Some aspects of the biology of the plerocercoid of Gilquinia squali Fabricius 1794 (Cestoda: Trypanorhyncha)

The eyes of more than 24 000 northern North Sea whiting were examined for infection with Gilquinia squali plerocercoids. Infection, which is apparently non‐seasonal, begins when the fish are aged 1 +, builds up to a peak at 2+ to 4+, and decreases thereafter. The intensity of infection ranged from 1–18 plerocercoids per fish. Evidence is presented of the development of immunity in whiting to G. squali, and observations on the parasite's eggs suggests that they are not randomly distributed but tend to aggregate. One or both of these features could give rise to the negative binomial type of frequency distribution observed. The frequency of left eye infection was consistently greater than that of right eye.