Aspects of the biology of the plerocercoid of Grillotia erinaceus (van Beneden, 1858) (Cestoda: Trypanorhyncha) in haddock Melanogrammus aeglefinus (L.)

From one to thirty Grillotia erinaceus plerocercoids were found in 3714 of 8228 haddock Melanogrammus aeglefinus caught in the northern North Sea, to the north and west of Scotland and at Faroe. Plerocercoids were also found in 30 of 64 cod from Aberdeen Bay, and in 44 of 55 saithe from the Firth of Clyde. In haddock, most plerocercoids occurred encysted along the intestine, and their frequency fitted a negative binomial distribution. Incidence and intensity of infestation increased with host age and there was no host sex difference in incidence. Three maturity stages were recognized, the proportions of which were consistent between haddock length groups. No precipitin bands developed in gel diffusion tests using live plerocercoids and sera from infested and uninfested haddock. Attempts to transfer plerocercoids between haddock were unsuccessful. Speculations are made on the possible course of the life-cycle.