Elevated Otolith Sr:Ca ratios in the African Longfinned Eel from Mangory River, Madagascar

Otolith Sr:Ca ratios have been widely used to reveal the migratory life history of eel species. However, it is still less investigated for African longfinned eel (Anguilla mossambica). Totally 30 individuals in the yellow eel stage are collected from Mangory River, Madagascar and their otolith Sr:Ca ratios are examined by Electron Probe Micro-Analyzer. Temporal profiles in otolith Sr:Ca ratio can be generalized into classical and elevated type. In the classical type (37 %), the Sr:Ca ratios peaked to around 12 to 15 ×10^-3, corresponds to leptocephalus stage in the sea and then decrease after metamorphosis to glass eels, around 2 to 4 ×10^-3 and remained until being caught. In the elevated type (63%), after remaining in a low level for some time, the ratios increased dramatically and exceeded those in the early life stage, ranging from 10 to 30 ×10^-3. Moving to the sea is not sufficient accounting for these elevated Sr:Ca ratios, because the ratios are much higher than in leptocephalus stage when they are in the sea and their bodies contain large amount of glycos-amino-glycans with high Sr affinity. Possible reasons include the experiences in waters with extremely high salinity, or elevated Sr concentration in river waters