| Recirculating Aquaculture System(RAS)is a kind of resources saving and environment friendly aquaculture mode,in which aquaculture waste water can be purified and recyclable by water treatment.It has the advantages of water saving,land saving,high yield,less disease,product quality safety,environmental friendliness,and aquaculture is not limited by regional climate.It is an important way to achieve sustainable development of aquaculture.In order to gain the full advantages of RAS and achieve high yield and high efficiency,the supporting aquaculture techniques of RAS must meet the requirements of the biological characteristics of the object culture species.In this study,Anguilla rostrata from South America was taken as the experimental object,and the closed RAS designed and established by our research group was used to study the supporting aquaculture techniques of Anguilla rostrata.The results may provide guidance for the extension and application of the advanced supporting eel aquaculture techniques of RAS and promote the progress of recirculating aquaculture technology.(1)Studies on Oxygen Consumption Rate(ROC),Asphyxial Point(AP)and Optimum Water Temperature Range(RT)of Anguilla rostrata and LC50 and SC of Non-Ionic Ammonia(NIA)and Nitrite in Water.The results showed that diurnal variation of the oxygen consumption rate of Anguilla rostrata,the oxygen consumption rate during the daytime was(86.46±38)mg/(kg h),at night(123.58±23)mg/(kg h),and there was significant difference between them(P<0.05).At the range of 15～30℃,the oxygen consumption rate was gradually increased with water temperature up,the relation formation between oxygen consumption rate and water temperature as y=-0.1316x2+9.4507x-13.712,(R2=0.9993).The oxygen consumption rate decreased with body mass up,but the amount of oxygen consumption increased with body mass up.The relationship between oxygen consumption and body weight was y=0.2321x0.8334(R2=0.9979).At the water temperature of 25℃,the asphyxial point decreased with fish mass up.Average eel individual weight at 10g,40g and 160g,the dissolved oxygen concentration at the suffocation point of eel was(1.18±0.05)mg/L、(0.91±0.1)mg/L and(0.46±0.06)mg/L,respectively.The optimum water temperature range for Anguilla rostrata was 13～29℃,however 25～29℃ was the optimum water temperature range for good growth,and in a certain range of short time low water temperature or high water temperature environment to its damage was reversible in some extent.The LC50 and SC of non-ionic ammonia in water for Anguilla rostrata was 12.22 mg/L and 1.22 mg/L respectively,and the LC50 and SC of nitrite nitrogen was 61.68 mg/L and 6.17 mg/L respectively.(2)L9(34)orthogonal trial design was used to conduct Anguilla rostrata fingerling recirculating aquaculture experiment.The effects of four kinds of aquaculture techniques on the eel production effect and water quality improvement were studied,including the daily water cycle times(3 times,6 times and 9 times),the concentration(0%,0.25%,1%)of Chinese traditional polysaccharide compound added to feed,the density of biofilm water-cleaning grille(0%,10%,20%),and the proportion of soybean oil added to feed(3%,6%,8%).During the culture period of 180d,the results showed that the water cycle utilization rate of the RAS reached 95%;the survival rate of the elvers was 97.3%,the FCR(feed conversion ratio)was 1.49,the SGR(specific growth rate)was 1.24%/d,and the WGR(weight gain rate)was 844.22%.No parasitic or bacterial diseases occurred;the concentration of water TAN(total ammonia nitrogen)was(0.573 ±0.35)mg/L,and the NO2-N was(0.110±0.071)mg/L,both less than the safe concentration of ammonia nitrogen and nitrite to Anguilla rostrata,which met the requirements of its biological characteristics.According to the comprehensive evaluation of the culture effect and water quality,the optimal combination of aquaculture techniques was as follows:6 daily cycles of water,20%density of biofilm water-cleaning grille,6%soybean oil added to the feed and 1%polysaccharide compound added to the feed.Under the conditions of the optimal combination,the growth rate of Anguilla rostrata was fast,FCR was low,water quality was good and comprehensive culture effects was the best.(3)L9(34)orthogonal trial design was used to conduct Anguilla rostrata yellow eel recirculating aquaculture experiment.The effects of four kind of aquaculture techniques on the eel production effect and water qualitty improvement were studied,including the light intensity(10 lx,80 lx,160 lx),the frequency(2 times,3 times,4 times)of daily feed feeding,the concentration(0%,0.5%,2%)of Chinese traditional medicine Pulsatilla compound added to feed,and the frequency(never,Once a day,Once every 5 days)of cleaning operations in the aquaculture barrels.During the culture period of 150d,the results showed that the water cycle utilization rate of the RAS reached 92.5%;the survival rate of the elvers was 98.2%,the FCR was 1.54,the SGR was 0.72%/d,and the WGR was 192.9%.No parasitic or bacterial diseases occurred;the concentration of water TAN was(1.037 ± 0.35)mg/L,and the NO2-N was(0.070±0.031)mg/L,both less than the safe concentration of ammonia nitrogen and nitrite to A nguilla rostrata,which met the requirements of its biological characteristics.According to the comprehensive evaluation of the culture effect and water quality,the optimal combination of aquaculture techniques was as follows:light intensity 160 lx,4 times of daily feed feeding,0.5%pulsatilla compound added to the feed and never cleaning the aquaculture barrels.Under the conditions of the optimal combination,the growth rate of Anguilla rostrata was fast,FCR was low,water quality was good and comprehensive culture effects was the best. |
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