Abstract

Experiments in outdoor nursery pools investigated the effects of stocking density, temperature and pool management on the survival and growth of juvenile yabbies (Cherax destructor) over a six week period. During Feb-May 1988 and 1989 stage 3 juveniles (mean weight 15 mg) were stocked at 100, 200 and 300 m^-2 over successive periods with decreasing mean ambient temperatures of about 21, 19.5 and l7°C. Survival varied from 28 to 91% and increased from an average of 51% to 71% in the second year with the implementation of improved management techniques and the provision of shelter. Increased temperature and lower stocking density significantly increased growth in the 1989 trials. The best mean growth, to 1.12 g, was achieved at low density at the high ambient temperature in 1989; the higher density trials at this temperature gave mean final weights above 0.5 g. The weight distribution in these trials was highly positively skewed with largest individuals achieving final weights above 5 g. Zooplankton biomass, mostly calanoid copepods, was high in some of the 1989 trials and zooplankton made up a significant proportion of yabbie stomach contents. Overall the results show that growth to a mean of 0.5 g over 6 weeks and with 70% survival can be achieved in outdoor nursery pools. Higher production should be achievable with further improvements to nursery management techniques, provision of additional shelters and higher temperatures.

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