| Brachymystax lenok(Pallas), Salmonidae, Brachymystax, is one of the only inland cold-water fishes. In 1988, it was enlisted as a class II protected specie in China. Brachymystax lenok distributes widely in the world and YaLu River is one of the main areas. Recently, its distribution has been shrinking greatly and population has been decreasing, even more, it is on verge of extinction.Among the upriver anabranches of YaLu River, the 13th and 15th streams were chosen as the typical habitats of Brachymystax lenok to investigate its ecological environment. The results indicated:(1)The cold-water area is fit for the cold-water fishes to live, the perennial temperature is below 16℃, pH 6.9~8.3, and the DO is 8.10~15.23 mg/L at the period of non-frozen, which is very suitable for cold-water fish to live in. (2) The organic nourishment is rich, which is important for both the Brachymystax lenok and the hydrophytes to grow. NH4＋-N:0.034～0.378 mg/L,NO2-N:0.00064～0.0.0058 mg/L,NO3-N:0.11～1.15 mg/L.(3) The metals such as K, Ca, Na, Mg can meet the need of algae, and the content so heavy metals is low which didn't result in pollution; Pb,Cd,Hg are all below the threshold quota to be monitored.(4) The peak of plankton appeared at summer, the species of phytoplankton changed according to the seasons, the superiority is diatom,the minimum quantity is 0.325mg／L in Sep.; zooplankton mostly is rotifer,the minimum quantity is 0.625mg／L in July. The phytoplankton quantity is 0.783mg／L and the zooplankton quantity is 3.553 mg／L in July, 2003, which are all more than the quantity resulted in July, 1985.(5) The soil and vegetation along the riversides are all right, most of which can provide shelters for zooplankton. What's more, because of spring flood, some indexes especially NH4+-N was a bit high, maximum is 0.378 mg/L, which might influence Brachymystax lenok's spawning, fecundation and the development of zygote.The domesticated Brachymystax lenok grew a bit more slowly than the wild ones; the survival rate is 30%.after 3 years, and 26% after 6 year. The matured Brachymystax lenok spawned in May and the fry can adapt the water area in cement-pool. The survival rate of Brachymystax lenok that were released in natural rivers could reach 65.1% in 1 year, they could take food and grow normally, and their mature age and condition were almost the same with the wild population. It is found that: some reservoirs on rhe rives, which conditions such as depth, Do, CODMn,BOD5 and nutrients are more benefit to cold-water fishes, plankton is relative plentiful, and their up-stream of entrances are fit for spawning place,They are easy to manage. The achievements of domestication and manual releasing, demonstrated the feasibility to reproduce and put them into rivers under the existing condition. This is very meaningful for the protection of the scarce species. |
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