Effect of crowding stress on the immune response in turbot (Scophthalmus maximus) vaccinated with attenuated Edwardsiella tarda

The aim of this study was to evaluate the immune responses in turbot, Scophthalmus maximus, treated with 1 x 10(7) cfu/ml attenuated Edwardsiella tarda (0.1 ml/fish) under low density (LD; similar to 5.25-5.13 kg/m(2), initial to final density), medium density (MD; similar to 10.41-13.95 kg/m(2)), and high density (HD; similar to 20.53-30.77 kg/m(2)) conditions for 8 weeks. The results showed that there was a peak value in the percentage of sIg+ (surface immunoglobulin-positive) cells in blood leucocytes (BL), spleen leucocytes (SL), and pronephros leucocytes (PL) during the sixth week in the HD, which was delayed by week compared with the other groups. The specific immunoglobulin M (IgM) antibody levels increased from the first week in all groups and reached a peak in the fifth week in the LD and MD groups, but in the sixth week in the HD group. The serum cortisol levels were greater in the HD group compared with the other groups in the last 3 or 4 weeks. These results show that stocking turbot at a LD obtained the most effective immunization, and thus we conclude that crowding stress may reduce the ability to deal with immune challenge. (C) 2017 Elsevier Ltd. All rights reserved.