Abstract: To clarify the toxic effects of low-molecular-weight polycyclic aromatic hydrocarbons on aquatic organisms, we examined the effects of phenanthrene (Phe) on the liver structure and related enzyme activities of female and male loach (Misgurnus anguillicaudatus). Loaches were exposed to different concentrations of Phe aqueous solution (1.29, 1.67, 2.16, and 2.79 mg·L^-1, respectively) in hydrostatic water. Loaches that were kept in an acetone solvent were used as control, while those in deionized water were used as the blank control group. Loach samples were harvested on day 7, 14, 21, and 28 after the treatments respectively. Rie’s colorimetric method was employed to determine the changes of aspartate aminotransferase (AST) and alanine aminotransferase (ALT) activities in the liver of loach. The liver tissue slices of loaches under Phe stress for 14 and 28 days were prepared, stained with hematoxylin-eosin (HE) and observed. The results showed that compared with the control groups, the activities of AST and ALT exhibited a trend of significant increase and then decrease with the increases of Phe stress concentrations and treatment duration, showing a certain dose effect and time accumulation effect. In addition, the activities of AST and ALT of female loaches were significantly higher than those of males. Liver histological results showed that when loaches were treated by 1.29 mg·L^-1 Phe for 14 days, their hepatocytes were slightly swelled, and a few hepatocytes appeared nuclear lysis, deformation and vacuolization. When loaches were treated by 2.79 mg·L^-1 Phe for 28 days, their liver tissue was severely damaged, and the liver structure of the male was more severely damaged. Our results indicated that Phe can induce firstly and then inhibit AST and ALT in the liver of loach, and such effect is stronger in female loaches. Continuous stress of high-concentration Phe can cause significant damage to liver tissue, and the magnitude is more significant in male than female loaches.

Key words: phenanthrene, Misgunuis anguillicaudatus, liver, transaminase, histological structure.