Effect of long-term oral administration of an immunostimulant diet on innate immunity in sea bass (Dicentrarchus labrax)

Immunostimulants represent a modern and promising tool in aquaculture, enha ncing the resistance of cultured fish to disease and stress. This study inv estigated the effect of a combination of dietary glucans, alpha -tocopherol and ascorbic acid on the innate immune response of cultured sea bass (Dice ntrarchus labrax). After 5 weeks of adaptation on a commercial diet contain ing 100 p.p.m. ascorbic acid and 200 p.p.m. alpha -tocopherol, sea bass wer e switched to a diet supplemented with 2% beta -1.3/beta -1.6 glucans and a scorbic acid and alpha -tocopherol at 500 p.p.m. The supplemented diet was given at 2% of body weight per day over a 2-week period, every 3 months. Pl asma lysozyme concentration, content and distribution of major plasma prote ins and complement activity were measured prior to heeding the supplemented diet and after 40 weeks, Alternative pathways of complement activation and lysozyme activity were both significantly enhanced in fish fed on glucans and elevated doses of vitamins. No significant differences were observed in protein content or in albumin/globulin ratio. Compared to lysozyme activit y, which showed marked individual variation, complement-mediated haemolytic activity has been shown to be a more reliable indicator of sea bass immuno competence. Further studies are in progress to clarify the effect of each d ietary component on the innate immune response and disease resistance.