Changes in otolith strontium: Calcium ratios in metamorphosing Conger myriaster leptocephali

Content ratios of strontium (Sr) to calcium (Ca) in the otolith of Conger myriaster metamorphosing leptocephali and elvers increased with increasing increment number from the core to the 110th increment and subsequently decreased. The otolith region from the 110th increment to the edge corresponded to the metamorphic stage. The Sr:Ca ratios in otolith edges of metamorphosing leptocephali were inversely related to metamorphic stage, suggesting that the changes in otolith Sr:Ca ratios were influenced by some physiological factor(s) rather than by environmental factors. Sr concentration in leptocephalus somatic tissues was high and decreased as metamorphosis progressed until the late metamorphic stage when the preanal myomere to total myomere ratio was 0.4. Ca concentration was constant throughout ontogenesis. Body Sr:Ca ratios markedly decreased as metamorphosis progressed. Decrease in somatic Sr concentration and the consequent decrease in body Sr:Ca ratios seemed to be associated with the breakdown of glycosaminoglycan (GAG) in gelatinous matrix, which is the major constituent of soft tissue in leptocephali. Catabolism of GAG may also cause a decrease in otolith Sr:Ca ratios during metamorphosis. In leptocephalus otoliths, Sr:Ca ratios may change in association with the synthesis and breakdown of GAGs during ontogeny.