| Pond fish culture is an important aquaculture model in China. The farmers through the high stocking density and fed large quantity bait to improve farming production and increase economic gains. There are large amounts of N, P and other nutrients in the bait,but only a few were absorbed by fish, most of the nutrients were accumulated in the bottom or dissolved in water, the excess nutrients beyond the water body self-purification ability became a pollution, the major pollutant element are N and P in aquaculture ponds.Phytoplankton are important primary producers in pond water, Cyanophyta can easily form blooms due to its own advantages in summer and autumn months, but some of Cyanophyta species have poor palatability and low in nutrition, some species even produce algal toxins. On the contrary, some Bacillariophyta species are more suitable to be natural food for fish, they can also improve the water quality. Therefore, in the regulation of phytoplankton in pond, people hope to increase Bacillariophyta species.In order to find a new way to improve the water quality in pond and adjust the phase structure, this study adding a new biological nutrient which named Nualgi into fishponds to research the change of the water quality and phytoplankton community.The results are as follows:1.The optimum concentration of Nualgi explored: From July 1 to July 15 in 2015,the optimum concentration of biological nutrient was studied in the laboratory, the test was divided into 6 groups, each group consisted three parallel and adding different concentration of Nualgi respectively. It showed that the Synedra grew best when adding 3.6×10-3μl Nualgi into 30 ml pond water. So the optimum concentration of Nualgi is 0.12ml/m3.2. Compared the effect of different culture medium on algae growth: From July20 to August 3 in 2015, the effect of the growth about Synedra and Navicula were performed in the laboratory. Experimental results showed that: The two diatom grewbest in the groups of CSI and the pond water which adding optimum concentration of Nualgi. To provide a theoretical basis of outside use about biological nutrient. This proved that Nualgi can take the place of CSI in diatoms expand training.3. In order to study the effects of Nualgi on water quality and phytoplankton in fishpond, we conducted continuous and regular surveys on the phytoplankton community and the water quality indexes in 4 groups. The 4 groups were a Nualgi group(M1), an algae group(M2), a Nualgi and algae group(M3), a control group(C).The results showed that the pH, DO, TN, TP were no remarkable difference between the 4 groups(P>0.05), group M1 and M3 were remarkable lower than group C(P<0.05)means Nualgi can reduce IP in water, adding Nualgi or Dominant algae can both reduce NH4+-N, NO2--N and CODMn to adjust water quality, so group M1, M2 and M3 were both remarkable lower than group M2 and C(P<0.05). During the test, we identified186 species that belonged to 7 phyla and 109 genera. 86 species were Chlorophyta, 48 were Bacillariophyta, 27 were Cyanophyta, 17 were Euglenophyta, 3 were Dinophyta,3 were Cryptophyta and 2 were Chrysophyta. Adding diatom algae or Nualgi both can promote the growth of Bacillariophyta and restrain the growth of Chlorophyta and Cyanophyta. In the test, Melosira granulata became the dominant algae in group M1,M2 and M3 but without group C, Coelastrum microporum and Crucigenia tetrapedia are the dominant algae in group C only, Scenedesmus quadricauda became the dominant algae in group M1, M2 and C. There was no remarkable difference between the 4 groups about the diversity index, the Shannon-Weiner index were all above 2.00 which showed that the species diversity is abundant. |
PDF Full Text Request