Definition of a breeding objective for commercial production of the freshwater crayfish, marron ( Cherax tenuimanus)

This study tested the hypothesis that profitability of commercial marron production would be increased by the development of a rapidly growing strain that has a large tail, a proportional claw size, and a high survival, food conversion efficiency, reproductive rate, and fecundity. A profit equation was developed for commercial marron production, and expressed as function of the production characteristics associated with maintenance of the broodstock (growth rate, survival, food conversion efficiency, reproductive rate, and fecundity), incubation of the eggs and hatchlings (survival), rearing of the juveniles (growth rate, survival, and food conversion efficiency), and grow out of the marron (growth rates of the carapace, tail, and claws, survival, and food conversion efficiency). Economic values were estimated for these characteristics when profit was set to zero, and the sensitivity of selection response to potential errors in these estimates was analysed. The results showed that profit was increased by a genetic increase in the growth rate of the juveniles, growth rates of the carapace and tail of the marron, survivals of the broodstock, eggs and hatchlings, juveniles, and marron, food conversion efficiencies of the broodstock, juveniles, and marron, and the reproductive rate and fecundity of the broodstock. By contrast, profit was decreased by a genetic increase in the growth rate of the broodstock, and a genetic increase in the growth rate of the claws of the marron, given that there was a smaller claw weight to carapace weight ratio that was ideal. Growth rate of the tail of the marron was the most economically important characteristic. Its economic value (per genetic standard deviation improvement) was between 4.7 and 11.6 times larger than an improvement in the growth rate of the carapace, survival of the marron, and growth rate of the claws. In turn, growth rate of the tail was between 30 and 7900 times more important than the food conversion efficiency of the marron, and the characteristics associated with the broodstock, eggs and hatchlings, and juveniles. The sensitivity analysis indicated that response to selection was not sensitive to potential errors in the magnitude of the economic values. These results demonstrate that breeding programs for commercial production should concentrate on the improvement of those characteristics associated with the marron, with emphasis on the growth rate of their tail. They also suggest that the economic values