Infection of hottentot Pachymetopon blochii by the fish louse Anilocra capensis (Crustacea: Isopoda) in False Bay, South Africa

Abstract

The frequency of occurrence, location on the host, abundance, and size and sex distributions of ectoparasitic isopods, Anilocra capensis, on hottentot  Pachymetopon blochii from False Bay, South Africa, were investigated. A. capensis occurred on 5.2 % of examined hosts and were usually attached above the  operculum, posterodorsally to the eye. They did not show any preference for a  specific sex of host, or side of the body. Parasites occurred most frequently in pairs (65.6 % of cases), or alone (32.8 %), with infection by more than two parasites rare (1.6 % of cases). The 604 P. blochii collected ranged in size from 13.0–50.9 cm, but parasitized individuals were only found amongst smaller size classes (14.8–31.2 cm), with only one individual larger than 28 cm parasitized. A. capensis individuals were found to be protandric hermaphrodites, passing through three stages (functional male, intermediate or ‘transitional’ stage, and then functional female) with increasing size. Parasite sizes were positively correlated with those of the host, suggesting that parasite and host growth could be concurrent. Length and weight of parasitized fish was slightly, but significantly below that of nonparasitized individuals, suggesting that infection by A. capensis had a negative effect on host
condition. Given the low frequency of infection by A. capensis within False Bay, however, it is unlikely that this has any significant adverse impacts on the hottentot fishery in the region.

Key words: Sparidae, ectoparasite, parasite location, parasite frequency.