Thornfish(Terapon jarbua Forsskal)is one of the dominant species of fish in thecoastal waters and estuaries of Taiwan.Its larvae and juveniles migrate to these areasduring April to October.This study compared the difference in the morphology of otolithbetween the normal and deformed thornfish collected in the waters around the thermaleffluent outfall of the Kin-Shan nuclear power plant and in the estuary of Gong-Shy-Tyan Creek in northern Taiwan.Also,the daily ages and early growth life history ofthe deformed thornfish were examined.Fish length and otolith length relationship wassignificantly different between the normal and the deformed,but not for the length-weight relationship.The thornfish migrated to the nearshore waters at the age of approximately21 days after hatching.The deformity was due to high temperature.Growthof otolith was faster in the deformed than the normal.This leads to uncoupling of somaticand otolith growths for the deformed fish.