Epidemiology of pseudodactylogyrosis in an intensive eel-culture system

Studies were performed on variations of prevalence and abundance in postlarvae and adults of the monogeneans Pseudodactylogyrus anguillae and P. bini from European eels in an intensive culture system.It appeared that a surge of settling parasite larvae always occurred after formaldehyde treatment of fish tanks, or after removal of bio-lilm from fish tank walls.Formaldehyde did not increase the susceptibility of eels to infection The absence of postlarvae for certain periods was not caused by resistance of eels, which could be affected by dexamethasone-treatment. Settling of oncomiracid~a was negatively correlated to activlty of freeliving organisms in the biofilm on the fish tank wall Laboratory tests showed that the biofilm-organ~sm Stenostomum sp.(Turbellaria) ingested Pseudodactylogyrus eggs.It is suggested that predatory act~vity of biofilm organisms influences the infection level, although other factors may be of importance.