Special Toxicity Effect Of Studies On “miefeiling” In Nile Tilapia(oreochromis Niloticus)

Nile tilapia(Oreochromis niloticus) are members of the Family Cichlidae in Perciformes,native to the eastward flowing rivers of central and southern Africa. Nile tilapia are tolerant of wide fluctuations in salinity, dissolved oxygen, and temperature, with their high fecundity, rapid growth rates and strong adaptability to environment, those characteristics make the Nile tilapia be the most popular of the fishes used in aquaculture by many country and regions. Due to escaping and poor management in aquaculture, whose members have successfully invaded ecosystems worldwide, threatening the survival of native fish and the structure and function of the water ecosystem. our country is the largest country in the tilapia aquaculture production, as the invasion of tilapia a wide range of countries, Nile tilapia has become a model foreign aquatic invasive species, which are widely distributed and bringing prominent damages in the most of the natural waters in the south of China, prevention and control measures are in urgent need. In order to control the population of the Nile tilapia in wild conditions, an organophosphate drug called "Miefeiling" was screened out for the specific toxicity on Nile tilapia by our laboratory. In this study, the acute toxicity test of "Miefeiling" was used to validate the special toxicity,and on this basis, exploring the external and internal pathogenesis of this drug through the tissue slice observation and physiological and biochemical index detection, in order to provides some basic data and theoretical to promote "Miefeiling" to be used. The main results were as follows:1 Toxic effect of “Miefeiling” on the alien Nile tilapiaIn this study, the effect of “Miefeiling” on Nile tilapia and other common fish was verified through the acute toxicity test. Meanwhile, the median lethal concentrations of“Miefeiling” to the Nile tilapia(wet weight, 2.5±0.4 g) at 24, 48, 72 and 96 h weredetermined by the method of semi-static test, and the safe concentration in the environment was also estimated. The result showed that “Miefeiling” had significant toxic effects on the Nile tilapia(P<0.01). The Nile tilapia exposed to “Miefeiling” 0.10, 0.17, 0.20 mg/L for 96 h all died, while the other species including the grass carp(Cteno Pharyngodon idellus),mud carp(Carrhina molitorella), crucian carp(Carassius auratus), loach(Misgurnus anguillicaudatus), zebrafish(Danio rerio), and the White Cloud Mountain minnow(Tanichthys albonubes) swam normally with no symptoms of toxicity. The 24 h, 48 h, 72 h,96 h LC50 values of Nile tilapia were 0.167, 0.077, 0.057, 0.043 mg/L respectively and the safe concentration was 0.0043 mg/L. These results suggested that “Miefeiling” could be used to specifically control the wild Nile tilapia population in small water bodies.2 Histopathology changes in gill, liver and kidney tissues of Nile tilapia exposured to“Miefeiling”Acute toxic effect of “mie feiling” on Nile tilapia(body weight: 34.65 ± 5.69 g) and the histopathology changes in gill, liver and kidney tissues were studied to explain the mechanism specificity poison effect. The 24, 48, 72, 96 h-LC50 of “Miefeiling” on Nile tilapia were 0.148. 0.103, 0.048 and 0.032 mg/L, respectively. Necrosis, desquamation,fusion, shortening and curling of secondary lamellae, secretion of mucous cells were observed in gill tissues after exposed to “Miefeiling”. Hepatic lesions in the fish exposed to“Miefeiling” were characterized by hypertrophy of hepatocytes, vacuolar degeneration,nuclear pycnosis, congestion and cloudy degeneration of hepatocyte. Tubular degenerations, congestion were observed in the kidney tissues of fish after exposure. The damage degree of gill, liver, kidney to the “Miefeiling” increased in order. Therefore the main cause of death in the Nile tilapia was likely to be harm on tissue mentioned above by“Miefeiling”. This study has provided the basic theoretical foundation to reveal the specific mechanism of “Miefeiling” effect on Nile tilapia.3 Effects of “Miefeiling” on acetyl cholinesterase and antioxidant enzyme activity in Nile tilapiaIn order to explore the toxicity mechanisms of “Miefeiling”, an effective drug for theNile tilapia population control, the activity change of acetylcholinesterase(ACh E) and antioxidant enzyme in Nile tilapia were detected after it exposing to “Miefeiling” with the sublethal concentrations. The result showed that: 1) the activity of ACh E in the brain, gill,liver, and muscle tissues were significant inhibited after exposure to “Miefeiling”(P <0.01). 2) when the exposure time increased, the activity of superoxide dismutase(SOD)had no significant change in brain and gill, but significant increased in liver and muscle;the content of glutathione reductase(GSH) decreased significantly in brain but increased in the liver, which increased in gills and muscle firstly and then decreased. The activities of lactate dehydrogenase(LDH) in the four tissues were significantly increased(P < 0.01)and highest in liver. The activity of glutathione s-transferase(GST) firstly decreased and then rose significantly in liver. Results indicated, the oxidative stress reaction had taken place in different tissues in Nile tilapia. The toxic effects of “Miefeiling” may be due to the inhibition of ACh E activity and the promotion of oxidative stress reaction in Nile tilapia.This study had researched the specificity of toxicity mechanism of “Miefeiling” from the Angle of molecular biology enzyme,also had provided the basic data, and a foundation for the subsequent experiment.4 Different effects of exposure to “Miefeiling” on the acetylcholinesterase activity in the tissues of Nile tilapia and Mud carp(Cirrhinus molitorella)In order to explore the special mechanism of “Miefeiling” on the Nile tilapia, we choose Nile tilapia and Mud carp as the subject to detect the living conditions and the changes of ACh E activity at different exposure concentrations and time. The results showed that, in the experiment process of acute toxicity test and recovery in water, the mortality of Nile tilapia and Mud carp exposed to 0.05 and 0.1 mg/L solution were 100% and 0 respectively,the activity of ACh E in the brain of Nile tilapia and Mud carp were decreased significantly with the increasing of concentration and exposure time(P < 0.01); the drop rate of the activity of ACh E in Nile tilapia was much greater than mud carp, and it was irreparability,while the activity of ACh E in the brain of mud carp renewed 96.25% and 79.33% after ten days recovery in clean water. It could be concluded that the “Miefeiling” has high toxicity on Nile tilapia and no obvious toxicity on Mud carp at the low concentration; its selectivepoison mechanism might be related with the different sensitivities to “Miefeiling” on the activity of ACh E between two species. This study explained the specificity of toxicity mechanism of “Miefeiling”, and provided the theoretical basis and data support to put“Miefeiling” used in reality.