Acute mercury exposure affects the redox status system, fatty acid profile and the ovarian morphology of the solitary ascidian Ciona intestinalis (Chordata, Tunicata).

Mercury is one of the most harmful pollutants in aquatic ecosystems. The present study assessed the effects of gradual concentrations of mercury (1, 10, 50, and 100 μg L-1) on the antioxidant status and fatty acid profiles in the viscera of the solitary ascidian Ciona intestinalis (Linnaeus, 1767). Additionally, histological analyses were conducted on the ovary to evaluate morphological changes induced by mercury exposure. The results revealed an increase in malondialdehyde (MDA), protein carbonyl (PCO), glutathione (GSH) and glutathione S-transferase (GST) levels. Additionally, metallothionein (MT) levels increased, while acetylcholinesterase (AChE) activity decreased. Mercury exposure also altered the fatty acid profile, particularly monounsaturated fatty acids (MUFAs) and polyunsaturated fatty acids (PUFAs) especially within the omega-3 and omega-6 families. Biochemical parameters were confirmed by the histopathological analysis, indicating significant morphological alterations in the ovaries of C. intestinalis, Irregular nuclear membranes, loosening of the cytoplasm and detachment of test and follicular cells from the oocyte membrane were observed.The complete destruction of the oocytes was noted at the highest mercury exposed ascidians.