Non-specific immune responses in the red porgy Pagrus pagrus after crowding stress

Red porgy (Pagrus pagrus) were exposed to crowding stress for 23 days. The responses measured were plasma glucose and cortisol concentrations, basic haematological variables and non-specific responses of the immune system: haemolytic activity of serum based on the alternative complement pathway (ACP), lysozyme and haemagglutinating activity of serum, total immunoglobulin concentration, and number of circulating lymphocytes. The results showed an initial moderate increase in cortisol followed by hyperglycaemia, and a further decrease of both variables over the following days. Immunodepression was apparent as shown by decreases in ACP levels and circulating lymphocytes after 2 days and haemagglutination titre after 9 days. Later samples showed a recovery of basal levels for lymphocyte numbers and haemagglutination titre and a significant increase of lysozyme levels after 16 days. Haemolytic levels did not recover at the end of the experiment. Results are discussed in view of the incidence of stress on indicative parameters of endocrine and immune systems in this species of recent interest for aquaculture.