| Currently,the survival rate of Litopenaeus vannamei showed a declining trend.In addition to the degradation of germplasm may be the main reason,breeding technology is one of the important factors which cannot be ignored.To understand the impact of different ecological factors on the growth of L.vannamei larvae is important to guide the actual seedling production.In this study,the effects of different light,temperature and density on the growth,resistance and antioxidant enzyme activities on L.vannamei larvae were investigated,and the optimal conditions of them for larviculture were explored.The results of this paper are as follows:1.The experimental setup of light color including five groups: red light,yellow light,blue light,green light and dark control.Contrast with the dark group,red light,yellow light,blue light,green light have a great impact on metamorphosis of L.vannamei larval.Under blue light,the total time of Z? to P1 is the longest(262.83 h),which is 28 h more than the control group.Under yellow and red light,when larval development to P1,the survival rate were low,with 14.49% and 18.46% respectively.L.vannamei larvae at different developmental stages have different sensitivities to different colors light.Red and yellow lights have a more significant impact only on zoea,and blue and green lights have an impact on the entire developmental stage.Take metal halide lamp as light source,there was significant difference(P<0.05)observed among the four light intensity gradients(0,1500,5500 and 12000Lux)on larval survival and metamorphosis.In the experiment,Larvae of the 12000 Lux group experienced the longest time(257.33 h)from Z? to P1,and had the lowest survival rate of 1.63%.In zoea period,when the light is greater than 1500 Lux,metamorphosis time of larval increased and the survival rate of 12000 Lux group was significantly lower than that of other groups(P<0.05);In mysis,the light group developed faster than the dark group and the difference was significant(P<0.05),after that,the difference of each group gradually decreased and the survival rate decreased significantly than the dark group;when the shrimp stage,there were no significant differences in the development time(P>0.05)in the groups.2.Water temperature has a significant effect on the metamorphosis and survival of L.vannamei larvae.In the experimental groups of 27 ?,30?,33 ?,36 ?,the higher the temperature,the shorter the metamorphosis time of larvae,but the lower the survival rate.The total metamorphosis time of larval from Z? to P1,36? group is the shortest for 232.17 h,and 27? group is the longest for 260.17 h.33? group is 241.83 h,and 30? group is 252.33 h.When larvae development to P1,the survival of 27? group was the highest for 63.01%,36? was the lowest,only 13.26%.33? group was 44.25%,30? group was 47.53%.Shrimp seedlings cultivated from different temperatures have a differences in their resistance and late growth.Larvae cultivated at Low temperature have strong ability of anti-Concha,to concha 60 minutes and take them back in the water,the survival rate of 27? group was 73.33%,36?group was the lowest to 48.28%.However,in ammonia and nitrite tolerance test,the higher the temperature,the stronger the tolerance,the endurance of shrimp of 27? group is the weakest,significant difference(P<0.05).After cultured 40 days,the average body weight and body length of shrimp from 33? group is the highest,for 3.691g/tail and 7.382cm/tail.The average body weight and body length of 27 ? group is minimum,for 3.07g/tail and 6.342cm/tail,significant difference(P<0.05).3.Larvae were divided into 4 density experiment groups: D1: 10 × 104/ m3,D2: 20 × 104/ m3,D3: 30 × 104/ m3 and D4: 40 × 104/ m3.There was no significant difference between the Zoea period of each development time(P>0.05),the higher the density of larvae,the longer the development time,the difference was significant(P<0.05),and the total time of D1,D2,D3 and D4 groups developed to P1 are 215.68 h,222.67 h,238.51 h and 247.17 h respectively.Larvae from high-density cultivation are more prone to death,especially at early zoea and late mysis,there was no significant difference in survival(P>0.05)in other periods.The shrimp cultivated in low-density have a good ability of anti-Concha.The ability of resist salinity mutations of shrimp can be improved to increase the density at some degree.Among four groups,D3 group is the best,but D4 group decreased significantly.At low concentrations of ammonia,tolerance of D1 group is better(P<0.05),in the seawater of high ammonia nitrogen concentrations,the tolerance ability of the groups was no significant difference(P>0.05).The shrimp farmed 40 days under good environments,the average weight and average body length of shrimp from D4 group are the lowest,with 2.811 g /tail and 6.438 cm/tail,was found significant differences compared to D1,D2 groups(P<0.05).The average weight and average body length of shrimp of D1 group are the highest,for 3.603 g /tail and 7.065 cm /tail.The average weight and average length between D3 group and D2 group have little difference(P> 0.05).4.Temperature can affect the activity of antioxidant enzymes of L.vannamei larvae.As the larvae grow,catalase(CAT)activity increased gradually,and 36? group had a greater rise.From zoea to mysis stage,the glutathione peroxidase(GSH-PX)activity and total superoxide dismutase(T-SOD)activity of larvae of 33? and 36? group was significantly decreased(P<0.5),and there is little difference between 27? and 30? groups(P>0.05).The malondialdehyde(MDA)content was the highest of each group at P2 stage.And among them,the highest was 36? group,followed by 27? group,indicated that both the low and high temperatures can cause oxidative damage.5.Stocking density can affect the activity of antioxidant enzymes of L.vannamei larvae.The catalase(CAT)activity could gradually rise as the larvae grow,but the difference among different densities on CAT activity is not obvious.From zoea to mysis stage,the glutathione peroxidase(GSH-PX)activity of D3,D4 groups decreased,there was no significant difference between the groups D1 and D2(P>0.05).The superoxide dismutase(T-SOD)activity of each group was similar.The stocking density has little effect on the T-SOD activity of larvae.The malondialdehyde(MDA)content is the highest for each group at mysis stage,the MDA content of D3,D4 group larvae were significantly higher than D1 and D2 groups(P<0.05),and suffered more oxidative damage than the later two groups,especially the D4 group. |
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