| Misgurnus anguillicaudatus is one of the fresh water fishes which are in rising market demands at home and abroad in recent years. Because of its good adaptability,high survival rate and ability of anti-disease, loach has become an important aquaculture object. With the promotion of intensive farming mode, ammonia nitrogen pollution has become a kind of breeding loach process that is one of very common constraint factors in the breeding process. In this study loach were keeping in an ammonia nitrogen stress test, in order to understand ammonia nitrogen pollution of loach toxicology mechanism, and also, an experiment to campare the ammonia nitrogen intimidation ability of the mass selection F2 group and control group of juvenile fish has been done.The results show that :1. A study of loach on ammonia nitrogen stress1.1 Acute toxicological testing of ammonia nitrogen to the loach.With loach as the research object, we construct different ammonia nitrogen concentration environment and breeding time between-group differences of ammonia nitrogen pollution, studies the influence of keeping loach mortality. The results show that:under the pH8.2, temperature 29±1℃, dissolved oxygen 6.5 + 0.5 mg·L-1, the higher the concentration of ammonia nitrogen in water of loach, the higher the loach motality. Its mortality rate of half the total death in 96 houres is 164.4 mg.L-1of ammonia concentration (TAN) concentration and 2.22 mg.L-1 of nonionic ammonia (NH3-N) concentration .1.2 Effects of ammonia-N stress on SOD and GSH-Px activities of three tissues in loachAn ecotoxicological feasibility study was conducted to investigate the effects of ammonia-N(NH4Cl)(0 mg·L-1, 50 mg·L-1, 150 mg·L-1, 250 mg·L-1, 450 mg·L-1 )stress on the activities of SOD and GSH-Px in gill, livers and muscle of Misgurnus anguillicaudatus to ammonia-N exposure in fresh water for 21 days. The results showed: the SOD and GSH-Px activity in gill and liver of Misgurnus anguillicaudatus in the 50 mg·L-1 and 150 mg·L-1groups increased while ammonia–N concentration increasing at 2d and 7d and decreased while the ammonia–N concentration increased at14d and 21d(P<0.05);the SOD and GSH-Px activity in the 250 mg?L-1 and 450 mg?L-1 groups decreased consistently during experimental period. The acvtivity of SOD and GSH-Px in muscle of Misgurnus anguillicaudatus to ammonia-N is not as sensitive as that in livers and muscle,the activity of SOD in the low concentrations is induced at 14d,and be inhibited in the highest concentration;while the trend of the activity of GSH-Px is opposite to SOD activity in muscule.Ammonia-N stress significantly affected the physiological -biochemical parameter of Misgurnus anguillicaudatus, with ammonia–N concentration increasing and time prolonged, ammonia-N inhibited antioxidant enzyme obviously.1.3 The effects of ammonia-N stress on the structures of gills and liverAn ecotoxicological feasibility study was conducted to investigate the effects of ammonia-N(NH4Cl)(0 mg·L-1,50 mg·L-1,150 mg·L-1,250 mg·L-1,450 mg·L -1)stress on the structures of gills and liver. After 21d exposed in different anmmonia-N concentration, the gills and liver samples were taken to applicate scanning microscope and transmission electron microscope. Results showed that: compared with the control, with the ammonia-N concentration increased, loach gills in 21d appeared different tissue injury:in low concentration, the gills of loach appeared a large number of filaments on the surface, the cells edema and uplift secretion; in the middle concentration group,an increased secretion on surface of gill filaments, desquamation and hypertrophy of epithelia cells, evident damage of filaments tips. High concentrations of group gills necrosis and the epithelial tissue structure disappeared. The ultrastructure of loach liver cell under ammonia nitrogen in different concentrations appeared different degree of damage: In the two low concentrations mitochondria of liver cells was diformed, endoplasmic reticulum had expension, and nuclear membrane swelling; in 250 mg·L - 1 concentration group liver cell structure was damaged and cell cytoplasm content large leakage and cytoplasm vacuoles, the structure of the remaining organelles are incomplete; 450 mg.L-1 concentration appeared a massive cell apoptosis. With ammonia-N concentration increased, the damage in gill tissue and liver cells gradually seemed deeply, and the damage was irreversible. 2. Ammonia-N to juvenile loach of F2 generation breeding group and of control group on acute toxicity and genetic toxicity。Study on ammonia-N to juvenile loach of F2 generation breeding group and of not breeding group on acute toxicity and genetic toxicity in conventional biological toxicity testing method.The results show that:under the pH8.0, temperature 25.0±0.1°C, the higher the concentration of ammonia nitrogen in water of loach, the higher the death rate. Loach of selection breeding group mortality rate of half the total death in 24,48,72,96 houres are 681.29 mg·L-1, 239.50 mg·L-1, 179.57 mg·L-1, 148.74 mg·L-1of ammonia concentration (TAN) concentration and the control group is 599.48 mg·L-1, 240.18 mg·L-1, 166.09 mg·L-1, 108.57 mg·L-1. Micronuclear test was used to examine the genotoxicity of ammonia-N on juvenile loach of F2 generation breeding group and of control group. The results showed that:both micronucleus and nuclear abnormity rate were significantly changed with the increasing concentration of ammonia-N. With the increasing of the concentration of ammonia-N,both the loach micronucleus and nuclear abnormity rate were at first increasing then decreesing; Breeding group in red blood cells micronucleus and nuclear abnormity rate were always lower than the control,and showed stronger resistance to ammonia stress.3. Growth performance of mass selection F2 generationBased in taihu lake loach population, we adopted the mass selection method as an artificial breeding method, produced the F2 generation and used it for breeding growth performance analysis test, the results showed: Compared with the control group, the daily growth rate of F2 was improved 4.7%, while variation coefficient of body weight and length was reduced by 9.8% and 8.1%, respectively. All these showed that after one generation artificially breeding operation in the morphological characteristics, loach tend to be more consistent, and its growth performance also made a further improved. |
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