Comparative study of biochemical and nonspecific immunological parameters in two tilapia species (Oreochromis aureus and O-mossambicus)

Oreochromis aureus and O. mossambicus were compared in a preliminary study of differences in levels of blood biochemical and nonspecific immunological parameters before and after exposure to acute stress, which was induced by air exposure for 10 min. Two experiments were conducted. In the first experiment comparisons were performed after two weeks of acclimation ("base-line" level), after stress, and for stress response. The latter was calculated for each fish by subtracting the level after stress exposure from the base-line level. Significant differences (p<0.01) were identified between species at the base-line level in total plasma cholesterol and total protein levels. Glucose concentration was significantly different after stress and in stress response. Significant differences between species were also identified in respiratory burst activity of phagocytes after stress and in ceruloplasmin activity after stress. No significant correlation was identified between body weight and each of the parameters tested, indicating that the differences detected in immunological parameters were not related to the notable size difference between the two groups used in this study. The significant differences in total cholesterol and protein were confirmed in the second experiment. Significant differences (p<0.05) were also detected in levels of albumin, globulin, lactate dehydrogenase, calcium, total bilirubin and triglycirides, which were measured by autoanalyzer, and in alpha, beta 2, and IgM globulins, %beta1 and %IgM, which were separated and measured by agarose gel electrophoresis. Wide variation was detected within O. aureus in some of the parameters examined. A larger sample size should be used to learn if the differences are large enough to produce segregating O. aureus families for genetic analysis of those parameters. The differences identified suggest that hybrid families from the two species can be used to construct a segregating population for genetic analysis of immunological traits and stress response in tilapia.