Fish oil (FO) and protein substitution by optimised levels of vegetable ingredients is one of the current strategies for reducing the cost of fish feeds and to reduce the dependency on fisheries to produce aquafeeds. We have previously shown that either fish meal or FO can be replaced by a mixture of vegetable oils (VO) up to 65-75% without growth retardation and sings of histo-pathological damage [1, 2]. Thus, the further step was to test whether these plant protein and VO optimised diets can alter the disease outcome in front of a pathogen challenge. The myxosporean Enteromyxum leei was chosen because it is widely spread in the Mediterranean basin and it is considered one of the most threatening parasitic diseases in Mediterranean fish cultures [3]. Naïve recipient (R) gilthead sea bream fed for 9 months either a FO-based diet or a diet in which FO was 66 % replaced by a mixture of vegetable oils (66VO) were challenged by exposure to E. leei-contaminated effluent coming from tanks holding parasitized fish. Control fish received the two different diets, but remained unexposed. Fish were individually pit-tagged and sampled non-lethally at different times post-exposure (p.e.) by probing the rectal portion, and the presence of the parasite was determined by PCR. Biometrical and feed intake data were also taken. After 102 days of exposure, fish were sacrificed and haematological, biometrical, histological (HIST), immunological (total peroxidases, complement, lysozyme, respiratory burst, NO) data, as well as antioxidant indexes (intestinal and hepatic glutathione levels and total plasma antioxidant capacity) were obtained from tissue, blood and serum samples. The disease outcome was higher in 66VO-R fish, since they showed a higher prevalence and mean intensity (MI) of infection, a higher percentage of fish harbouring the parasite in the entire intestinal tract, and a faster establishment of the parasite. Disease signs were also more pronounced in 66VO-R fish, since their growth, condition factor, specific growth rate and haematocrit were significantly decreased, and food intake was also reduced (20%). A global meta-analysis was performed to correlate the different obtained data.

Trabajo presentado en la 14th EAFP International Conference (European Association of Fish Pathologists), celebrada en Praga (República Checa), del 14 al 19 de septiembre de 2009