| Tilapia is the main freshwater aquaculture fish in China.Because it is not resistant to low temperature,it can not naturally winter in most parts of China.In order to quickly raise the market specifications when the temperature is suitable,the economic benefits of tilapia breeding in the next year are guaranteed.A large number of high-quality wintering seedlings must be provided each year.The traditional water-flowing wintering cost is high,the environmental impact is large,and the temperature is not well controlled.The closed farming mode can make up for these shortcomings.The Recirculating Aquaculture System(RAS)and The Bio-floc Technology(BFT)system is a commonly used closed culture mode.In this study,we used the RAS and BFT to carry out the low temperature wintering culture experiment of GIFT Oreochromis niloticus and the cultivation of largesized seedlings,and monitored the water quality index and fish growth index during the breeding process.The structure of the intestinal flora of the two systems of aquaculture water and fish was identified,and the nitrogen and phosphorus budgets and aquaculture costs of the system were analyzed.The effects of wintering and temperature control of the two models of cultured tilapia were evaluated.1.Study on low temperature culture of Tilapia and its nitrogen and phosphorus budget in RAS and BFTIn order to study the effect of low-temperature tilapia cultivation with RAS and BFT system,the growth,water quality,cultivation cost and nitrogen and phosphorus budget of the system during low-temperature tilapia cultivation with GIFT Oreochromis niloticus were compared by using RAS and BFT cultivation system.The experiment was divided into RAS group and BFT group and cultured for 64 d.The results showed that the survival rate of tilapia in RAS group reached 96.9 ± 2.23 % during the cultivation period,which was significantly higher than that in BFT group 65.82 ± 3.22 %.The feed coefficient of BFT group was 1.31 ± 0.03,which was significantly lower than that of RAS group.During overwintering,the TAN in RAS and BFT were 1.56 ± 0.76 and 1.58 ± 0.56 mg/L,respectively,with no significant difference in average concentration.The average concentration of nitrite in RAS group was 0.47 ± 0.29 mg/L,which was significantly higher than that in BFT group,but both were maintained below 1 mg/L.Nitrate continued to accumulate in both groups,and eventually reached 118.4 ± 0.92 mg/L in RAS group and 336.91 ± 21.44 mg/L in BFT group.In terms of total cost,RAS system is higher than BFT system in terms of electricity consumption,water consumption and feeding quantity.In terms of nitrogen and phosphorus budget,the most important nitrogen and phosphorus input in the two groups were feed,which were 94.04 ~ 94.26 %,94.82 ~ 95 % and 77.63 ~ 85.15 %,78 ~ 84.25 %,followed by fish.The fish in the RAS group accounted for 5.39 ~ 5.61% and 4.5 ~ 4.67 % of nitrogen and phosphorus input respectively,and the BFT group accounted for 12.65 ~ 19.37 % and 10.35 ~ 16.1 % respectively.The common output pathway of nitrogen and phosphorus in RAS group and BFT group was harvested fish,which accounted for 32.61 ~ 40.27 % and 23.21 ~ 28.37 % of the total nitrogen and phosphorus input in RAS group respectively,and 43.89 ~ 53.67 % and 30.24 ~ 32.54 % in BFT group respectively.The relative utilization rates of nitrogen and phosphorus in the BFT group were 40.25 ± 4.43 % and 22.92 ± 1.89 %,respectively,slightly higher than those in the RAS group 33.19 ± 4.05 % and 22.92 ± 1.89 %,but the differences were not significant(P > 0.05).RAS group is 59.73 ~ 67.39 % and 71.63 ~ 76.79 % of nitrogen and phosphorus,the BFT group is 46.33 ~ 56.11 % of the nitrogen and 67.46 ~ 69.76 % of phosphorus was lost to the environment,the RAS group to be significantly higher than that of BFT group(P < 0.05),the results show that the object of BFT model can effectively improve the breeding utilization rate of nitrogen and phosphorus,reduce the discharge of wastes breeding,reduce the impact on the ecological environment,the RAS and BFT system can realize the low temperature of tilapia aquaculture and maintain a stable water quality,preliminary cost estimate BFT under the RAS.2.Analysis of the flora structure of water,intestine and gill in two wintering culture patterns of tilapia based on high-throughput sequencing technologyHigh-throughput sequencing technology was used to detect the microorganisms in the water,biological filter and intestinal and gill of the cultured fish in the two overwintering cultivation modes of tilapia,and the composition and distribution of the microflora in each sample were obtained.The effective sequence coverage of all samples exceeded 99 %,and the sequencing results were reliable.The results showed that according to Chao1 index and Simpson index,the microbial richness in water in the RAS group was higher than that in the BFT group,but the diversity was lower than that in the BFT group.The flocculation microbial richness and diversity in the BFT group increased with the increase of breeding time,while in the RAS group it was on the contrary.The intestinal microbial diversity and richness of BFT group were less than RAS group,but the gill richness was less than RAS group,and the diversity was the opposite.In the initial stage of RAS group,Proteobacteria was the dominant Bacterium,and the abundance reached 75 %.The rest were Actinobacteria(9 %),Firmicutes(7 %),Paracoccus(34 %)and Methylobacterium(14 %).In the BFT group,Firmicutes in the early flocculation stage were the dominant flora,with the abundance reaching 86 % and the rest less than 10 %.In the late stage,it was 43 % Chlorofiexi,26 % Proteobacteria and 12 % Bacteroidetes.In terms of genus level,Bacillus was the dominant species at the initial stage of cultivation,reaching 86 %,while the Bacillus species abundance dropped to 3 % at the end of cultivation,with 40 % of norank-f-caldilineaceae and 22 % of Flavobacterium.The dominant Bacteria in the intestinal tract of RAS group were Actinobacteria(20 %),norank-o-jg30-kf-cm45(25 %),Proteobacteria(35 %),Bacillus(16 %)and Cetobacterium(13 %).In the biological filter of RAS group,Nitrospira was found to be the dominant Bacterium at the initial stage of cultivation,with the enrichment rate of 10 %,the ratio of Nitrospira to 1 % at the later stage of cultivation,and the most dominant Bacterium was 27 % of the abnormal coccus.The results showed that the functional Bacteria performing the autotrophic nitrification process in the RAS and BFT systems were Nitrosomonas and Nitrosospira,and the abundance decreased due to low temperature,which affected the nitrification effect of the biological filter in the RAS system.Compared with RAS mode,BFT mode has a higher abundance of beneficial intestinal flora,which can improve the digestive capacity,and promote the healthy growth of fish.3.Study on the cultivation of tilapia large-sized fingerlings in BFT and RASIn order to study whether RAS and BFT system can make tilapia reach the requirement of rapid growth after the end of overwintering period,the experiment was divided into RAS group and BFT group for 67 days of cultivation,and the water quality and the growth of fish in the cultivation process were measured.The results showed that the weight gain rate and specific growth rate of RAS group and BFT group were 870.69 ± 33.25 %,3.39 ± 0.05 % / d,659.47 ± 62.84 % and 3.02 ± 0.13 % / d,respectively.RAS group was significantly higher than BFT group.In terms of water quality control,RAS group of ammonia nitrogen and nitrite from the early stages of breeding to the end of the experiment are maintain in low level,while the BFT group at an early stage of ammonia nitrogen and nitrite has a tendency to rise,peak is 4.53 ± 0.72 mg/L and 6.68 ± 1.8 mg/L,respectively,in 3 days and 6 world down to a lower level,respectively,and present a tendency of the continued accumulation of nitrate in the two groups.The results show,the growth rate of tilapia cultured in RAS system is higher than that of BFT system,but the survival rate is lower than that of BFT system,and the breeding cost is higher than that of BFT system;RAS system is slightly better than BFT system in water quality control.4.Study on the effect of feeding frequency of Bio-floc Technology(BFT)system on tilapia cultureIn order to study the optimal bait frequency of tilapia in the BFT system,this experiment was carried out.The experiment was divided into three groups: group A(2 times /d),group B(3 times /d)and group C(4 times /d).Three parallel experiments were carried out in each group.There were no significant differences in the weight gain rate,specific growth rate and bait coefficient between groups A,B and C,but the weight gain rate and specific growth rate of group A were slightly higher than the other two groups,and the bait coefficient was also lower than the other two groups.In terms of water quality,ammonia nitrogen and nitrite were increased in the three groups at the early stage,and the peak values of the two indicators in group C were significantly higher than those in groups A and B,31.65 ± 5.65 mg/L and 6.88 ± 1.86 mg/L,respectively.There was no difference in the growth rate of total solid suspended solids(TSS)between groups A,B and C,which finally reached 1815.67 ± 50.95,1846 ± 89.82 and 1880.67 ± 39.37 mg/L,respectively.The results showed that feeding frequency in BFT system had no significant effect on fish growth,water quality and flocs stability,but feeding frequency twice a day had slight advantages over other two groups. |
PDF Full Text Request