engleski

Histopathological alterations induced by gill and skin parasitic infections in the Atlantic bluefin tuna (Thunnus thynnus) and its innate response modelled in vitro

For the farming purposes, juvenile Atlantic bluefin tuna (ABT) Thunnus thynnus are fished in the South Adriatic and transferred into farming cages, introducing along an abundant and diverse parasite community. Throughout the farming process, it was observed that most parasites taxa decrease, not constituting a serious economic threat for the aquaculture. Didymozoid trematode Didymosulcus katsuwonicola and siphonostomatoid copepods Pseudocycnus appendiculatus and Brachiella thynni, are all gill/ skin parasites frequently parasitizing tuna, whose populations conspicuously decline during the farming cycle. In order to shed the light on the immunity mechanisms underlying Atlantic bluefin tuna reaction to these three species, we studied expression profiles of three major cytokines ; IL-1β, TNFα1 and TNFα2 in peripheral blood leukocytes (PBL) during in vitro stimulation by didymozoid and siphonostomatoids antigens. As an additional record to support molecular results of the later scenario, a pathohistological analysis of parasitic infections was performed on semi- and ultrathin sections of infected gill filaments. Resulting induction of the Atlantic bluefin tuna pro-inflammatory cytokines IL-1β and TNFα2 by parasite-derived antigens was evidenced, while cellular response inferred by TEM differed in respect to parasite species. Cellular innate response to the digenean showed rather chronic character, resulting with parasite encapsulation in connective tissue, and mast cells, eosinophils, goblet cells, and occasional rodlet cells found at the site of infection. In contrast, copepods attached to the gill/ skin epithelium by clamping, caused direct tissue disruption with undergoing necrotic or apoptotic processes, and extensive proliferation of rodlet and goblet cells. In all cases, it seems that the presence of moderate inflammatory reaction fails to seriously endanger parasites existence, and that other factors should be relevant in its decrease.

Didymosulcus katsuwonicola; Pseudocycnus appendiculatus; Brachiella thynni; cytokines

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