Genetic improvement of marron Cherax tenuimanus Smith and yabbies Cherax spp. in Western Australia

Marron and yabbies are farmed commercially in Western Australia and are nat ive and introduced species respectively. Genetic improvement of farmed stoc k for aquaculture can be achieved by choosing particular strains, by select ive breeding or by producing hybrids of different strains. Studies into the taxonomy and growth of both marron and yabbies have shown variation betwee n geographically isolated populations. This variation may offer potential f or selecting strains that demonstrate desirable traits for aquaculture, suc h as improved growth rates. In addition to selection of wild strains that d emonstrate desirable traits for aquaculture, further advances in production may be achieved by selection of characteristics in captive stock that are heritable. In marron, moderate proportions of the phenotypic variation in g rowth rate, tail and chelae size have been shown to be heritable (h(2) = 0. 3-0.6). Recent research into yabby genetics involved assessing growth and r eproductive characteristics of geographically isolated populations of yabbi es inhabiting a range of ecotypes throughout Australia. Growth rates and si ze at sexual maturity varied among populations. However, there was no signi ficant difference in the sex ratio between these geographically isolated gr oups. The main focus of the yabby genetics research has been to develop a m ethod to prevent or reduce reproduction of yabbies. Uncontrolled reproducti on in this species results in high densities and smaller animals because gr owth is density dependent. Preventing reproduction and thereby controlling densities in yabby ponds or dams can be achieved by stocking monosex popula tions. The stocking of monosex populations results in an estimated 70% incr ease in gross income. Hybidization of yabby populations was investigated as a method of controlling reproduction. Sterile hybrids were produced by cro ssing yabbies from geographically isolated populations. These experiments h ave also revealed a hybrid cross that consistently produces only male proge ny. If this all-male hybrid strain performs as well as all-male monosex pon d stock, achieved by manual sexing, the production of large, and therefore higher value, yabbies will be increased in the commercial aquaculture indus try.