| Summary: | 碩士 === 國立臺灣大學 === 漁業科學研究所 === 99 === Abstract
Otolith microchemistry has been validated to be a powerful tool in studying the migratory environmental history of fish. The chemical composition in otolith of fish is affected by the ambient water the fish inhabited. The migratory environmental history of the grey mullet, Mugil Cephalus in the Tanshui River was studied by the water chemistry particularly Ba, Sr and Ca, and the elements in the fish otolith. The water samples were collected from 45 sampling stations in the Tanshui River Basin over 5 times from September, 2009 to May, 2011. The data of otolith Sr/Ca ratios of 69 grey mullets and Ba/Ca ratio of 12 grey mullets were obtained from the other studied which was measured by EPMA and LA-ICPMS based on the specimens collected in the same river system from August 2006 to August 2010.
The results are summarized as follows:
(1) The contents of Sr and Ca in water were positively correlated to salinity (R2=0.82~0.95 for Sr and R2=0.93 ~ 98 for Ca. It indicates that Ca and Sr are mainly contributed by sea water and scarcely influenced by artificial contaminant.
(2) The content of Ba in water was negatively correlated to salinity but the correlation is very weak (R2=0.01 ~ 0.07). The Ba content was higher in the middle reaches, the upper limit of the seawater intrusion, and showed unusual high contents in some sampling sites in upper reaches. It reveals that Ba originates from freshwater and might be influenced by artificial contaminant.
(3) The content of Sr in the water significantly increased with increasing salinity, but Ba content decreased with increasing salinity and appeared a peak at tidal mixing areas of the river where turbidity was maximum.
(4) The temporal changes of Sr/Ca ratios and Ba/Ca ratios in otolith provided the opportunity to study migratory environmental history of the mullet in the river.
(5) The grey mullet in larva stage preferred staying in the main river of Tanshui River for the rich foods, than migrated to the three upstream in growth-phase young stage. During maturation, they migrated back to the sea for spawning. The mullet seems to concentrate in the tidal mixing area. This tendency is consistent with the signal of otolith microchemistry of the fish.
In conclusion, Sr/Ca ratios and Ba/Ca ratios in otolith of the mullet in river can reflect complicated dynamics of the water. It is reliable to use the elemental composition in the otolith to reconstruct the migratory environmental history of grey mullet in Tanshui River.
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