Spawning activities of the fluvial Japanese charr Salvelinus leucomaenis and incubation of their eggs at the artificial spawning sites

摘要

Spawning activities of the fluvial Japanese charr Salvelinus leucomaenis and incubation of their eggs were studied at the artificial and natural spawning sites in a small tributary of the Kinu River, central Japan, from October 1996 to March 1997. According to the conditions of natural spawning sites, Two artificial spawning sites which were about 2 m wide and 6 m long and 2 m wide and 9 m long were constructed from logs, boulders, and gravel at the upper and lower reaches of the tributary in mid October. Spawning behaviors of the charr were observed at both artificial and natural sites by mid November. A total of 51 egg pockets with 8101 eggs and 12 pockets with 2119 eggs were observed at the artificial and natural sites in early January, respectively. The ratio of eyed eggs was 78.0+-19.5 percent (mean+-S.D.) at the artificial sites being significantly higher than that of the natural sites (60.1+-30.3 percent). Alevins were observed in both artificial and natural sites in mid March. Construction of artificial spawning sites may be effective in the conservation and enhancement of the Japanese charr.