged from 18 to 42%. A sixth natural diet consisted of a combination of whole rice, lupin seed and raw potato. Food was provided to each cage 3 times per week to excess. Numbers harvested from each cage were severely affected by escape and to a lesser extent by water rat predation. In excess of 500 of the 1,440 experimental crayfish were captured outside the enclosures. Considerable growth was achieved in all cages, with one of the pellet diets significantly out-performing all others. Size at harvest from this superior diet averaged 45.8 g. Average size for the other five diets ranged from 31.3 to 38.5 g. The mean size of escaped crayfish was 49 g. Due to the significant reduction in density in each cage because of losses attributed to escape and predation, the nutritional value of each diet was not completely tested. Nevertheless, the results suggest that at the densities which prevailed at harvest, the total protein level of the diet is of minimal significance, and other characteristics including those of a non-nutritional nature may be of greater importance. This supports the notion that a simple diet formulation which feeds the benthic microbial biomass is required for redclaw aquaculture, rather than a nutritionally complete diet formulation which feeds the animal.

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