Effects of oxytetracycline exposure in Oncorhynchus mykiss: oxidative defence system, peroxidative damage and neurotoxicity

In recent years, the presence and effects of pharmaceutical drugs in aquatic ecosystems has received increasing attention from the scientific community. The increasing use of pharmaceutical drugs, such as antibiotics, is cause of concern due to their potential biochemical and physiological deleterious effects. Antibiotics are particularly important because they include a variety of substances widely used in medical and veterinary practice, livestock production and aquaculture. These compounds, such as oxytetracycline (OXY), may act not only on cultured organisms, but also in non-target species. OXY is tetracycline, being used worldwide in aquacultures, due to its high efficacy against bacterial diseases (e.g. vibriosis, enteric redmouth, and also furunculosis). The present study aimed to assess the toxic effects of OXY in the freshwater fish Oncorhynchus mykiss. Fish were exposed during 96 h to OXY in concentrations of 0.005, 0.050, 0.500, 5.00 and 50.0 mg/L. In order to evaluate OXY effects in the rainbow trout, biochemical markers were analyzed, include those focused on oxidative stress parameters [catalase (CAT), total glutathione peroxidase (GPx), glutathione reductase (GRed), and glutathione-S-transferases (GSTs) activities); lipid peroxidation levels (TBARS levels), in liver and gills]; and neurotransmission, (acetylcholinesterase AChE, in muscle and eyes). The here-obtained data showed the occurrence of oxidative stress, reflected by an increased activity of GPx, GRed and GSTs (in gills) and increase of TBARS levels in liver. Additionally, it was possible to observe significant alterations in AChE activities, with decreases in the eyes and increases in muscle. Short-term effects of antibiotics were observed indicating that physiological impairment in fish may occur, with the involvement of multiple organs and biochemical pathways. The global significance of the entire set of results is discussed, giving emphasis to the ecological relevance of the responses.