Acanthocephala worms in intensively bred fish of Oncorhynchus mykiss.

In the last decades aquaculture become more and more important in the production of fish in Italy. In intensively breeding fish parasitic infections are considered to be an emerging economic problem. Acanthocephala are important parasites of the sylvatic and extensively bred fish because of their high prevalence and of pathological alterations due to the penetration of their presoma through the host’s intestinal wall. However little informations are available on these parasites in intensively bred. Aim of this research was to report the results of a study performed in Central Italy in two great intensively bred of rainbow trout conducted with different management with regard to parametres as hygiene, density of fish population, temperature, water supplying. During late spring (2001) were examined a total of 240 rainbow trout, mean lenght 30-32 cm. (n. 120 from each bred). In bred n. 1 the observation of the entire intestine gave these results: a prevalence of acanthocephalans of 60%; mean parasites/fish ± SD=93 41; mean weight positive fish ± SD= 318 ±34; mean weight negative fish ± SD= 340 ±29. In bred n.2 the results showed: a prevalence of 45% ; mean parasites/fish ± SD=84 ±37; weight positive fish ± SD= 286 ±63; mean weight negative fish ± SD= 380 ±47. This last difference in weight was statistically significative (*P < 0.05). Echinorhynchus truttae was the parasite present with higher prevalence in both bred (ranged from 90 to 94%); few parasites of the species Pomphorhynchus laevis were observed. The results confirm the different effect of a similar parasitic burden on the same species of fish. The importance of other biological and not biological factors influencing the pathogenicity (intensity and periodicity of light, water temperature, chemical and biological characteristics of water, availability of food and space) must be considered.