Competitive influence of isaza,Chaenogobius isaza,on ayu,Plecoglossus altivelis,in Lake Biwa

1. Competitive influence of the isaza population on the ayu population was studied in Lake Biwa.
2. The results of comparison of ecology of the two species suggest that interaction of ayu and isaza possibly occurs in cold season when there is no other important competitor.
3. The significance of interspecific competition between them is evaluated as a factor controlling the rate of recruitment of juvenile through analysis of the Pre-war catch statistics.
4. Presence of the compensation between the juvenile stage and the adult one relieve the ayu population of influence of interspecific competition which they will suffer in the stage of juvenile.
5. Competitive processes which will be responsible for increase of mortality and reduction of individual growth are discussed.