Blood chemistry of healthy, nephrocalcinosis-affected and ozone-treated tilapia in a recirculation system, with application of discriminant analysis

Blood chemistry parameters of Nile tilapia (pure strain Oreochromis niloticus) raised in a recirculation system were studied. Plasma samples were collected from 30 healthy tilapia every 3 months during a 1-year period. An additional 30 tilapia affected with nephrocalcinosis, and 30 fish from a system treated with ozone were also examined. Significant differences among healthy groups were observed in all parameters except for plasma magnesium, iron, albumin-to-globulin ratio, glucose, cholesterol, and alanine aminotransferase (ALT), aspartate aminotransferase (AST), alkaline phosphotase (AP) and creatine kinase (CK) activities. Nephrocalcinosis-affected tilapia differed significantly from healthy fish in most electrolyte and metabolite concentrations, as well as in ALT, AST and AP activities. Ozone-treated fish showed significant differences in electrolyte concentrations and ALT, AST and AP activities. Discriminant analysis revealed good separation of these groups. Evaluation of the data set indicated that the number of blood chemistry parameters could be reduced from 23 to 9 without losing the ability to separate the groups (90% and 92% correct, respectively). Most of the incorrect prediction came from less satisfactory separation of ozone-treated fish from healthy fish, due to the lack of apparent adverse impact on health of this treatment. Thirty tilapia from the same facility that were experiencing a low mortality rate were also used to test the model; individuals with abnormal blood chemistry profiles were identified.