Determination of oxytetracycline effects on sea bass (Dicentrarchus labrax, L. 1758) immune system

In this study, sea bass (Dicentrarchus labrax, L., 1758) were fed with oxytetracycline (OTC) supplemented antibiotic bait and it was aimed to determine the effects of antibiotics on the immune system.For this purpose, first group was fed with pellet food that do not include OTC, with 75 mg/kg OTC and 100 mg/kg OTC over 21 days. Blood and tissue samples (kidney, spleen and liver) were taken from fish on the 4th, 7th, 10th, 14th and 21st day to find out the effects of antibiotic and serological, hematological, histopathological and gene expression analyses were performed. The amount of antibiotic distribution in muscle and liver was also examined. The results of hematological and serological analyses showed that number of NBT(+) cells, total leucocyte count, serum lysozyme activity, serum Ig-M and serum C3 levels decreased in the OTC treated groups. Hematocrit level, serum total protein and myeloperoxidase activity results were not significantly varied in the OTC treated groups. Real time quantitative polymerase chain reaction method was used to determine expression levels of Lys-g, Ig-M, IL-1β, C3 and MHC-IIα genes related to immune system. As a result of OTC treatment, expression levels of immune related genes were found to be suppressed on some days of sampling. Antibiotics were also detected to present in muscle and liver tissues. Liver, kidney and spleen tissues were sampled for the histological examination on the 10th and 21st day and the results showed that antibiotic treatment did not have a negative pathological effect.As a result, OTC application in sea bass suppressed the fish immune system. This negative effect depends on the OTC application time (>10 days) and using overdose.