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 pr oduction 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 o f the production characteristics associated with maintenance of the broodst ock (growth rate, survival, food conversion efficiency, reproductive rate, and fecundity), incubation of the eggs and hatchlings (survival), rearing o f the juveniles (growth rate, survival, and food conversion efficiency), an d grow out of the marron (growth rates of the carapace, tail, and claws, su rvival, 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 grow th rate of the juveniles, growth rates of the carapace and tail of the marr on, survivals of the broodstock, eggs and hatchlings, juveniles, and marron , food conversion efficiencies of the broodstock, juveniles, and marron, an d the reproductive rate and fecundity of the broodstock. By contrast, profi t 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, give n that there was a smaller claw weight to carapace weight ratio that was id eal. Growth rate of the tail of the marron was the most economically import ant characteristic. Its economic value (per genetic standard deviation impr ovement) was between 4.7 and 11.6 times larger than an improvement in the g rowth 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 charac teristics associated with the broodstock, eggs and hatchlings, and juvenile s. The sensitivity analysis indicated that response to selection was not se nsitive 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 th e marron, with emphasis on the growth rate of their tail. They also suggest that the economic values are suitable for implementation in breeding progr ams, even when future production systems and market conditions are uncertai n. The hypothesis tested in this study was supported. Profitability of comm ercial 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. (C ) 1999 Elsevier Science B.V. All rights reserved.