Dietary administration of β-1,3/1,6-glucan and probiotic strain Shewanella putrefaciens, single or combined, on gilthead seabream growth, immune responses and gene expression.

It is widely known that β-glucans and probiotic bacteria are good immunostimulants for fish. In the present work we have evaluated the dietary effect of β-1,3/1,6-glucan (isolated from Laminarina digitata) and Pdp 11 (Shewanella putrefaciens, probiotic isolated from gilthead seabream skin), single or combined, on growth, humoural (seric level of total IgM antibodies and peroxidase and antiprotease activities) and cellular innate immune response (peroxidase and phagocytic activities of head-kidney leucocytes), as well as the expression of immune-related genes in gilthead seabream (Sparus aurata). Four treatment groups were established: control (non-supplemented diet), Pdp 11 (10(9) cfu g(-1)), β-1,3/1,6-glucan (0.1%) and β-1,3/1,6-glucan + Pdp 11 (0.1% and 10(9) cfu g(-1), respectively). Fish were sampled after 1, 2 and 4 weeks of feeding. Interestingly, all supplemented diets produced increments in the seabream growth rates, mainly the Pdp 11-suplemented diet. Overall, Pdp 11 dietary administration resulted in decreased serum IgM levels and peroxidase activity. However, the seric antiprotease activity was increased in fish fed with both supplements together. Furthermore, β-1,3/1,6-glucan and combined diet increased phagocytic activity after 2 or 4 weeks. At gene level, IL-1β and INFγ transcripts were always up-regulated in HK but only the interleukin reached significance after 4 weeks in the group fed with β-glucan. On the contrary, IgM gene expression tended to be down-regulated being significant after 1 week in seabream specimens fed with β-glucan or β-glucan plus Pdp 11. These results suggest that β-1,3/1,6-glucan and Pdp 11 modulate the immune response and stimulates growth of the gilthead seabream, one of the species with the highest rate of production in Mediterranean aquaculture.