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 quadricarinatus can harbour very large numbers of the temnocephalid ectosymbiont, Diceratocephala boschmai. Such heavy infestations could not be replicated in the laboratory where worm populations increased to reach a maximum of less than 30 worms. Numbers of D. boschmai are not limited by predation by a second temnocephalid Decadidymis gulosus and there was no evidence of cannibalism. The crayfish grooming response was the most important factor controlling population size in Diceratocephala boschmai. Crayfish groom themselves with their walking legs; chelipeds 2 and 3, and pereopods 4 and 5. In the laboratory, redclaw with four of these cleaning limbs ablated, developed significantly greater infestations with temnocephalids than did crayfish with all appendages intact. Host ecdysis also influenced the population dynamics of the worm; populations decreased by 50% (range 25–80%). Worms did not actively attempt to gain access to the new carapace although those worms found at the base of the walking legs did so most successfully.