Immunostimulation of juvenile turbot (Scophthalmusmaximus L.) using an alginate with high mannuronic acid content administered via the live food organism Artemia

The effect of crowding condition (25g 1−1) on the non-specific immune response of fancy carp (Cyprinus carpio L.) was studied. The fish were stressed for 1, 7, 14 and 30 days. The total serum protein concentration, serum lysozyme activity, bactericidal complement activity and chemiluminescent (CL) response of the phagocytic pronephros cells were all measured on day 30 after the initial crowding stress. Their susceptibility to infectious disease was tested by challenging with the bacterium Aeromonas hydrophila. Stress indicators such as plasma cortisol, glucose and chloride levels were also determined. The results indicated that the levels of cortisol and glucose were significantly increased from day 1 onwards until day 30. On the other hand, the activities of non-specific immune parameters except for phagocytic activity significantly dropped on day 1, and then remained low throughout the remaining time intervals. Disease resistance of the stressed fish was significantly reduced on day 7. However, no great difference in resistance against A. hydrophila was found between day 7 and day 30. No mortality was encountered in either stressed or unstressed fish. This indicates that fish might have an adaptation capability to survive under a stable, chronically stressful environment although the activities of non-specific defence mechanisms were significantly lower than those of the unstressed fish.