AQUACULTURE AND ICHTHYOPARASITOLOGY - IN- VITRO ACTION OF NITROXINIL (ANTHELMINTIC) DIPLECTANUM AEQUANS, GILL ECTOPARASITE OF THE SEA BASS DICENTRARCHUS-LABRAX

The sea bass Dicentrarchus labrax is subject to intensive rearing. Sev eral monogeneans, gill ectoparasites with a direct biological cycle, p arasitized this Teleostei. Under certain conditions of host density, p opulations of these pIatyhelminths can increase and consequently induc e important mortality. It's especially the case of Diplectanum aequans , a monopisthocotylea against which no treatment is known. in vine eff ects of nitroxinil (or nitroxynil), an anthelmintic, were investigated . Parasites were exposed to different concentrations bounded by 50 and 2 000 mg.l(-1). Each Diplectanum has been submitted to a treatment du ring four hours, and successively displayed different behaviours. It c an lose its spontaneous mobility, react or not to mechanical stimuli a nd/or get unhooked. These behavioural variations were analysed in func tion of time and concentrations.