| Bio-floc technology (Biofloc Technology,BFT) is a technique of enhancing waterquality in health aquaculture through balancing carbo n and nitrogen in the system,heterotrophic microorganisms on the controlled conditions form to bioflocs.Bioflocsincluding bacteria, organic matter, protozoa and algae, which can improve waterquality, save feed and promote animal immunity. In this thesis we studied the bioflocculture technology in Crucian carp culture system.The experiment was conducted toinvestigate the effects on growth, survival rate, water quality, non-specific immunityand digestive enzyme activity of Crucian carp. This study includes the following twocontents:1Explore the culture and functions of biofloc in high density and zero water exchangefarming systems of Crucian CarpA60-day experiment was conducted to evaluate the effects of the bioflocstechnology（BFT）on growth, survival and water quality of the Crucian Carp(Carassius auratus）in high density and zero water exchange farming systems. Thebioflocs treatment and control were managed in six rectangle aquarium. The bioflocswere developed in the BFT treatment using glucose as a carbon source and maintain aC:N ratio of20:1. Eighty juvenile Crucian Carp(average5.01g) were stocked per tankand BFT treatment and the control was tested in three replicates. The results showedthat: the training process, the water temperature in the range of25-32°C, DO controlover5mg/L, pH in the range of5.09-7.99. The observed biofloc morphology structure,biofloc is relatively small, it consist of residual feed,bacteria, organic matter,protozoaand algae. most biofloc diameter0.1-1.0mm. At the end of the experiment, survivalrates of the fish were100%, with no significant differences among the two groups(P>0.05); and the specific growth rate of the fish in bioflocs treatments weresignificantly higher(P<0.05)than that obtained in the control. The feed conversion rate of the fish in bioflocs treatments was significantly lower than that in the control(P<0.05). In the trial period, the concentration of ammonia-N in control in range of0.43-5.14mg/L, and in biofloc treatments are0.47-1.31mg/L,there was no differencebetween the two groups. The nitrite-N concentration in control in range of0.14-0.78mg/L, and in biofloc treatments are0.01-0.74mg/L, there was no differencebetween the two groups before30days, it is significantly lower than that in thecontrol after30days. The nitrate-N concentration in control in range of6.07-33.73mg/L, and in biofloc treatments are1.2-8.23mg/L, there was no differencebetween the two groups before7days, it is significantly lower than that in the controlafter7days.2Effects of bioflocs on growth performance, water quality digestive enzyme activityand non-specific immune of crucian carp manipulating C/N ratioA70-day feeding experiment was conducted to investigate the effects ofpromoted bioflocs on growth performance, digestive enzyme activity and non-specificimmune of crucian carp (average2.71±0.01g) in culture tanks. Two bioflocstreatments and one control were evaluated: Bioflocs based tanks with two levels ofC/N ratio (15,20) by addition of carbohydrate referred to as ‘CN15’ and ‘CN20’, andclear water tanks without addition of carbohydrate re ferred to as ‘Control’. Eachgroup consisted of quadruplicate tanks (300L) and each tank contained100fish. Theresults show: The survival rates in the range of95-98%, with no significantdifferences among the three groups (P>0.05). With the increase of C/N, the specificgrowth rate and protein efficiency ratio show an upward trend, there is no significantdifference between the three groups (P>0.05), and feed conversion ratio show adowntrend，there is no significant difference between the three groups (P>0.05). In theexperiments, the CN20, the CN15and the concentration of ammonia-N of the controlgroup are respectively in0.23to0.87mg/L,0.21to0.73mg/L and0.23to0.69mg/L.Each concentration of ammonia-N was slowly rising, but there is no significantdifference between these groups (P>0.05). The group of CN20, CN15and theconcentration of nitrite-N in the control group were0.01-0.64mg/L、0.04-0.62mg/L、0.08-0.61mg/L. The concentration of each group was reduced after the first rise trend,there are the significant differences between groups in terms of aquaculture for7days(P<0.05). The group of CN15, CN20and the concentration of nitrate-N of the controlgroup are in0.17-7.67mg/L、2.93-13.2mg/L、8.17-55.66mg/L, each concentration of nitrate-N are in the trend of increasing. Two biofloc groups crucian carp intestinalamylase activity was significantly higher (P<0.05) was significantly higher than in theCN20and CN15(P<0.05). The lipase and protease activity of intestinal in two bioflocgroups was significantly higher than that in the control group (P<0.05), but there wasno significant difference (P>0.05) between the two biofloc treatments. Superoxidedismutase activity increased with the increase of the C/N ratio, an upward trend, twobiofloc groups superoxide dismutase activity was significantly higher than that of thecontrol group (P<0.05), C/N20significant higher than the C/N15(P<0.05). Controlgroup, alkaline phosphatase activity was significantly higher than the two bioflocgroups (P>0.05), there is no significant difference between the two biofloc groups(P>0.05). With the C/N ratio increases, the biofloc significantly increased acidphosphatase activity, two biofloc groups was significantly higher (P>0.05), C/N15was significantly higher than the C/N20. |
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