Design of a stress model in the hybrid bass (Morone saxatilis x Morone chrysops)

The effects of different stress-causing agents such as hypoxia, temperature shift, netting, bleeding and air exposure, as monitored by measuring blood glucose alterations, were determined in hybrid bass (Morone saxatilis x M. chrysops). Results obtained using a multifactorial stress model (netting, bleeding and air exposure) showed that elevation of blood glucose was linea rly correlated with progressive stress intensity. By using a simpler labora tory model based on air exposure only, it was shown that bleeding at the be ginning of the experiment had no significant effect on final glucose levels measured after 7 hours. The maximal blood glucose level in all stress proc edures ranged 326-392 mg/dl. The higher values were followed by severe sign s of stress and even mortality. Hypoxic water caused rapid stress, with 326 mg/dl blood glucose in only 90 minutes. Conversely, a slowly developing st ress response was achieved by abruptly lowering the temperature by 7 degree s C. The air exposure model was also used for testing lysozyme activity dur ing stress. Contrary to glucose, plasma lysozyme was significantly lower in stressed than in unstressed fish. While no significant differences were ev ident in lymphoid tissues at 7 h, lysozyme activity increased significantly after 24 h in the spleen and posterior kidney, but not in the anterior kid ney. A possible explanation of this phenomenon is discussed.