In vitro treatments of deltamethrin against the isopod parasite Anilocra physodes, a pathogen of seabass Dicentrarchus labrax L

The in vitro efficacy of the pyrethroid deltamethrin against the isopod parasite Anilocra physodes was determined under laboratory conditions. The following concentrations of the drug were tested on adult and pre-adult parasites by means of bath treatments of half an hour duration: 10mg/L, 1mg/L, 3mg/L, 0.3mg/L, 0.1mg/L, 0.01mg/L, 0.05mg/L, 10μg/L, 5μg/L, 0.15μg/L, 0.1μg/L. Results were assessed after 30 minutes, 2, 12, 24 and 48 hrs. The best concentration was proved to be 0.05mg/L where all parasites died at 2 hours and remained dead for 48 hrs. Introduction Recently, copepod and isopod infestations have been reported in cultured marine fish in the Mediterranean region (Athanassopoulou et al., in press). High moralities have been recorded due to the isopod parasite Anilocra physodes and to a lesser extent, the copepods Caligus spp and Lernanthropus kroyeri in juvenile cage-reared sea bass and sea bream Sparus aurata (Theohari, Ragias & Bai, 1997). However, it is Anilocra physodes and Ceratothea oestroides that have become the major parasite problem for young sea bass reared in cages in the Aegean Sea (Sarusic, 1999).. The parasite is found in the mouth, the skin and branchial cavity of a number of marine fish. Adult parasites most commonly are seen in pairs in the buccal cavity the male being smaller than female. After copulation, pullus larvae are hatched in the marsipium of the female parasites and released to the environment where they undergo several metamorphosis stages. It is the second stage (pulli II) that is believed to attack the cultured fish and the stage that causes most problems (Lindsay and Moran, 1976). These pulli II show low specificity in terms of attachment location on the host in contrast to the adult stages that normally attach to the buccal epithelium and cause less damage. In the latter case lesions are caused by the copulation activity or due to their size (atrophy of the tongue and dysplasia of teeth) resulting in poor growth of the