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 native and introduced species respectively. Genetic improvement of farmed stock for aquaculture can be achieved by choosing particular strains, by selective breeding or by producing hybrids of different strains. Studies into the taxonomy and growth of both marron and yabbies have shown variation between geographically isolated populations. This variation may offer potential for selecting strains that demonstrate desirable traits for aquaculture, such as improved growth rates. In addition to selection of wild strains that demonstrate 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 phenotype variation in growth rate, tail and chelae size have been shown to be heritable (h2=0.3-0.6). Recent research into yabby genetics involved assessing growth and reproductive characteristics of geographically isolated populations of yabbies inhabiting a range of ecotypes throughout Australia. Growth rates and size at sexual maturity varied among populations. However, there was no significant difference in the sex ratio between these geographically isolated groups. The main focus of the yabby genetics research has been to develop a method to prevent or reduce reproduction of yabbies. Uncontrolled reproduction in this species results in high densities and smaller animals because growth is density dependent. Preventing reproduction and thereby controlling densities in yabby ponds or dams can be achieved by stocking monosex populations. The stocking of monosex populations results in an estimated 70% increase in gross income. Hybridization of yabby populations was investigated as a method of controlling reproduction. Sterile hybrids were produced by crossing yabbies from geographically isolated populations. These experiments have also revealed a hybrid cross that consistently produces only male progeny. If this all-male hybrid strain performs as well as all-male monosex pond stock, achieved by manual sexing, the production of large, and therefore higher value, yabbies will be increased in the commercial aquaculture industry.