SURVIVAL, GROWTH AND YIELD OF THE AUSTRALIAN FRESH-WATER CRAYFISH CHERAX-DESTRUCTOR IN EXTENSIVE AQUACULTURE PONDS

In April 1989 juvenile Cherax destructor (mean weight 3.9 g) were stoc ked at densities of 3 and 9 m-2 into four 0.2 ha ponds in which a fora ge crop was planted. At harvest in February 1990 mean weights were 24. 9, 33.7, 36.6 and 40.0 g with final mean weight lower in the high dens ity ponds. There was wide variation in individual growth, with weight at harvest varying from 10 to 80 g and only 10.7% of yabbies harvested were premium market size (> 50 g). Reproduction in the ponds provided a second generation of juveniles and large numbers of berried females at harvest. Only 22 to 44% of yabbies stocked were collected at harve st but refilling and further harvesting showed that perhaps 30% of the population had avoided harvest by burrowing. Yabbies below 50 g were restocked to grow-on ponds and more than 50% achieved market size in t he period February-June. The biomass harvested after 10 months varied from 406 to 689 kg ha-1. After grow-on and carry-over harvests, total yield from the original cohort was 666 kg of which 405 kg comprised in dividuals above 50 g. This yield was from an area approximately equiva lent to 1 ha of ponds. Extensive aquaculture using forage crops can pr oduce modest yields of premium size C destructor. Yields may improve w ith further development of forage management and harvesting methods.