HOST SPECIFICITY OF LEPEOPHTHEIRUS-PECTORALIS (MULLER, 1776) (COPEPODA-CALIGIDAE)

The host specificity of L. pectoralis was examined experimentally by exposing different fish species to infection by artificially reared copepodid larvae. Copepodids hatched from eggs of adults parasitic on plaice Pleuronectes platesia (platessae copepodids) preferred plaice to all other fishes tested; copepodids hatched from eggs of adults parasitic on flounder Platichthys flesus (flesi copepodids) preferred flounder to all other fish species. These behavioral differences suggest that 2 strains of L. pectoralis exist, one (platessae) adapted to plaice as its host and the other (flesi) to flounder. Comparison of an experimentally derived order of host preference with a table of occurrence from the literature suggests that a 3rd strain of L. pectoralis, adapted to dab Limanda limanda as its host, might also occur. The process of infection by L. pectoralis copepodids is described. It comprises a host location phase, during which the copepodid enters the habitat of its flatfish hosts and locates a host individual, and an attachment phase. The host location phase appears to be governed by changes in the activity of the copepodid and by its positively rheotactic response to water currents produced by the host. The attachment phase is probably based on the response of the copepodid to chemical factors produced by the host.