Age and growth of rose bitterling in Shin Tone River.

Abstract

To determine the age and growth of rose bitterling, length frequency analysis and scale and otolith readings were attempted. Of the three methods, the reading of daily otolith growth increments was found to be the most reliable.From two holding experiments it was found that the mean number of increments approximates the number of days between samplings, and this is taken as direct evidence to show that the increments are of a daily nature. From increment reading data, back calculated calendar birth dates were assigned to all the fish sampled, and it was found that their birth dates varied widely ranging from April to October. Age and body-length relationships varied widely among fish of different birth dates. Fish born in spring and summer showed faster initial growth while those born in late summer or autumn showed relatively slower initial growth. Estimated growth from daily growth increments for fish born in June is 39mm SL in one year and 43mm SL in 1.7 years. Observed growth offish born in June and grown in the laboratory was close to the estimated growth of the fish. Most of the individual fish sampled were an age of not more than two years, and it is concluded that the life span for the majority of the individuals would not exceed this by much.