Abstract

From economic and sanitary points of view, diseases are considered the most limiting factor in salmon production. The most frequently used antibiotic drug in Chile is florfenicol, followed by oxytetracycline (OTC). But these antibiotics, like any commercial pharmaceutical drug, have many side effects. Side effects of antibiotics have been described in fish, associated with antioxidant and behavioral responses, but there are few antecedents in farmed fish, using recommended doses for treatment and at different post-treatment times. In this work, the effects of OTC on serotonergic response in the telencephalon and hypothalamus of Coho salmon (Oncorhynchus kisutch), were investigated following the administration in vivo (i.p. injections) and brain tissue culture (in vitro) of regular doses used of OTC at different times. Serotonin (5HT) levels were significantly affected, both in vivo and in vitro experiments, by both doses of OTC, showing in general a decrease in serotonin levels in the first hours and days of treatment, but at day 5 post-treatment, levels are similar to the control group. The qRT-PCR expression levels of the genes associated with the serotonergic system (TPH1, TPH2, SERT, 5HT1A alpha, 5HT1A beta receptors) are directly associated with those found in the 5HT levels, varying significantly in relation to the OTC treatments and post-treatment time. These data offer valuable and practical insights for salmonid aquaculture, including the optimization of treatment duration based on given dosages and comprehending the side effects of antibiotic treatments on farmed fish.