Recovery of Third-Stage Larvae of Anguillicola Crassus (Nematoda : Dracunculoidea) From the Flesh of Fishes : Assessment of a Digestive Medium as a Tool for the Study of Fish Paratenic Hosts.

Abstract

The purpose of this study was to recover third-stage larvae (L3) of Anguillicola crassus alive from the flesh of fishes. Different digestive media have been tested on eel flesh for their efficiency and on living infective third-stage larvae for their harmlessness.The results were :(1) Long-term survival of the L3 larvae was low, but their morphological features were recognizable in each digestion runs.(2) Pepsin concentrations between 2.5 and 40 g/l proved to be without influence on the short-term (2-4 hours) survival of the L3 larvae of A. crassus. The digestion of the eel flesh was more advanced with the most concentrated media, when applied for 12 hours.(3) L3 larvae survived longer at pH 1.8 than 1.5, and digestion appeared to be faster at the upper pH level.(4) L3 larvae survival was much longer at 20°C than at 30°C, but efficiency of the digestion process was poor at the lower temperature.For epidemiological studies, the optimal factors combination has been established at pepsin concentration : 10 g/l, pH : 1.8 and temperature : 20-22°C, particularly when quantitative recovery of L3 larvae and work efficiency were taken into account. (1) La survie à long terme des larves L3 a été limitée, mais leur intégrité anatomique n'a pas été altérée, de sorte qu'elles sont restées identifiables dans chaque milieu testé. Key-words :(2) Aucune différence de survie à court terme (2-4 heures) n'a été constatée sur les larves selon la concentration en pepsine (2,5 ou 40 g/l). La concentration la plus élevée en pepsine a assuré une digestion plus poussée de la chair d'anguille après 12 heures de contact. Pour l'application pratique dans un contexte d'enquête épidémiologique, un compromis économique a du être trouvé entre, d'une part, une bonne digestion des chairs pour une récupération importante de larves L3 et, d'autre part, une bonne intégrité des larves afin de pouvoir les identifier. Les paramètres optimaux suivants sont préconisés : concentration en pepsine = 10 g/l ; pH = 1,8 ; température = 20-22°C.