Dietary ecology of the yabby, 'Cherax destructor', and the silver perch, 'Bidyanus bidyanus': An investigation into polyculture potential

Abstract

Polyculture can increase the productivity of each unit of water in an aquaculture system through the production of complementary species in a single body of water. In Australia, the aquaculture industry is focussed on producing a small number of high trophic order species. As a result, the possibilities of systems using complementary species without trophic overlap are limited, even more so in the freshwater industry. Crayfish/finfish polyculture, however, is one grouping which shows particular promise. Techniques for the production of the yabby, 'Cherax destructor', and the silver perch, 'Bidyanus bidyanus', in eastern Australian are established. However, we are unaware of research that has scientifically investigated polycultural production of these species. One aspect through which traditional polyculture aims to increase production is the use of non-competing species. This will maximise usage of food sources within a pond and minimise negative interactions between species. The contribution of naturally occurring food items to the growth and production of 'C. destructor' and 'B. bidyanus' in aquaculture ponds is unknown. To address this, we utilised stable isotope techniques to identify what food sources are consumed and how this changes with protein level in formulated feeds. Both species were found to consume plant and animal biomass within a pond, therefore, there was a significant dietary overlap between the two species. 'B. bidyanus' grew better when supplied with formulated feed containing higher protein levels. Growth was further enhanced through consumption of naturally occurring food items. 'C. destructor' also consumed naturally occurring food items, however, consumption conferred no growth advantage. Variation in dietary protein, at the levels tested in our study, also had no effect on 'C. destructor' growth. Cannibalism in 'C. destructor' aquaculture is common and the causes are largely unknown. Supplementation of 'C. destructor' diets with yabby flesh showed some indication that cannibalism may be reduced, although further research is required. Shelter significantly increased survival of 'C. destructor'. Surprisingly, its value to crayfish was not enhanced in the presence of 'B. bidyanus'. Aquarium based trials showed polyculture of 'C. destructor' and 'B. bidyanus' increased total biomass yield over monoculture of either species alone. Further research is required to undertake large scale production trials to test whether the production advantages in our aquarium based study can occur on a commercial level.