Abstract

The influence of a nucleotide-enriched diet on the immune system, plasma cortisol levels and resistance to infectious pancreatic necrosis (IPN) was evaluated in infected juvenile rainbow trout. Non-infected fish were sampled monthly and subgroups injected with the IPN virus (IPNV) at days 60 and 120 after feeding trial onset were sampled one week after injection. Immune responsiveness was assessed by mitogen-induced lymphocyte polyclonal expansion; stress levels were measured by plasma cortisol levels using radio-immuno-assay (RIA) and pathogen presence by reverse transcription (RT) polymerase chain reaction (PCR). Non-infected trout, fed with the nucleotide diet, showed higher stimulation indexes of both "B" and "T" lymphocytes after 3 months and normal plasma cortisol levels. Results in trout infected with IPNV, indicate that the nucleotide diet was able to: a) stimulate only "B" lymphocytes and b) decrease plasma cortisol levels. All IPNV-injected and normal diet fed trout died after one week, whereas all the fish in the nucleotide enriched diet subgroup survived. All non-infected fish survived in both normal and enriched diet subgroups. It can be concluded that a nucleotide-enriched diet supplied prior to IPNV infections, is able to stimulate the humoral immune response and decrease elevated stress levels, probably caused by the disease.