| Turbot(Scophthalmus maximus) is favored by the market for its many characteristics such as thorny flesh,delicious meat,and rich nutrition.At present,turbot breeding mostly uses factory farming for high-density aquaculture.Ho wever,the shortcomings of low breeding efficiency and large energy consumption and emissions have led to the development of the breeding model to factory recirculating aqua culture.The recirculating aquaculture system has high requirements on the oxygenation device,and the current aerators generally have problems such as low oxygen concentration and instability.It is necessary to apply a new device.Molecular sieve pressure swing adsorption(PSA)oxygen generators have been maturely used in other industries such as medicine.Based on the technology,a new type of oxygen enhancing device with high efficiency and resistance to salt-alkali corrosion can be developed according to the characteristics of the marine environment.In this paper,a new type of six-tower Vacuum Pressure Swing Adsorption(VPSA)oxygen generator was applied to the recirculating aquaculture system of turbot for the first time.In the common culture of turbot(3kg/m~3),using air aeration as a control,the effects of two aeration modes on the growth,metabolism and water quality of turbot were investigated under the same dissolved oxygen concentration(7mg/L).In the high-density culture of turbot(10.5kg/m~3),the effects of two dissolved oxygen concentrations(7mg/L and 10mg/L)on the growth,metabolism and water quality of turbot were compared.The main experimental results are as follows:1.The effect of VPSA oxygen generator on the growth and development of turbot.(1)In the comparison of the pure oxygen group and the air group in the normal breeding density of turbot(3kg/m~3),after 8 weeks of culture,the growth rate of the body length and body weight of the pure oxygen group were higher than those of the air group,and the pure oxygen group and the air group had higher growth rates than the air group.The survival rates reached 99.6%and 98.9%,respectively.There was a significant difference in the body length of turbot at the 8th week(air group:10.59-14.15cm,pure oxygen group:10.38-15.59cm,P<0.05).It shows that with the same concentration of oxygen,pure oxygen enrichment is beneficial to the growth of turbot to a certain extent compared with air enrichment.(2)In the comparison of turbot high-density culture(10.5kg/m~3)7mg/L and 10mg/L pure oxygen group,the body length and weight growth rate of 10mg/L pure oxygen group were higher than 7mg/L pure oxygen group after 8 weeks of culture,the survival rates of 10mg/L and 7mg/L pure oxygen groups reached 93.3%and 89.2%,respectively.There was a significant difference in turbot body weight from the 6th week(7mg/L pure oxygen:203.42-269.49g,10mg/L pure oxygen:202.15-287.88g,P<0.05),and the difference began to increase with this time.It shows that the high concentration of pure oxygen is beneficial to the growth of turbot.2.The effect of VPS A oxygen generator on turbot enzyme activity.(1)In the comparison of turbot common breeding density(3kg/m~3)pure oxygen group and air group,α-amylase activity continued to increase with the advancement of breeding time,and there was a significant difference between the two groups since 4th week(air group:5.82-13.21 U/mgprot,pure oxygen group:6.63-15.46U/mgprot,P<0.05);in the activities of pepsin,trypsin and SOD,there was little difference between the two groups(P>0.05);in the activity of lipase,there was a significant difference between the two groups in the 8th week(air group:7.38-11.03U/mgprot,pure oxygen group:8.84-6.88U/mgprot,P<0.05).Weight differences(air group:7.14-7.12U/mgprot,pure oxygen group:6.24-8.46U/mgprot,P<0.05);indicating that pure oxygen aeration can stimulate the appetite of turbot to a certain extent compared with air aeration.(2)In the comparison of turbot high-density culture(10.5kg/m~3)7mg/L and 10mg/L pure oxygen groups,there was little difference in the activities of α-amylase,trypsin,lipase and CAT between the two groups(P>0.05);pepsin continued to decrease with the advancement of culture time,and there was a significant difference between the two groups from the 4th week(7mg/L group:30.03-21.23U/mgprot,10mg/L group:35.08-27.68 U/mgprot,P<0.05);in SOD activity,the enzyme activity of the two groups did not change much with the breeding time,and there was a significant difference between two groups at 8th week(7mg/L group:32.12-30.62U/mg prot,10mg/L group:35.02-36.49U/mgprot,P<0.05).It indicated that high concentration of pure oxygen could help turbot to digest and resist stress to a certain extent,promote growth and reduce mortality.3.The influence of VPSA oxygen generator on the water quality of turbot.(1)In the comparison between the pure oxygen group and the air group of turbot in ordinary breeding density(3kg/m~3),the contents of ammonia nitrogen and nitrate were generally increased during the experiment.By the end of the 8th week,there was a significant difference in ammonia nitrogen content between the two groups(air group:0.12-0.35mg/L,pure oxygen group:0.12-0.44mg/L,P<0.05);nitrite content from the first week There was a very significant difference(air group:0.23-0.38mg/L,pure oxygen group:0.02-0.04 mg/L,P<0.01);there was no significant difference in nitrate and phosphate content(P>0.05).It shows that pure oxygen can reduce the concentration of toxic nutrient in salt water,which is helpful for the growth of turbot.(2)In the comparison of turbot high-density culture(10.5kg/m~3)7mg/L and 10mg/L pure oxygen groups,ammonia nitrogen was always on the rise during the experiment.At the seventh week of the experiment,there was a significant difference(air group:0.42-0.56mg/L,pure oxygen group:0.47-0.64mg/L,P<0.05),and the nitrite content was extremely low throughout the experiment.The contents of nitrate and phosphate were relatively stable,and there was no significant difference among the three(P>0.05).It shows that high concentration of pure oxygen can reduce the concentration of ammonia nitrogen and reduce the mortality of turbot to a certain extent.This paper studies the application of a new type of oxygenation device in the recirculating aquaculture system of turbot 10mg/L pure oxygen can increase the growth rate of turbot,reduce the mortality and the concentration of toxic nutrients,and has a high application prospect in the direction of high-density breeding. |
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