Social control of growth in the redclaw crayfish, Cherax quadricarinatus: testing the sensory modalities involved

The magnitude of and the sensory involvement in social control of growth in Cherax quadricarinatus were analyzed in the laboratory. In the first experiment 80 pairs of juvenile males, each comprising a relatively small (2.0 g) and a relatively large (3.5 g) crayfish, were raised for 66 days under six different types of social contact. The pairs were raised in full contact with either intact or immobilized claws, separated by a partition with the allowance of transmission of chemical and/or optical cues, and without any contact. Any type of contact with the small one did not affect the growth of the large individual. However, the growth of the small individual was reduced by 50% only when in full contact with the large one, because of both increased time between successive molts and a reduction in the size increment per molt. In the second experiment small juvenile males were reared for 98 days in chemical and/or optical contact with much larger adult males. As in experiment 1, no effect of the chemical and/or optical cues on growth was found. The relevance of these findings to C. quaricarinatus culture is discussed.