| The toxicity of ambient ammonia-nitrite on juvenile Mylopharyngodon piceus was studied and the toxicity mechanism of ammonia-nitrtie by juvenile Mylopharyngodon piceus was elucidated. Besides, the effects of dietary vitamin C and E supplementation on the ability of anti-stress was discussed. The results could provide more basic information for aquatic animal toxicology, nutritional immunology, and references for establishing the system of stress evaluation and adjusting anti-stress ability, which could boost the sustainable development of aquaculture.1. In this experiment, the toxic of ammonia-N on juvenile black carp which initial weight was7.9±0.4g was studied, and the water temperature was26±1℃, pH was7.4±0.1, dissolved oxygen content was over6.0mg/L. The results showed that the toxicity were significant positive correlation between the ammonia-nitrtie and maintained time. The24、48、72and96h median lethal concentration of total ammonia-nitrtie were80.98、59.56、44.33and36.40mg/L, respectively, and the safe concentration was3.759mg/L. The24、48、72and96h median lethal concentration of molecular ammonia were1.21%0.89%0.66and0.54mg/L, and the safe concentration was0.054mg/L2. The object of this study was to evaluate the effects of ammonia on the gill NKA, microstructure and serum biochemical indices of juvenile black carp, Mylopharyngodon piceus. The black carp, which initial average weight was7.00±0.14g, were transfer off the freshwater and exposed to different ammonia levels:0mg/L (low, control),10mg/L (middle) and20mg/L (high) NH4C1and sampled randomly at0,6,12,24,48and96h. The results indicated that the gill NKA in the middle and high ammonia group were decreased the minimum at12h,6h, respectively, all reached the maximum at48h, and decreased to the same level as control after96h. Gill microstructure observation, chloride cell in middle ammonia group increased at12h; pavement cells fall off partly at24h; chloride cells vacuolation partly, blood capillary fractured and red blood cell overflowed at96h. But in high ammonia group, chloride cell increased at6h; pavement cells fall off partly at12h and largely at24h; After96h, blood capillary fractured on the base region of the lamellae and congestion, pillar cell disorganized of arrangement. Cortisol and GLU changed in serum were increased the maximum at12h ammonia-nitrtie exposed time, and positive correlation with ammonia-nitrtie, then recovered to the same level as control after 48h. T-SOD has the maximum at6h (P<0.05) and the middle group recovered in the control level at12h, but the high group significant lower than the control group at96h (P<0.05). CAT showed decrease and increase tends respectively during12h, then recovered to the control level after48h. T-AOC and GSH showed decrease tends, MDA and ALT showed increase tends at first. After96h, GSH and ALT were recovered at the control group level, however, the MDA in ammonia-nitrtie group was significant higher than control group and T-AOC in high ammonia-nitrtie group was significant lower than control group. All the results indicated that the ammonia-nitritie stress could serious disturb the antioxidant system, the MDA increased significantly. The change became smooth afterwards adjusted by itself, however, the antioxidant capacity decreased and gill structure destroyed.3. Studies were conducted to investigate the effects of dietary vitamin VC on growth, immunity and anti ammonia-nitrite stress ability in juvenile black carp, Mylopharyngodon piceus (Initial average weight7.27±0.40g). Six iso-nitrogenous and iso-energetic diets were formulated to supply at dosages of0(control),50,100,200,400and800mg/kg vitamin C diet, respectively. After feeding8weeks, according to specific growth rate, three group of0,200and800mg/kg of black carp were subjected to an ammonia-nitrtie stress (20mg/L) for24h. Results indicated that the optimal vitamin VC content for maximum growth is about252.0mg/kg. The vitamin VC concentration in liver and muscle were positive correlation with VC content in diet, and no significant differences were observed among fish fed the diets with equal to or higher than400mg/kg of vitamin VC. No significant differences in T-SOD and MDA were observed among dietary treatments, but VC could significant increased the CAT and GSH-px activity (P<0.05), With the VC content increased, CAT were increased at first and then decreased. GSH and NKA were increased when VC concentration in diets were increased, Cortisol were decreased at first and then increased. After ammonia-nitrite stressed, each group of the VC concentration in liver, T-SOD, CAT, GSH-px activity and GSH content in serum and gill NKA activity were decreased, cortisol and MDA content were increased. The T-SOD, CAT and NKA activity, GSH, MDA and cortisol content were significant changed at ammonia-nitrite stressed before and after. Liver vitamin C concentration in fishes fed VC diets were significant decreased after stressed, however, there are no significant changed in CAT, NKA activity and GSH, cortisol content compared with control group. T-SOD activity in200mg/kg vitamin C diet was no significant changed at stressed before and after, but GSH-px activity and MDA content were significant changed. In 800mg/kg vitamin C group, GSH-px activity and MDA content were no significant changed except T-SOD activity. All the results indicated that the vitamin C requirement of juvenile black carp for optimal growth might be252.0mg/kg diet. Fish have significant stressed when put in ammonia-nitrite, and VC concentration in diet could improve immunity and anti ammonia-nitrtie stress ability of black carp.4. Studies were conducted to investigate the effects of dietary vitamin E on growth, immunity and anti ammonia nitrite stress ability in juvenile black carp, Mylopharyngodon piceus (Initial average weight7.02±0.13g). Six iso-nitrogenous and iso-energetic diets were formulated to supply at dosages of0(control),25,50,100,200and400mg vitamin E equivalent kg-1diet, respectively. After feeding8weeks, according to growth, three group of0,100and400mg/kg vitamin E group of black carp were subjected to an ammonia-nitrite stress (20mg/L) for24h. Results indicated that the optimal VE content for maximum SGR is about130.0mg/kg. The vitamin E concentration in liver and muscle were positive correlation with vitamin E content in diet, and no significant differences were observed among fish fed the diets with equal to or higher than200mg/kg of vitamin E. No significant differences in gill NKA activity were observed among dietary treatments, but with the vitamin E content in diets increased, T-SOD and CAT activity were increased and MDA content decreased. Each group of muscle vitamin E concentration and CAT activity were not affected by ammonia-nitrite stressed, but liver vitamin E concentration were significant decreased(P<0.05). After stressed, T-SOD and gill NKA activity in control group were significant decreased and cortisol content was significant increased (P<0.05). But two vitamin E supplemental group of T-SOD, NKA activity and cortisol were no significant changed. MDA content in each group were significant increased after stressed, however, the400mg/kg vitamin E group MDA content was significant lower than control group (P<0.05). All the results indicated that the VE requirement of juvenile black carp for optimal growth might be130mg/kg diet, and higher vitamin E supplement in diet could improve non-immune response and anti ammonia-nitirite stress ability of black carp. |
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