Gero Branch, Gifu Prefectural Research Institute for Freshwater Fish and Aquatic Environments, Gero, Gifu 509-2592, Japan
We released mature male and female amago salmon Oncorhynchus masou ishikawae reared in a hatchery into a small stream in central Japan and surveyed the location of spawning sites, water depth, current velocity, substrate size and the egg eyeing rates in the redds in 2007.
The redds were observed only at the pool ends and in riffles. The average water depth was 20.5±9.0 cm (Mean±SD). Averages of surface and bottom velocity were 22.7±9.1 cm/sec and 16.1±10.7 cm/sec, respectively. Preferred substrate size was fine pebbles of 16-32 mm. The average egg eyeing rate in the redds was calculated to be 90.6%. As a result, physical characteristics of redds and egg eyeing rates observed in our study were similar to the values of wild fish reported in previous studies.