Isolation, Identification And Biological Characteristics Of A Pathogenic Saprolegnia Sp. From Oncorhynchus Masou Masou

Since being introduced and successful artificial breeding in China, Oncorhynchus masou masou has got the favour of people, based on their advantages of tastes fresh, fleshy,smooth, high nutritive value and health function. Thus, it has a broad market prospect in China. In recent years, with the development of technologies, culture and constantly growing, frequent diseases often cause great economic losses, especially of saprolegniasis. Due to its rapid, wide range of infections, mortality of it is high. Therefore, Oncorhynchus masou masou industry was brought into great distress and has a serious impediment to its sustainable development.In this experiment, the traditional method for separation and purification of a strain of pathogenic Saprolegnia strains was used. The morphological and molecular methods were combined to identify the Saprolegnia, and its artificial infection on eggs was assayed. Studies on the biological characteristics, the effects of different growth conditions on the strains, drug prevention and control of water mold growth effect were carried out. A theoretical basis for the biological characteristics of wate mold and prevention of Saprolegniasis was provided. The results are as follows.1. The Saprolegnia strain, named SN, was isolated and purified by traditional method. By observing the fungal which attached to the rapeseed, it was found that the fungal is transparent tube, no diaphragm and has less branching hyphae. At the top of the hyphae was the clavate Sporangia, with the internal zoospore, and the primary zoospore was discharged from sporangium when they were mature. New sporangium generated by internal proliferation or basipetalous succession. Under the centain condition, spherical or irregularly shaped chlamydospores was seen at the top or intermediate of the hyphae. Under the suitable growth condition, the fungal could produce oogonium and antheridium to sexual reproduction. These morphological characteristics were similar with the Saprolegnia.2. The ITS r DNA sequences of strain SN were homology comparison with Saprolegnia sp.from Gen Bank, and it had the closest relationship with the Saprolegia salmonis(Gen Bank accession number: EU551152).Therefore, strain SN was determinated as Saprolegnia salmonis with the GenBank accession number was KJ579137.3. Oncorhynchus masou masou eggs were exposed to different concentrations suspension of the fungal spore to researched the infection rate of strain SN, and it was found that eggs was infected by the spores in water. The spores attached to the eggs, andcould be spread between them. With the increase of spore concentration in water, the infection rate of the Saproleginasis was increased significantly. The infection rate reached 82% when the initial concentration was 1×105 spores/ml.4. Through changing the growth condition to test the biological characteristics of strain SN. We found that the strain SN,s suitable growth temperature in the range of 10 ~30 ℃, and the optimum growth temperature was 25 ℃; the suitable p H range from 5 to 11, the most suitable p H was 8; and the strain SN was sensitive to Na Cl, the strain could grow slowly under the salinity in the range of 0.5 to 2%, but with the increase of salinity, the strains was inhibited significantly.5. Six kinds of Anti-Saprolegnia preparation(Hydrogen peroxide, Formaldehyde, Malachite green, Jian KeⅠ, Peracetic acid and Sodium nitrite) were selected to reaserch the influence of drugs to the growth of the strain SN’s spores. The results showed that the high concentrations has the best inhibitory effect which was multiple of the actual production; and the inhibitiong effect of Formaldehyde and Hydrogen peroxide were better than Malachite Green, since then Jian KeⅠ,Sodium nitrite and Peracetic acid were little effect.6. Kochia scoparia, Cnidium fruit, Cinnamon and other 16 kinds of Chinese herbal medicine and compound T1, compound T2 were selected for testing the inhibition effect of hyphae growth. The result showed that Pomegranate rind and compound T1 can inhibit the growth of strains SN,s hyphae effectively, and Kochia scoparia, Cinnamon, Lemon, Garlic, Sophora flavescens, Polygonatum, Fennel and Calamus almost had no inhibitory effect on strain; Skullcap, Knotweed, Honeysuckle, Chinaberry skin, compound T2, Cnidium, Pseudolaric and Rhubarb were also worded.