Screening Of Planktonic Microalgae And Bacteria Metabolism Inhibitors And Uptake Of Dissolved Nitrogen In Prawn Pond

Intensive farming is the main form of farmed shrimp, In the process of shrimpfarming, as to the accumulation of residual feed and shrimp excrement in aquaculturewater, eutrophication has become the major pollution phenomenon of intensiveshrimp farming systems, toxic nitrogenous compounds are major pollutants in prawnponds and has obvious toxic effects on shrimp. Nitrogen absorbing of planktonicalgae and bacteria is an important way to reduce the nitrogen pollution in the waterenvironment. In this paper, which the high prawn pond was studied, we used thestable isotope15N as a marker, antibiotics as inhibitors to interrupt the metabolicprocesses of planktonic algae and bacterial, studied the absorption rate, selective andkinetics of dissolved nitrogen on planktonic microalgae and bacteria, and thendiscusses the contribution on the absorption of dissolved nitrogen of planktonic algaeand bacteria in prawn ponds, the results as follows:1. Different concentrations of CHI can significantly inhibit the growth andmetabolic of Oocystis borgei and Cyclotella striata, and reduce the content andmetabolic intensity of chlorophyll a. When the incubation time is2h, the optimalconcentration of CHI inhibiting the metabolism of Oocystis borgei and Cyclotellastriata is100mg/L.2. Penicillin, streptomycin and penicillin-streptomycin can significantly inhibitthe growth and metabolism of bacterial in prawn pond. Penicillin-streptomycin caneffectively inhibit the proliferation of bacteria, when the incubation time is2h,penicillin-streptomycin concentration of100mg/L, the number of bacteria decreased100%compared to the control group.3. During shrimp culture, dissolved nitrogen of post-breeding in prawn pondswas significantly higher than the prophase and interim. Prophase in the breeding totaldissolved nitrogen content in a low level with an average of0.57mg/L; Then the totaldissolved nitrogen content along with the rise, arrived about1.29mg/L averagely ininterim, which was significantly increased, up to2.1mg/L at late breeding, Eutrophication in the late exceeds the threshold, the eutrophication of water pollutionis a major phenomenon of shrimp farming.4. There are differences on the dissolved nitrogen absorption rate of microalgaeat the prophase, interim and Late stage. NH4+-N uptake rate of planktonic microalgaeat the late stage of breeding up to maximum is0.762μmol/(L·h), early, which is the2.1times and3.4times of prophase and interim, respectively. NO3--N uptake rate upto maximum at the interim of breeding is0.127μmol/(L·h), which is the2.7times and2.0times of prophase and late stage, respectively. While Urea-N uptake rate up tomaximum at the interim of breeding is0.361μmol/(L·h), which is the2.6times and2.2times of prophase and late stage, respectively.5. NH4+-N uptake rate of bacterial at the prophase of breeding up to maximum is0.429μmol/(L·h), early, which is the1.5times and2.2times of interim and late stage,respectively. NO3--N uptake rate up to maximum at the interim of breeding is0.739μmol/(L·h), which is the2.3times and2.0times of prophase and late stage,respectively. While Urea-N uptake rate up to maximum at the prophase of breeding is0.361μmol/(L·h), which is the2.1times and2.6times of interim and late stage,respectively.6. The selective of dissolved nitrogen with different in different breeding periodby planktonic algae and bacteria. At the early and late stage, planktonic microalgaepreferentially absorbed NH4+-N, and showed preference on NH4+-N, and at theinterim, which priorities to absorbe Urea-N. Bacteria in the early and late arepreferentially absorbed NH4+-N, showed preference on NH4+-N, while themedium-term priorities absorb NO3--N.7. NH4+-N uptake contribution ratios of planktonic algae are0.9and0.8timesbacteria in the the prophase, interim of breeding, indicating that planktonic algaeand bacteria share the equal strength to absorb NH4+-N. In the latter part of foraquaculture, NH4+-N uptake ratio of planktonic algae is four times the contribution ofbacteria, and NH4+-N was mainly absorbed by planktonic algae.8. The planktonic microalgae and bacteria the kinetic parameters of dissolvednitrogen absorption in prawn pond reflected that: The ratio of maximum absorptionrate of planktonic microalgae for NH4+-N was significantly higher than NO3--N andUrea-N; affinity (Ks) performance of Urea-N>NH4+-N>NO3--N, and planktonicmicroalgae have the ability to use Urea-N. Bacteria NH4+-N, NO3--N, the maximumspecific absorption rate of Urea-N (Vmax) averages were:2.772h-1,2.200h-1,3.588 h-1; affinity of three dissolved nitrogen (Ks) performance of NO3--N>NH4+-N>Urea-N,nitrate bacteria more easily absorbed.These results demonstrated that at different times in the process of shrimpfarming, planktonic algae and bacteria exhibit different competitive to dissolvednitrogen absorption; Planktonic microalgae can absorb the NH4+-N and Urea-N morecompetitively, while bacteria is NO3--N. Of these research results provide theoreticalsuppor on the use of planktonic algae and bacteria on removal of toxic nitrogencompounds and improval the water quality in the intensive shrimp farming systems.