Short-term Effects Of Three Commonly Used Fish Drugs On Water Quality And Community Structure Of Plankton In Freshwater Pond

With the development of freshwater aquaculture and people’s increasing demand for fresh water aquaculture products, nowadays, fresh water pond breeding density is becoming bigger than before, many diseases are broke out at this time. Various types of fishery drugs had also been applied to the pond to treat disease or improve the breeding environment of water, but after applying them, the pond water environment and the phytoplankton community structure also changed, it remains to be studied. In order to regulate the use of fishery drugs, reduce drug residue, improve the quality of aquatic products, this topic is studying the pond water quality and plankton community structure of major change when used fishery drugs(abamectin, trichlorfon and chlorine dioxide represented).The main research results are as follows:(1) After application of commonly dose the abamectin(0.0375ml/m3), the pond water quality and plankton community had changed. The nitrate level was decreased significantly, whereas nitrate nitrogen, ammonium nitrogen and total nitrogen were increased significantly. There were no significant differences in phosphorus, soluble phosphate and p H. The dominant species of phytoplankton and zooplankton changed significantly after the application of abamectin, and miniaturization species increased. The density and biomass of protozoa and cladocera decreased significantly, the number of copepods increased significantly, whereas the density and biomass of rotifers did not change much. The microscopic examination showed 6 phyla with 80 species of phytoplankton, 32 genera with 41 species of zooplankton before the application of abamectin, 7 phyla with 94 species of phytoplankton, 38 genera with 48 species of zooplankton after the application of abamectin. Among them, 10 kinds of protozoa, 5 kinds of rotifers, 9 kinds of Chlorophyta, 1 kind of Bacillariophyta and 2 kinds of Euglenophyta were only found before the application of abamectin; 9 kinds of protozoa, 10 kinds of rotifers, 3 kinds of copepods adult, 10 kinds of C hlorophyta, 8 kind of Bacillariophyta, 7 kinds of Euglenophyta, 1 kind of Pyrrophyta and 1 kind of Chrysophyte were only found after the application of abamectin. The use of abamectin also led to the changes of the structure of plankton. The use of abamectin pond prone to naked algae blooms.(2) Using the commonly dosage(0.0375g/m3) of chlorine dioxide in gong ’an chonghu fishery, the results showed that chlorine dioxide could lead a significant reduction of dissolved oxygen and a slight reduction of nitrate nitrogen, ammonium nitrogen and total nitrogen, nitrite nitrogen, phosphorus and total phosphorus, a rise of p H. Plankton species had changed after the medicine, biomass were significantly decreased, led to the change of the dominant species, miniaturization of algae. The species of phytoplankton increased from 6 phyla 44 genera and 79 species to 7 phyla 52 genera and 109 species and zooplankton increased from 36 genera 43 species to 44 genera 69 specie after using the chlorine dioxide. The community structure changed greatly, some genera and species disappeared and some appeared, such as Chlorophyta( 6 species, 2 genera disappeared; 12 species, 4 genera appeared), Bacillariophyta(2 species, 1 genus disappeared; 7 species, 5 genera appeared), Euglenophyta(2 species disappeared; 15 species, 1 genera appeared), Cyanophyta(2 species, 1 genus disappeared; 7 species, 5 genera appeared), Pyrrophyta(2species, 2 genera appeared). Dinobryon divergens was found in the experiment. After the use of chlorine dioxide, we found protozoa 29 genera 42 species(7species, 6genera disappeared; 24 species, 16 genera appeared), rotifera 15 genera 17species(3species disappeared; 8species appeared) and the dominant species didn’t change, cladoceran species didn’t change and copepods changed(4 species, 4 genera appeared).(3) After application of commonly dose of the trichlorfon(0.283 mg/L), we found a significant reduction of dissolved oxygen, a slight reduction of p H, nitrate nitrogen, ammonium nitrogen and total phosphorus and a increase of total nitrogen in the pond water. There was no significant effects of the soluble phosphate and the nitrate nitrogen. There were 65 specie 44 genera 7 phyla belong to phytoplankton and 31 specie 27 genera belong to zooplankton before using trichlorfon. However, it was found 80 specie 52 genera 6 phyla belong to phytoplankton and 50 specie 34 genera belong to zooplankton after using trichlorfon. The species of C hlorophyta, Bacillariophyta and Euglenophyta changed significantly, such as C hlorophyta(4 species, 1genera disappeared; 9 species, 4 genera appeared), Bacillariophyta(2 species, 1 genus disappeared; 10 species, 6 genera appeared), Euglenophyta(3 species, 1 genus disappeared; 4 species, 1 genera appeared). Dinobryon divergens was found in the experiment. After the use of trichlorfon, we found Protozoa 3 species, 2 genera die out; 6 species, 4 genera occurance and Rotifera 1 species die out; 1 species occurance. A few points also found Cladocera(Alona affinis and Chydorus ovalis and Diaphanosoma leuchtenbergianum) after test. Copepods disappeared 2 adults, 1 adult appeared. It slightly increased the density and significantly increased the biomass of phytoplankton after the application of trichlorfon, which mainly caused by the change of the Euglenophyta and Cryptophyta. Phytoplankton species increased, due to the increase of Euglenophyta and Cryptophyta. Water quality became badly. The use of trichlorfon inhibited the growth of copepods, reduced the predation pressure of small zooplankton, increased small zooplankton. Which cause the deterioration of the appetite of fish.In summary, in considering the fish main growth period(6-10 months) use fishery drugs will reduce the quality of the pond water quality. The specific performance are as following: the dissolved oxygen will reduces; ammonium nitrogen and nitrate nitrogen increase will lead to poison material hurts aquatic organisms, such as; sometimes already become naked algae hyd ration; the natural bait fish, zooplankton will reduce adverse factors. Therefore, it is harmful to use this kind of fishery drugs in aquaculture ponds.