Dietary influences of oxytetracycline on the growth and serum biomarkers of Oreochromis niloticus (L.)

Tilapias are cultured globally and are rising in acceptance as the most important freshwater aquaculture species. Monitoring of serum biomarkers is a promising tool in aquaculture to screen the health status as they are virtuous indicators of extreme stress and organ dysfunction in fish. The present study examined the serum biomarkers of oxytetracycline (OTC)-dosed Nile tilapia Oreochromis niloticus at 0, 80 and 800 mg/kg biomass/day, i.e., OX, 1x, and 10X the approved dose (X = 80 mg OTC/kg biomass/day) for 10 consecutive days. The fish biomass and levels of serum glucose, aspartate aminotransferase, alanine aminotransferase, creatinine and C-reactive protein (CRP) were determined at scheduled intervals. A significant dose-dependent reduction in fish biomass during the OTC-dosing (5.84%) and post-OTC dosing (8.16%) periods was observed. All the serum biomarkers of Nile tilapia increased significantly on day 10 OTC-dosing. Though their levels reduced significantly, normalcy was not achieved even after 42 days of cessation of OTC-dosing, except CRP. The CRP reached the normal level on day 25 post-OTC dosing in the 1x group. The results, thus, demonstrated that the oral OTC-dosing influences the physiological state of apparently healthy Nile tilapia in a dose-dependent manner. These changes were, however, reversible upon discontinuation of OTC-dosing. The set of data observed on growth reduction and elevated serum biomarker levels even after 42 days of cessation of OTC-dosing, thus, raises questions on the utility of oral OTC-dosing.