ABSTRACT: A parasitic isopod, Livoneca sp. (Flabellifera: Cymothoidae), is reported from silverside Atherinomorus lacunosus in the Red Sea. The female isopod settles on the fish's tongue. Presence of a gravid female in the oral cavity was always associated with that of a single, smaller male occupying the gill chamber. Approximately 3.6% of the fish examined were found to be infested with the parasites in the adult phase. Histological damage to the fish appears limited to the gill rakers and filaments upon which the female isopod rests her abdomen and tail. The gill filaments above the site in which the male settles become similarly dystrophic. However, none of the fish infested displayed any obvious sign of respiratory distress or stunted growth. The chitinous segments of the isopod armoring, imbricated like roof tiles with their free margin directed backward, seem perfectly adapted to performing the same gripping function as the fish's tongue. This host-parasite relationship appears to be species-specific and has all the characteristics of an evolutionary process of adaptive strategy, as it clearly enables the host to maintain its feeding ability while the parasite grows to sexual maturity.

KEY WORDS: Cymothoid · Isopod · Parasite · Livoneca · Silverside · Atherinomorus lacunosus · Atherinidae · Red Sea

Published in DAO Vol. 31, No. 1 (1997) on October 28
ISSN: 0177-5103. Copyright © Inter-Research, Oldendorf/Luhe, 1997