| Monopterus albusalso known as eel,is an important economic fish in China and also one of the well-known freshwater aquatic products.Monopterus Albus is favored by the vast number of consumers for its high nutritional value and medical function,however,due to overfishing and deterioration of ecological environment,wild resources of Monopterus Albus cannot satisfy the market demand.Additionaly,farming model and artificial breeding technology of Monopterus Albus are still under development.Therefore,in this study,effects of stocking density and cage size on survival rate,growth of Monopterus Albus and water qualitywere explored,form which,the optimal stocking density and cage size for eel culture are expected to be found,and thereby to increase its economic efficiency.The results showed as follows:(1)Stocking Density: In this subproject,we aimed to find the suitable stocking densities by setting 6 groups(3 replication for each)with different stocking densities,which were 5 tail/m2(SD1),10 tail/m2(SD2),15 tail/m2(SD3),20-tail/m2(SD4),25-tail/m2(SD5)and 30-tail/m2(SD6)respectively.Body length of eel is(28.65±0.52)cm,while weight is(21.73±2.24)g.After feeding for 60 d,the growth performance,survival rate of eel and water quality were measured.The results indicated that stocking density had significant effects on growth performance and survival rate of eel.In group SD5,the final weights were the highest(60.88g),which was significantly higher than that in other groups(P<0.05).While in group SD1,the final weights were the lowest with only 37.22 g,which is lower than that in other groups significantly(P<0.05).Specific growth rate increased and then decreased along the increase of stocking density,in group SD5,the data was the largest,and the variance was significant when compared with other groups except SD4.Survival rate decreased with the increase of stocking density,data in SD3 was the highest(95%),which is remarkably higher than that in other groups.The hepatosomatic indexes(HSI)increased significantly after 60 d feeding.For physicochemical factors,pH and dissolved oxygen(DO)decreased through the experiment,while the concentration of NO2--N,NO3--N and NH4+-N increased.At the mid and end of the experiment,pH and DO in groups with higher stocking density were lower than that in lower stocking density,while the trends for NO2-N,NO3-N and NH4+-N were opposite.As for profit analysis,highest economic benefit was gained in SD5 with 48.68% for the rate of return.A conclusion could be drawn that stocking density affected the growth of eel and water quality noticeably from foresaid results,and the optimal stocking density is 25 25-tail/m2,followed by 20-tail/m2.(2)Cage Size: In order to find the optimal cage size,five different cage size(area)were set,which were 1m2(A1),1.5m2(A2),2m2(A3),4m2(A4),6m2(A5)with 3 replications for each.After 60 d feeding,growth performance,survival rate and water quality were measured.The results showed that,the final weight in A5 was the highest with 53.03 g,and there was insignificant variance between A5 and other groups.Along the increase of cage size,specific growth rate showed an increasing trend,that in A5 was the largest,but insignificant variance was observed between groups.Growth rate decreased along the increase of cage size.Growth rate in A1 was the highest with 90%.The hepatosomatic indexes increased noticeably through the experiment,that in A5 was the highest(6.14%).pH and dissolvedoxygen decreased through the experiment,while increased for NO2--N,NO3--N and NH4+-N.At the mid and end of the experiment,pH and DO in groups with larger cage size were lower than that in smaller cage size,while the trends for NO2-N,NO3-N and NH4+-N were opposite.As for profit analysis,highest economic benefit was gained in A4 with 28.76% for the rate of return.A conclusion could be drawn that stocking density affected the growth of eel and water quality noticeably from foresaid results,and the optimal cage size is 4m2(2m×2m×1.2m). |
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