Review on the occurrence of caligids (Siphonostomatoida) in plankton samples of oceanic waters

Abstract

The genus Caligus M&uuml ller (Siphonostomatoida), well known as sea lice and belonging to the family Caligidae includes more than 250 species parasitizing marine fishes. Sea lice have a serious impact on cultured fishes around the world, but the increasing number of reports of their presence in plankton samples poses some interesting research questions. There have been several hypotheses concerning the occurrence of these parasitic copepods in the plankton. Such incidences have been regarded as 1) accidental occurrences, 2) behavioural detachment from the host in search for a suitable mate or 3) host-switching. In particular, the discovery of adults of Caligus chiastos Lin and Ho and C. sclerotinosus Roubal, Armitage et Rhode on farmed Thunnus maccoyii and Pagrus major, respectively, with no earlier developmental stages found on these hosts, suggested an ontogenic host-switching after the final molt. Adults of Caligidae particularly one widespread species, C. undulatus Shen and Li and Pandaridae (Pandarus Leach) have been reported repeatedly from marine plankton samples from different geographic regions. Recently, three different genera, Caligus, Lepeophtheirus von Nordmann, and Metacaligus Thomsen were reported from plankton samples including six new species whose hosts remain unknown? About 12 species without hosts have so far been reported from the plankton only. This alternative mode of life remains an intriguinut the increasing number of reports of their presence in plankton samples poses some interesting research questions. There have been several hypotheses concerning the occurrence of these parasitic copepods in the plankton. Such incidences have been regarded as 1) accidental occurrences, 2) behavioural detachment from the host in search for a suitable mate or 3) host-switching. In particular, the discovery of adults of Caligus chiastos Lin and Ho and C. sclerotinosus Roubal, Armitage et Rhode on farmed Thunnus maccoyii and Pagrus major, respectively, with no earlier developmental stages found on these hosts, suggested an ontogenic host-switching after the final molt. Adults of Caligidae particularly one widespread species, C. undulatus Shen and Li and Pandaridae (Pandarus Leach) have been reported repeatedly from marine plankton samples from different geographic regions. Recently, three different genera, Caligus, Lepeophtheirus von Nordmann, and Metacaligus Thomsen were reported from plankton samples including six new species whose hosts remain unknown? About 12 species without hosts have so far been reported from the plankton only. This alternative mode of life remains an intriguin