Degree/Year : MVSc/2021

4-nonylphenol (4-NP) is a phenolic endocrine disrupting compound and used in various industrial products. It possess health threat to both human and aquatic animals. During the study, 360 adult male zebrafish (Danio rerio) were used to investigate toxicity of 4-NP on brain and eye tissues of zebrafish after daily exposure for 21 days. For experiment, zebrafish divided into four groups viz., control (C1), vehicle (C2), treatment 1 (T1) and treatment 2 (T2), consists of 90 zebrafish in each group. C1 group kept in R.O. water, C2 group kept in water with absolute ethanol as vehicle at 10 μl/L of water, T1 and T2 groups kept in water with 4-NP @ 100 μg/L and 200 μg/L of water, respectively. Anxiety behaviour and locomotor behaviour of zebrafish evaluated on day 8, 15 and 22 of the experiment period using light-dark preference test and novel tank test. During light-dark preference test parameters viz., time spent in light side, time spent in dark side, numbers of entries in dark side and latency to light side were considered. For novel tank test, time spent in upper zone, time spent in lower zone, numbers of entries in upper zone and numbers of entries in lower zone were considered. Exposure of 4-nonylphenol significantly affected behaviour parameters in both T1 and T2 groups as compared to C1 group. There was significant increase in time spent in dark side and time spent in lower zone in T1 and T2 groups as compared to C1 group. However, time spent in light side, time spent in upper zone, number of entries in upper zone and number of entries in lower zone were decreased significantly in T1 and T2 groups as compared to C1 group. Total number of entries in dark side was non-significantly decreased in T2 group on day 8 and 15, whereas significantly decreased on day 22 of experiment as compared to C1 group. In brain and eye tissue, significant decreased activity of SOD and level of GSH found in T1 and T2 groups as compared to C1 group. However, MDA level is significantly increased in T2 group as compared to C1 group. The activity of CAT in T1 and T2 groups is decreased non-significantly in brain and decreased significantly in eye as compared to C1 group. mRNA expression level in zebrafish brain and eye from T2 group showed significant down regulation of SOD, CAT and Nrf2 levels as compared to C1 group. Microscopic changes between control and other groups were comparable.