| Eels were mainly cultured in the intensive ponds and the earth ponds in China at present.We studied the high-density fingerlings breeding, high-density culturing and disease control andprevention of A. japonica and A. rastrata by the technique of recirculating aquaculture in orderto develop a new mode of eel culture. The main results showed as follows:1. The Experiment of Eel Fingerlings Breeding. A. japonica and A. rastrata fingerlingswere bred by the water recirculating system. A. japonica fingerlings were first feedingLimnodrilus hoffmeisteri44days and then feeding compound diet26days by the waterrecirculating systems which carry the capacities of1.0and1.5m3. The stocking densities of A.japonica fingerlings were more than9600fish/m3in feeding L. hoffmeisteri and more than9500fish/m3in feeding compound diet. A. rastrata fingerlings were first feeding L. hoffmeisteri69days by the water recirculating systems which carry capacities of1.0and1.5m3and thenfeeding compound diet42days by the ones which carry capacity of1.0m3. The stockingdensities of A. rastrata fingerlings were more than10100fish/m3in feeding L. hoffmeisteri andmore than4382fish/m3in feeding compound diet. The temperature of water was27～30℃, andthe pH was5.4～6.2. The water quality of DO, NO2--N and NH3-N of A. japonica and A.rastrata fingerlings were4.71～6.10mg/L and6.38～6.55mg/L,0.99～3.40mg/L and0.37～0.78mg/L,20.00～24.55mg/L and2.53～13.97mg/L, respectively, during the experimentalperiod. The results showed the feeding, behavior and growth of A. japonica and A. rastratafingerlings were all normal. The survival rates (SR) of A. japonica and A. rastrata fingerlingswere all above95.02%. The specific growth rates (SGR), feeding rates (FR) and feed conversionratioes (FCR) of A. japonica and A. rastrata fingerlings were more than7.08±0.09%/d and4.82±0.06%/d,20.47±0.19%and12.61±0.02%,4.92±0.09and4.67±0.01, respectively, duringthe period of feeding L. hoffmeisteri. And the SGR, FR and FCR of A. japonica and A. rastratafingerlings were more than2.30±0.19%/d and1.69±0.05%/d,2.90±0.27%and2.84±0.02%,1.28±0.01and1.76±0.06, respectively, during the period of feeding compound diet. Thefingerlings breeding effect of A. japonica and A. rastrata in the water recirculating systemswhich carry capacity of1.5m3were better than in the ones of1.0m3by the comparison of theSGR, FR and FCR. But there were no significant difference on the SGR, FR and FCR betweenthe water recirculating systems which carry capacity of1.5m3and the ones of1.0m3.2. The Experiment of Eel Culture. A. japonica and A. rastrata were cultured by the water recirculating systems which carry capacity of1.0m3. The stocking densities of A. japonica and A.rastrata became bigger with the growth of the eel size. The stocking density of A. japonicawhich size3.84～205.51g were7.60～48.41kg/m3, and the stocking density of A. rastrata whichsize2.43～240.54g were9.30～50.85kg/m3. The temperature of water was26～30℃, and thepH was5.4～6.2. The water quality of DO, NO2--N and NH3-N of A. japonica and A. rastratawere6.48～6.62mg/L,0.47～0.81mg/L and1.68～2.68mg/L, respectively, during theexperimental period. The results showed the feeding, behavior and growth of A. japonica and A.rastrata were all normal. The survival rates (SR) of the various sizes of A. japonica and A.rastrata were above97.65%and91.37%. The SGR and FR of A. japonica and A. rastratabecame smaller and the FCR became bigger with the growth of eel size. The SGR, FR and FCRof A. japonica and A. rastrata were0.30～2.32%/d and0.29～1.10%/d,0.58～2.70%and0.54～1.44%,1.33～1.98and1.34～2.02, respectively.3. The Experiment of Eel Culture on the Different Stocking Density. A. japonica and A.rastrata of the similar size and the same experimental time were cultured on the two kinds ofstocking density by the water recirculating systems which carry capacity of1.0m3. The highstocking density of A. japonica and A. rastrata were bigger1.17～1.39times and1.08～2.45times than the low ones, respectively. We had carried on the date analysis of A. japonica by thepaired sample analysis, and the date analysis of A. rastrata by one-way anova. The resultsshowed the SGR and FR of the low stocking density of A. japonica were significantly biggerthan the ones of the high stocking density (P<0.05). There were no significant difference on theFCR between the low and the high stocking density of A. japonica (P>0.05). The SGR of thelow stocking density of A. rastrata were significantly bigger than the ones of the high stockingdensity when the high stocking density were bigger1.25times than the low ones, and the FCRwere significantly smaller than the ones of the high stocking density too (P<0.05). The FR of thelow stocking density of A. rastrata was bigger than the ones of the high stocking density. Therewere no significant difference on the SGR, FR and FCR between the low and the high stockingdensity of A. rastrata when the times of the low and high stocking density were lower than1.25(P>0.05). The SGR and FR of the low stocking density of A. rastrata were bigger than the onesof the high stocking density, and the FCR were smaller than the ones of the high stockingdensity.4. The Experiment of Disease Control and Prevention. We studied the disease controland prevention of A. japonica and A. rastrata in the recirculating aquaculture on the immersiondisinfection by the filtered seawater. The disease prevention measures in the recirculatingaquaculture were that keeping eels in a regular immersion12h (once a week) by the filteredseawater of8salinity. When the disease or death was happened, keeping eels in an immersion 1～3d by the filtered seawater of8salinity; or keeping eels an immersion30min by the filteredseawater of20～25salinity then keeping eels an immersion by the filtered seawater of8salinity(repeat3d). The results showed that the preventive effect was good. It could reduce theeel death and restore the eel feeding by the treatment measures. And it indicated that thetreatment effect was good.The results showed that the high-density culture effect of A. japonica and A. rastrata bythe new mode of recirculating aquaculture was good. The culture effect of A. japonica was betterthan those of A. rastrata by the comparison of the SGR, FR and FCR whether during the periodof fingerlings breeding or during the period of culture. The SGR and FCR of A. japonica and A.rastrata were similar to the ones of traditional culture which in the intensive ponds. This newmode of eel culture has many advantages, such as high-density, high-SR, energy-saving,emission reduction, non-residue and so on. The technique of disease control and prevention inthe recirculating aquaculture on the immersion disinfection by the filtered seawater couldeffectively prevent and control the disease, and it was non-residue, no side-effect and low-cost. |
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