Effects of thymol:carvacrol association on health and zootechnical performance of tambaqui Colossoma macropomum

Research in aquaculture shows that isomers thymol and carvacrol are extremely promising additives in fish diet, being classified as potent immunostimulant, antioxidant, and growth promoters. In this study, the effects of the thymol:carvacrol combination (1:1 ratio) on health parameters and zootechnical performance of tambaqui (Colossoma macropomum) were evaluated. The compounds were incorporated in concentrations of 0, 500, 1000, 1500, and 2000 mg/kg of feed. At intervals of 30 and 60 days, fish were sampled to evaluate haematological, biochemical, and immunological parameters, and after 60 days, zootechnical performance, parasitic load, and resistance to bacteriosis were evaluated. After 30 days, the fish that received the highest concentrations of thymol:carvacrol showed a reduction in the number of thrombocytes, a decrease in the number of lymphocytes, and an increase in eosinophils (p â"°¤ 0.05). After 60 days of feeding, haematological parameters were similar between all groups. Regarding the antiparasitic effect of the compounds, all groups that received supplemented diets had a high parasitic load (monogenean infestation) that did not differ from the control group. Regarding the prevention of bacteriosis, high mortality was detected in all groups after experimental challenge with Aeromonas jandaei, with no greater protection for fish fed with thymol:carvacrol. In conclusion, it was observed that the haematological results are different from those described in the literature of aquatic animals and corroborate with research of mammals. Therefore, the anti-inflammatory/immunosuppressive action of thymol and carvacrol are highlighted, which is relevant from a pharmaceutical and medicinal point of view. However, the use of these additives for aquaculture deserves to be discussed carefully, as the cost-benefit of this supplementation for the fish farmer is not a consensus.