EFFECTIVENESS OF FORMALIN, BENZOCAINE, AND HYPOSALINE AND HYPERSALINE EXPOSURES AGAINST ADULTS AND EGGS OF ENTOBDELLA-HIPPOGLOSSI (MULLER), AN ECTOPARASITE ON ATLANTIC HALIBUT (HIPPOGLOSSUS-HIPPOGLOSSUS L) - LABORATORY STUDIES

Treatments against E. hippoglossi, both adults and eggs, were investigated under laboratory conditions. Adult E. hippoglossi were transferred from the skin of halibut to glass vessels containing formalin (200 ppm), benzocaine (80 ppm), and water of different salinities, where the effectiveness of the different treatments was based on time to detachment. The adult parasites were tolerant to formalin, detached rapidly in benzocaine and were effectively killed by hypersaline and freshwater exposures. The eggs of E. hippoglossi were exposed to freshwater, hot (50-degrees-C) freshwater, and formalin (500 ppm) at three different stages in the incubation period (days 6, 14 and 35). A prolonged freshwater exposure from 10 min to 2 h resulted in a successively reduced hatching success to less than 20%. Hatching success was significantly higher at day 35 than at day 6 when freshwater treatment ranged from 10 min to 1 h. Treatment with hot freshwater (50-degrees-C) for 5 min at all three stages in the incubation period resulted in < 20% hatching success. Formalin treatment of the eggs at day 6 resulted in < 10% hatching success, but identical treatments at day 14 and 35 resulted in significantly higher hatching success.