Relationship between Population Density and Production of the Redspot Masu-Trout Oncorhynchus rhodurus in Japanese Mountain Stream

Abstract

In order to clarify the relationship between population density and production of the age 0 group of the redspot masu-trout Oncorhynchus rhodurus in the upper stream of the river Kumozu, population density, growth and production were monthly examined from 1977 to 1982. The population density and the growths in body length and body weight, markedly fluctuated from year to year. Negative correlation was recognized between growth and population density. The relationship between production and population density could be represented by a dome-shaped curve. The growth and production of the age 0 group was density-dependent in the first four months of life. It was considered that some intraspecific competition originating increase of population density is the most important factor affecting growth and production.