Locomotory rhythms and burrowing habits of Penaeus semisulcatus (de Haan) and P. Monodon (Fabricius) (Crustacea: Penaeidae)

The locomotor activity of adult Penaeus semisulcatus (de Haan) and P. monodon (Fabricius) has been studied. The former was reared entirely, and the latter partly under artificial conditions. Both species display circadian activity rhythms in response to light entrainment. Light appears to be a major synchronizer, although the results indicate that feeding also has a certain synchronizing effect in starved prawns.The expression of endogenous activity rhythms in both species is affected by their substratum requirements and burrowing habits. Choice experiments show that both P. semisulcatus and P. monodon select a fine grade sand for burrowing, although the burrowing frequency of the latter species is always low. In a non-choice situation, P. semisulcatus will readily enter a coarse substratum whereas P. monodon will very seldom do so.The effects of various light regimes on the activity patterns of P. semisulcatus and P. monodon were examined and the results show that for both species an imposed long photoperiod regime (18:6 LD) induced 6-h periods of brief but intense activity, alternating with 18-h periods of almost complete inactivity. This activity pattern is discussed in relation to feeding and energy expenditure.