Age and growth of the ajime-loach,niwaella delicata, in the yura river, kyoto, japan

The age of the Ajime-loach,Niwaella delicata (a species endemic to Japan), was determined from the number of concentric rings appearing on the cross-sectional surface of the erectile spine (peculiar to Cobitidae). The ages of loaches caught in the Yura River, Kyoto, were determined and growth rates for each sex estimated. It was found that size dimorphism in this species was due to different growth patterns between the sexes, 2.5 years old males being larger than females and usually sexually mature, unlike the latter. Females older than 3.5 years were sexually mature and larger than males of equivalent age.