Spatial distribution of Nemesis lamna Risso 1826 (Copepoda: Siphonostomatoida: Eudactylinidae) on the gills of white sharks Carcharodon carcharias off KwaZulu-Natal, South Africa

Abstract

The selection of a specific site of attachment by a copepod parasite is determined by a set of mostly unknown factors. The spatial distribution of Nemesis lamna on the gill filaments of white sharks Carcharodon carcharias was investigated. The complete set of left gills of 11 hosts was examined and the location, orientation and gender of each copepod noted. N. lamna exhibited a prevalent of 100% and a mean intensity of 74 individuals per shark. There was no relationship between the size of the host and the number of filaments per hemibranch or the number of N. lamna attached to the host. Only 13.7% of the variation in number of individuals per hemibranch was due to the variation in the number of filaments per hemibranch, and most specimens (33.6%) were collected from the fourth holobranch. Most N. lamna (86.5%) were attached to the dorsal and ventral quarters of the hemibranchs, of which 63.1% were attached to the outer hemibranchs. There was no site preference in terms of their position on the filaments, but most were attached with their cephalothoraces facing the incoming respiratory water flow, especially those attached to the proximal quarter. The N. lamna infrapopulations on white sharks are aggregated, which is probably due to the need to reproduce.