Effects of azithromycin on tilapia (Oreochromis niloticus): health status evaluation using biochemical, physiological and morphological biomarkers

Bacterial diseases cause tilapia's high-mortality outbreak. This study investigated the toxicity of azithromycin (AZT), a macrolide antibiotic that has been considered a possible therapeutic drug for tilapia aquacultural use. The 48-h acute toxicity (50% lethal concentration, LC50; 48h) of AZT was determined for Oreochromis niloticus. Thereafter, fish were exposed to 0, 1, 50 and 100mgL(-1) AZT during 14days (chronic exposure) and measured the haematological variables, the activity of superoxide dismutase, catalase, glutathione peroxidase, glutathione-S-transferase (GST) and the concentration of glutathione (GSH), protein carbonyl and lipid peroxidation in the liver; histopathology was analysed the liver, gills and kidneys. The LC50; 48h was >100mgL(-1). No fish died during chronic exposure. Haematocrit and haemoglobin concentration increased in fish exposed to 50 and 100mgL(-1), and the total number of leucocyte and thrombocyte increased after exposure to 100mgL(-1) AZT, suggesting a stimulation of defence cell production. In the liver, the antioxidant enzyme activities did not change, but GST activity and the GSH level increased in fish exposed to 100mgL(-1) AZT. Oxidative stress did not occur. Histopathological index (HIL) indicates moderate liver damage; minor histological changes in the gill and no change in the kidneys. AZT was considered non-toxic for O. niloticus after acute exposure and, although it causes moderated histopathology in the liver after chronic exposure, this antibiotic may be an alternative against bacterial infections, depending on its efficacy to control bacterial disease in fish.