Parasitological study of a population of Tiber River eels (Anguilla anguilla).

A study was conducted on the parasitofauna of Anguilla anguilla caught in the section of the Tiber river south of Rome (Italy). The sample examined consisted of 417 specimens that were classified by stage (elver, young yellow eel, yellow eel and silver eel) and season of sampling. The following species were identified: Trypanosoma granulosum, Eimeria anguillae, Myxidium giardi, Sphaerospora reichenowi, Myxobolus sp., Trichodina anguilli, Ichthyohodo sp., Gyrodactylus anguillae, Bothriocephalus claviceps, Proteocephalus macrocephalus, Raphidascaris acus, Acanthocephalus clavula. Each parasite species was considered in its prevalence according to stage and season. For some parasite the pathogenic effect was also examined in a histological study of serial sections. The results of the statistical analysis of the single parasitic infection as related to different seasons pointed to marked seasonal trends only in some species (Trypanosoma granulosum and Gyrodactylus anguillae). The intensity of infection assessed for acanthocephalan infection only was found to affect neither weight nor condition index (weight/length3). No difference in weight or condition index was found to be ascribable to the presence or absence of a species. An attempt to find a rule-of-thumb algorithm to gauge the overall effect to parasitic diseases failed to give sufficiently significant results.