The ecology of some parasitic copepods of gadoids and other fishes

The migratory habits of Gadus merlangus and G. pollachius are examined n i relation to the variations in the rate of infection of these fish with Lernaeocera branchialis. A sudden increase in infection in estuarine and inshore waters is found to coincide with the offshore migration of the main stock. The infected fish apparently linger behind and may live for some time in the old habitats after the arrival of the next recruitment. The offshore migrants are seldom infected, and it is probable that infection does not take place in water deeper than about 5 fathoms. The possible immediate causes of this “lingering” phenomenon are examined, and two suggestions are made as to the nature of the physiological upset brought about by the presence of L. branchialis on these gadoids. Other factors influencing the distribution of the parasite are discussed. The relative susceptibility of the different species of gadoids to infection with species of Lernaeocera is examined as far as the data allow.

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