| Increasingly serious eutrophication problem has an adverse impact on development of aquaculture and fishing as well as water ecological environment. Hypophthalmichthys molitrix is the main cultured fish in Shanxi province, distributed in multiple reservoirs and ponds across Shanxi province. So, it is necessary to explore the relationship of fish breeding and phytoplankton. This experiment has carried on exploration including the following content:the selectivity of H. molitrix for food in water area of Shanxi province, influence on the algal community structure of high and low breeding density in the water, influence on several kinds of enzyme activities in fish body of high and low breeding density. On this basis, effects on phytoplankton and water quality in fishponds of micropore bottom aeration method have been studied, showing that it can serve as complement or emergency measures in fish-breeding. The results of the study are as follows:1. The composition of phytoplankton were investigated in four reservoirs from Shanxi, meanwhile, the fishes were dissected the contents in different intestine parts were collected. The results indicated that the digestion of H. molitrix to different division of phytoplankton was distinguishing. Overall, H. molitrix was easier to digest the unicellular and small colony phytoplankton, but difficult to digest the large colony types, especially those with abundant gelatin. The species of Chrysophyta and Pyrrophyta were the easiest to digest, and those of Chlorophyta, Bacillariophyta and Euglenophyta were secondary, whereas the blue-green algae were more difficult to digest correspondingly.2. Two experimental groups (each including four ponds) were set in Wenliushui excellent fish breeding grounds in Yongji, Shanxi province, which represent low and high Hypophthalmichthys molitrix breeding density of 21.2 g·m-3and 42.4 g·m-3 respectively. Based on the changes of dissolved oxygen in water for a few months, the results showed that dissolved oxygen of high density breeding ponds was higher than that of low density ponds, and the water quality is better. Based on the identification and count of total alage and Cyanophyta cell abundance for six months, the results showed that in the first three months, breeding of H. molitrix density has little effect on these two indexes. But three months later, the total alage and Cyanophyta cell abundance in high breeding density ponds were obviously lower. Based on dominant phytoplankton species identification in different breeding density ponds for six months, the results showed that in the first three months H. molitrix breeding density has little effect on dominant phytoplankton species. But three months later, the dominant species of low density ponds showed cyanobacteria presented, and Microcystis flos-aquae appeared in the July. But this phenomenon had not occurred all the time in high density ponds. And Chroococcus limneticus did not appeared as dominant species in September.3. From April to October in 2013, the influence of different breeding densities on amylase activity and lipase activity in H. molitrix intestinal and TChE activity in H. molitrix brain were investigated in Wenliushui excellent fish breeding grounds in Yongji, Shanxi province, North China. Two experimental groups (each including three ponds) were set, which represent low and high breeding of H. molitrix density of 21.2 g·m-3 and 42.4 g·m-3 respectively. The results showed that amylase activity of high density breeding ponds was higher than that of low density, and amylase activity in foregut is higher than that in hingut, as is the same with the lipase activity. The cell abundance of Cyanophyta in high breeding density ponds was obviously lower, while the proportion of the cell abundance of Chlorophyta was higher than in low breeding density ponds. The amylase activity had a negative correlation with the cell abundance of Cyanophyta but a positive correlation with the cell abundance of the other divisions. The lipase activity had a negative correlation with the cell abundance of Cyanophyta and Euglenophyta, but a positive correlation with the cell abundance of the other divisions. AChE activity in H. molitrix brain of high density breeding ponds was significantly lower than that of low density. AChE activity had a positive correlation with the cell abundance of Cyanophyta and Cryptophyta but a negative correlation with the cell abundance of the other divisions.4. phytoplankton in 6 fishponds was sampled respectively for qualitative and quantitative research and micropore bottom aeration method was applied to three of them. The results show that phytoplankton in fishponds was fallen to 4 divisions,18 families,42 genera and 56 species (include varieties). Among them, Chlorophyta and Bacillariophyta are more than others and were 28 and 16 species respectively, phytoplankton in each fishpond is mainly composed of Chlorophyta, Cyanophyta and Bacillariophyta. With micropore bottom aeration method, the species of Cyanophyta was decreased, meanwhile, the species of Bacillariophyta was increased. The cell density of phytoplankton showed that the proportion of Cyanophyta is thejargest, next is Chlorophyta and Bacillariophyta is the third without micropore bottom aeration method. Whereas, the proportion of Chlorophyta is the largest, next is Bacillariophyta and Cyanophyta is the third. With micropore bottom aeration method, compared with the fishponds without micropore bottom aeration method, the water quality was better in the ponds with micropore bottom aeration method. |
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