Stress And Biological Response Of Naphthalene On The Antioxidant Defense System In Zebrafish (Danio Rerio)

Naphthalene is an important chemical raw materials, which is widely used in the industry. It can access to water through urban sewage, industrial waste, atmospheric deposition, surface runoff and leaching of soil and so on, which endangers the growth, the development and the reproduction of aquatic creature's life and has potential damage on the human health. Now it has become a new topic in the water quality protection.In this paper, we studied the effects of naphthalene on the antioxidant defense system in the visceral mass and the muscle of zebrafish. First, the median lethal concentration(LC50) of naphthalene to the zebrafish for 24, 48, 72 and 96h were obtained using the acute toxicity test, which were 11.9, 11.9, 11.8 and 11.8 mg·L-1 respectively, then based on 96h LC50, we setted up five treatments(0, 1/6 LC50, 1/4 LC50, 1/3 LC50 and 1/2 LC50) and exposed zebrafish to these treatments for 0.5, 1, 2, 4, 7 and 14d respectively. Visceral masses and muscles of zebrafish were collected to determine the activities of superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx), glutathione S-transferase (GST) and the content of glutathione (GSH).We get the following conclusions:(1) In the visceral mass of zebrafish, SOD activities were increased and then restrained after 2d, CAT activities were inhibited almost in the all treatments after 1d. While the activities of GPx, GST and the contents of GSH responded at 0.5d, GPx activities in the low-concentration treatments(1/6 LC50 and 1/4 LC50 treatments) were activitied on the whole test, but were inhibited in high-concentration treatments(1/3 LC50,1/2 LC50 treatments) only at 14d, GST activities and GSH contents in the all treatments were almost lower than that of the control. However, the changes of antioxidant defense system in the muscle of zebrafish were different from those in the visceral mass. SOD activities responded almost at 14d, CAT activities were restrained and then increased after 1d. While the activities of GPx, GST and the content of GSH also responded at 0.5d, GPx activities were restrained and then increased on the whole, the activities of GST were activitied and the contents of GSH increased fistly and then recured to the control level. According to the response time and trend of SOD, CAT, GPx, GST and GSH in various treatments, we concluded that GPx, GST and GSH were more sensitive than SOD and CAT both in the visceral mass and in the muscle of zebrafish.(2) On the 14th day of the test, except for CAT and GPx activities in the low concentration, other antioxidants activities were all inhibited in the visceral mass of zebrafish, which might show that the accumulation of reactive oxygen didn't have an impact on the visceral mass in the low-concentration treatments, but caused the damage of the visceral mass in the high-concentration treatments and inhibited the activities of antioxidants. However in the muscle of zebrafish, CAT and GST activities were activitied, SOD activities appeared increase in the low-concentration treatments and slight inhibition in the high, the contents of GSH and the activities of GPx returned to the basic level of control, which indicated that the muscle of zebrafish exposed to naphthalene might not be resulted in the serious oxidative damage and was still in the range that the body can adjust.(3) Compared with the trend of antioxidants in the visceral mass and in the muscle, we concluded that antioxidants in the visceral mass were more sensitive than in the muscle. Thus, the effects of naphthalene on GPx, GST and GSH in the visceral mass of zebrafish might be used as biomarkers to estimate the biological effect of fish exposed to polycyclic aromatic hydrocarbons.