studying protective effects of thymol on the growth factors of juvenile common carp following chronic mercury (ii) chloride exposure

Background: heavy metals are non-degradable pollutants, and mercury is one of them. it can harm fish and reduce its growth rate. one of the most effective ways to reduce the side effects of heavy metals is to use herbal compounds or their active ingredients. thymol is a natural monoterpene in plants’ essential oils, such as thyme. the positive effects of this substance have been proven to improve growth indicators in some fish, such as grass carp.objectives: this research was conducted to investigate the protective effects of thymol on the growth factors of juvenile carp exposed to mercury.methods: in the present study, 120 common carp (cyprinus carpio) were randomly divided into 4 groups (control, hgcl2, thymol, and thymol+hgcl2). each group was replicated three times and included 10 fish. at first, the initial weight of the fish (w0) was recorded, and then the fish were kept for 56 days. the control group fish were fed basic food and kept in mercury (ii) chloride-free water. during 56 days, the fish of the thymol and thymol+hgcl2 groups were fed with food containing thymol 100 mg/kg feed. the tank water of the fish of the thymol+hgcl2 and hgcl2 groups contained 0.44 mg/l mercury chloride. after 56 days, the final weight (wt) of the fish was also measured, and the growth factors (absolute growth, absolute growth rate, specific growth rate [sgr], food conversion ratio [fcr], and food conversion efficiency [fce]) were calculated.results: this research showed that thymol has a protective effect on growth factors following chronic mercury exposure. thymol in the thymol+hgcl2 group significantly improved absolute growth, absolute growth rate, and fcr compared to the hgcl2 group. also, thymol significantly improved sgr and fce factors, although there was no significant difference with the mercury group.conclusion: thymol can effectively reduce the side effects caused by mercury chloride exposure in common carp.