The dramatic elevation of manganese concentrations in the otolith of Japanese eel Anguilla japonica
Date Issued
2009
Date
2009
Author(s)
Chiang, Chun-I
Abstract
Trace elements in otolith have been widely applied to reconstruct migratory environmental history of the fish and to discriminate the population structure as well. However, the mechanism of deposition of trace elements in the otolith is still not completely understood. The deposition is a complex biogeochemical process was influenced by the environmental factors, the physiology and ontogeny of the fish, as well as the crystal structure of otolith. It is important to understand the mechanism of the deposition of elements in otolith before otolith microchemistry is used for ecological implication. Manganese (Mn) is one of the 31 important trace elements in the fish otolith. The phenomenon of elevated Mn concentration in the otolith core has been found in many fishes, but the factors affecting the concentrations of Mn in otolith are not well understood. The elemental composition in otoliths of 48 wild yellow-stage Japanese eels was examined by laser ablation-inductively coupled plasma mass spectrometry to understand the change of manganese (Mn) concentration in otolith in relation to the life history events of the eel. The otolith microstructure and crystal structure of CaCO3 were also examined by scanning electron microscopy and Raman spectroscopy. In addition, to understand the effects of ambient Mn concentrations on the otolith Mn concentration, the elvers of Japanese eel were reared for 6 months in the laboratory.emporal change of Mn/Ca ratios in the otoliths of wild eels can be classified into 3 types: 1) the Mn/Ca ratios in otolith elevated at early life stage of the eel (81.25 %), the mean Mn/Ca ratios at core region of the otolith in the early stage were significantly greater than those at yellow-stage of the eel (p <0.001-0.05, respectively). 2) Mn/Ca ratios elevated in the yellow eel stage but not in the early stage (8.33%), the mean Mn/Ca ratios at the yellow-stage were significantly greater than that the early stage ( p <0.05). 3) no significant elevation (10.42%). The elevated Mn/Ca ratios in the otolith core region were found in most of the eels examined, suggesting that in the Mn was abundantly uptaken from ambient water at early stage of the eel. The Mn/Ca ratios were not significantly different among 3 types of habitat use of the eel which was classified by Sr/Ca and Ba/Ca ratios in otolith of the eel at yellow stage. In addition, Mn concentration in otolith of reared eels were not significantly different between treatments of KMnO4. This further indicated that the elevated Mn concentration in otolith was not related to the salinity and the ambient Mn concentration. The Raman effect also indicated that the elevated Mn concentration in the otolith was not due to different crystalline structures of CaCO3 because all of the otolith were aragonite, not vaterite. The peak Mn/Ca ratios occurred as Sr/Ca ratios drastically decreased to less than 4 ‰ while arriving at the estuary as elver. The peak Mn/Ca ratios in the otolith of elver stage may reflect its physiological and requirement in the upstream migration. The elevated Mn concentration in the core region of the otolith of Japanese eel was also found in the other temperate eels, A. anguilla and A. rostrata, which seems a common phenomenon of the angullid eel. In conclusion, the elevated Mn concentrations in otolith of the eel at early life stage might be due to the effect of physiology rather than environmental effect or crystalline structure of otolith.
Subjects
Japanese eel
otolith
Mn/Ca ratios
fish physiology and ecology
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