| In the seedling production of Litopenaeus vannamei,the ammonia nitrogen concentration in the whole culture cycle often exceeds the safe range due to the large stocking density and easy decomposition of baits,although there is a large amount of water exchange,which causes damage to the growth and development of larvae.At the same time,the instability of water quality makes the larvae often in a susceptible state,the immunity to Vibrio decreases,and the excessive Vibrio in the larvae causes the poor quality of the seedlings.Algae-bacteria biofloc system have attracted much attention because of their advantages such as systematic closure,controllable,stable water quality,improved immunity of prawns and improved utilization of baits.At present,there are few reports on the application effect of algae-bacteria biofloc system in the seedling production.From the following three parts,this paper explores the main regulatory factors of algae-bacteria biofloc system applied in the seedling production of Litopenaeus vannamei.1.Effects of light intensity on the breeding of Litopenaeus vannamei under algalbacterial-based biofloc systemIn order to explore the effects of light intensity on the breeding of litopenaeus vannamei under algal-bacterial biofloc technology system,three different lights systems was designed for experiment,including light of 200 W(L200),light of 100 W(L100)and light of 0 W(L0).The light intensity of three groups is(8422 ± 195)lx?(4400 ± 204)lx and(3 ± 1)lx.During the experimental Period,larvae was cultured for 14 days in a zero-water exchange system.The results showed that the algal-bacterialbased biofloc system can control the water quality well,and increase the light intensity can effectively reduce the drop of p H and alkalinity.The body length and weight of larva in L200 were significantly higher than those in other groups(P < 0.05).High intensity light improved the survival rate of larvae and reduced the proportion of total vibrio in water,but there was no significant difference among each group(P > 0.05).Additionally,the moisture content of larva in L200 was significantly lower than that in other groups(P < 0.05).The effect of light intensity on crude Protein and crude fat content was not obvious.Significantly,there was no difference in the nutritional composition of BFT in each group(P > 0.05).The results demonstrated that the application of a certain amount of light intensity in the algae-bacteria system was beneficial to control water quality and enhancement of shrimp quality.2.Effects of different concentrations of algal-bacterial-based biofloc on the breeding of Litopenaeus vannameiTo explore the effect of TSS concentration on the larval culture of litopenaeus vannamei in the algae-bacteria biofloc system.Control group without BFT,group T300 with BFT to regulate TSS to 300 mg/L and group T600 with BFT to regulate TSS to about 600 mg/L were set up in the experiment.The actual initial TSS concentrations of the three groups after flocculation were measured as follows:(212 ± 12)mg/L,(285 ± 9.2)mg/L and(616 ± 6.9)mg/L,respectively.In the control group,water quality was controlled by water exchange,while in the group T300 and group T600,water was not exchanged,and the experiment lasted for 14 days.The results showed that the average concentration of ammonia nitrogen in the control group was significantly greater than that in the other two groups and exceeded the safety level.The average level of nitrous nitrogen in the three groups was within the safe range.The concentration of nitrate nitrogen,total nitrogen and TSS increased with the increase of TSS concentration,while the alkalinity and p H decreased with the increase of TSS concentration.There was no significant difference in the total number of Vibrio in water between groups.There was no significant difference in body length among the three groups.The dry weight,survival rate and survival rate under salinity stress of the shrimp in the group T300 were significantly higher than those in the group T600,and there was no significant difference in the total number of vibrio in the shrimp.In conclusion,compared with the traditional aquaculture mode,the algae-bacteria biofloc system has obvious advantages in saving water resources,controlling water quality and enhancing the body weight of larvae,but the TSS concentration should not be too high,300 mg/L is the appropriate initial concentration.3.Effects of different stocking density on the breeding of Litopenaeus vannamei under algal-bacterial-based biofloc systemThe stocking density is also an important factor causing the stress of prawns.Too low density cannot effectively utilize the productivity of water body.Too high density will cause fluctuation of water quality and reduce the seedling survival rate.Compared with other aquaculture modes,algae-biofloc system is more stable in water quality control.In this experiment,we try to increase the stocking density to explore the Productivity of algae-biofloc system.Three different densities of 200 tails/L(group D200),300 tails/L(group D300)and 400 tails/L(group D400)were set for the experiment.No water change and carbon source were added during the whole cultivation process,and the larvaes were cultured for 14 days.The results showed that the average concentration of ammonia nitrogen,nitrous nitrogen and the total number of vibrio in water increased with the increase of stocking density,but the difference of the average concentration of nitrate nitrogen and total nitrogen was not significant.The concentration and alkalinity of chlorophyll-a in D400 were significantly lower than those in other two groups.Increasing the density of stocking feeding leads to an increase in the amount of bait feeding,which decreases the stability of water quality.The body length,body weight,survival rate and survival rate under salinity stress in the D200 were significantly higher than those in the other groups.Although the survival rate of young shrimp decreased with the increase of stocking density,the increase of stocking density would lead to the decrease of shrimp stocking quality.In summary,200 tails/L in seedling Production is the appropriate stocking density for the algae-bacteria biofloc system. |
PDF Full Text Request