Effect of a functional feed additive on performance and parasite infection in gilthead seabream (Sparus aurata) challenged with Enteromyxum leei

Abstract

Enteromyxum leei is the causative agent of a parasitic emaciative disease (enteromyxosis) in multiple cultured marine fish species worldwide. In the Mediterranean, this parasite seriously hampers the production of sharpsnout sea bream (Diplodus puntazzo) or red porgy (Pagrus pagrus). The main economic impact on gilthead sea bream (GSB) aquaculture results from arrested growth and difficulties to reach commercial size of infected stocks, but epizootic outbreaks are not rare under some conditions. The lack of effective anti-parasitic therapies in Mediterranean aquaculture has stimulated the search for natural feed additives, which can be incorporated in functional feeds aiming at minimizing the impact of parasitic outbreaks on productivity. Empirical field evidence suggests certain efficacy on the mitigation of health problems including parasites such as E. leei of a functional feed additive (Sanacore® GM, Nutriad). These effects, however, are seldom validated in the laboratory. This work explores the effect of this functional feed additive on GSB enteromyxosis under controlled experimental laboratory conditions. Groups of GSB fed with additive - supplemented or control diets for 5 weeks were challenged with E. leei by anal intubation, and then maintained for 10 further weeks with the different diets. Data on food intake and fish growth were taken throughout the study. In the final sampling (10 wks post challenge), when fish fed the control diet showed the clinical signs of enteromyxosis, intestinal samples were taken for molecular and histological parasite diagnosis. The total parasite load per fish was calculated using a qPCR test targeting the E. leei rDNA gene. The anterior, middle and posterior intestinal segments were differentially examined in the histopathological study. Quantitative analyses of biometrical, growth performance, and parasite load of each group were conducted. The results showed significant differences between the additive-treated groups and the control group, in terms of increased growth performance and food intake, and decreased infection prevalence and parasite abundance. These results provide some experimental support for the consideration of preventive strategies using functional feeds to mitigate some chronic disease problems, although the mechanisms involved are not yet elucidated