FACTORS INFLUENCING POPULATIONS OF THE ECTOSYMBIONT DICERATOCEPHALA-BOSCHMAI (PLATYHELMINTHES, TEMNOCEPHALIDA), ON THE REDCLAW CRAYFISH CHERAX-QUADRICARINATUS MAINTAINED UNDER LABORATORY CONDITIONS

In commercial aquaculture, the redclaw crayfish, Cherax quadricarinatu s can harbour very large numbers of the temnocephalid ectosymbiont, Di ceratocephala boschmai, Such heavy infestations could not be replicate d in the laboratory where worm populations increased to reach a maximu m of less than 30 worms. Numbers of D. boschmai are not limited by pre dation by a second temnocephalid Decadidymis gulosus and there was no evidence of cannibalism. The crayfish grooming response was the most i mportant factor controlling population size in Diceratocephala boschma i. Crayfish groom themselves with their walking legs; chelipeds 2 and 3, and pereopods 4 and 5. In the laboratory, redclaw with four of thes e cleaning limbs ablated, developed significantly greater infestations with temnocephalids than did crayfish with all appendages intact. Hos t ecdysis also influenced the population dynamics of the worm; populat ions decreased by 50% (range 25-80%). Worms did not actively attempt t o gain access to the new carapace although those worms found at the ba se of the walking legs did so most successfully.