Abstract

The interaction between red claw crayfish, Cherax quadricarinatus, and tilapia grown together under intensive culture was investigated in a series of experiments. Growth and survival of red tilapia were not affected by red claw in a small-scale intensive system. Moreover, the fish grew better with crayfish than in monoculture. Interspecific aggression and competition for food were studied using video recording, with special reference to the relative size of red claw and tilapia. Large fish out-competed the crayfish, and even small fish ingested some of the feed on the substrate despite being excluded from the feed patch by the crayfish. The effects of different feeding regimes on growth of red claw and tilapia in communal culture were investigated using fish and crayfish of different relative sizes. The feed was spatially separated by feeding the fish floating pellets and crayfish sinking pellets vs feeding all animals sinking pellets, and temporally separated by feeding the fish during the day and crayfish during the night vs feeding all animals during the day. While growth rate of fish did not differ among treatments, that of crayfish was 31.5% higher in treatments where the feed was temporally separated, but only when the crayfish were small relative to the fish. Spatially separating the feed had no influence on growth of fish and crayfish of either relative size. Taken together, the results indicate that tilapia indirectly benefit from the presence of red claw over a wide range of sizes, probably by consuming some of the feed ration aimed for the crayfish. On the other hand, red claw are adversely affected mainly by larger fish. Feeding the crayfish during the night reduces this negative effect.

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