FOREGUT EVACUATION, RETURN OF APPETITE AND GASTRIC FLUID SECRETION INTHE TROPICAL FRESH-WATER CRAYFISH, CHERAX-QUADRICARINATUS

The effects of animal size and feeding frequency on the foregut evacua tion rates by Cherax quadricarinatus, that fed voluntarily on pellet f ood (meal size eaten, 1.3-1.4% body weight), were determined using a m odified serial slaughter method. Evacuation rates did not differ signi ficantly between size-groups (medium, large) and between feeding frequ ency-groups (fed daily, fed every second day). However, models that be st described the evacuation process were different for each group (i.e ., linear model for the crayfish fed daily, arcsine model for those fe d every second day). This variation indicates the potential for a cray fish to regulate its digestion processes according to food availabilit y. Faecal production rates did not differ significantly between feedin g frequencies. Return of appetite, measured in terms of voluntary feed intake at bi-hourly intervals following satiation meals, was shown to be related to the foregut evacuation process, but it was probably the supply of fresh gastric fluid after ca. 4 h following a meal which ma inly influenced the increase of appetite. The rapid return of appetite in crayfish implies that they can resume feeding while a considerable proportion of an earlier meal is still being processed in the foregut , This indicates that crayfish are capable of optimising the frequency of feeding during active foraging periods.