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A comparative study was conducted of blood chemistry and histopathology of Nile tilapia (Oreochromis niloticus) after infection with Vibrio vulnificus or Streptococcus iniae or exposure to carbon tetrachloride (CT), gentamicin (Gm), or copper sulfate (Cu). Treatments were chosen as models targeting different organs and from which different types of lesions were expected. Moderate histological changes were observed in the gill, trunk kidney, liver, spleen, and head kidney in both bacterial infections. Gentamicin induced significant changes in the trunk kidney, liver, and intestine, while carbon tetrachloride treatment caused changes in the liver and trunk kidney. Copper treatment only caused mild proliferation of the gill epithelium.Among the blood chemistry parameters measured, hematocrit, iron, glucose, sodium, and chloride were good indicators of deteriorating health in tilapia, with significant changes in those parameters being observed in most treatment groups. Severity of histopathology in the liver, intestine, and trunk kidney was associated positively with alanine aminotransferase (ALT) and aspartate aminotransferase (AST) but negatively with sodium, chloride, cholesterol, and total protein. Anion gap was the only blood chemistry parameter correlating to histopathology in the spleen and head kidney. Standardized principal component analysis, discriminant analysis, and canonical correlation analysis were applied to the blood chemistry and histopathology data. A consensus set of important parameters that included sodium, chloride, bicarbonate, total protein, ALT, AST, cholesterol, total iron binding capacity, and iron was obtained. Using a 7-parameter model that included potassium, ALT, iron, total protein, bicarbonate, creatine kinase, and AST, 70% of the fish could be correctly classified to the appropriate treatment group, while a 17-parameter model allowed 81% proper classification. [Copyright &y& Elsevier]

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. [Copyright &y& Elsevier]