Effect of Thymol oil on the growth performance and survival of African catfish (Clarias gariepinus) challenged with Aeromonas hydrophilia

Abstract

Intensive aquaculture systems are associated with outbreak of diseases that cause economic losses. Over the years, diseases have been managed with antibiotics that are presently linked to environmental contamination and deposition of residual antibiotics in fish and people that consume such fish. Therefore, Thymol oil, a harmless product with antibacterial properties was used in the production of African catfish, to determine the effects on the growth performance, immune response and survival of the fish challenged with infestation of Aeromonas hydrophilia. A 40% protein basal diet was formulated, and Thymol oil (TMO) was added to it at (0, 0.8, 1.1, 1.4 and 1.7%) respectively making diets/treatments 1 to 5. The diets were fed in triplicate to African catfish juveniles to apparent satiation, twice daily for 70 days. Results showed that dietary Thymol oil significantly improved the fish growth performance in relation to fish fed diet without the oilcontrol diet). For instance, the mean weight gain increased consistently from 9.62 g in fish fed the control diet to 22.8g in fish fed diet with 1.70% thymol oil. Contrarily, the dietary thymol oil significantly 
reduced white blood cells and the carcass cholesterol. The WBC decreased from 8.70 103 mm3 in fish fed the control diet to 4.80 103 mm3 in fish fed diet with 1.70 % thymol oil. Also, the cholesterol decreased consistently from 85 mg/dl in fish fed the control diet to 65 mg/dl in the fish fed diet with 1.70% thymol oil. The biochemical profile of the fish revealed that dietary thymol oil significantly increased the glutathione peroxidase, serum albumin, globulin and serum protein with increasing levels of the oil in the diets. Also, dietary thymol oil improved the survival rate of the fish when 
challenged with the infestation of Aeromonas hydrophilia. In conclusion, dietary thymol oil improved the growth performance, immunity and survival of African catfish. However, more research is needed to determine the optimum level of the thymol oil for the best growth performance of the fish.