| Summary: | 碩士 === 國立臺灣大學 === 動物學研究所 === 92 === Japanese eel, Anguilla japonica, is a catadromous fish, that spawned in the sea and migrating between sea- and freshwater. Otolith strontium (Sr) / calcium (Ca) ratio has been widely used for recording the migratory history of fish, but the interactive relationship between otolith Sr /Ca ratio and environment factors remained unclear. The goal of this study is to understand the effects of salinity and feeds on the otolith Sr/Ca ratio and their distribution coefficients of A. japonica. Elvers (average size at 54.7 ± 2.1mm) were immersed in 50 ppm alizarin complexone (ALC) solution for 6 hours to produce fluorescent marks for identifying the onset of the experiment. They were then reared in different condition with 5 different salinities (15, 25, 50 and 75 psu) and 3 types of feeding conditions (formulated feed, turbifex and starvation) for 30 days. Sr and Ca concentrations in water, feeds and otolith were analysed with AA and EPMA, respectively. The results showed that the concentration of Ca and Sr in water increased with salinity (SAL) ([Ca]water = 15.50SAL — 5.56, [Sr]water = 0.21SAL + 0.03). Although Sr/Ca ratio of tubifex is 4 times higher than that of formulated feed, the otolith Sr/Ca ratio were the same among the different feeding groups (p > 0.05), despite the somatic growth rates were significantly different among the groups (p < 0.01). The Sr/Ca ratio in otolith increased significantly with salinity ([(Sr/Ca) ´ 1000]otolith = 0.091SAL+3.790). Distribution coefficients between ambient water and fish tissue、ambient water and otolith、diet and fish tissue、diet and otolith、fish tissue and otolith were all increase with the increase of salinity. The results suggest that the positive relationship between otolith Sr/Ca ratio and salinity would not be interfered by feeds and somatic growth rate; therefore, it is reliable to study eels’ migration history by using otolith Sr/Ca ratios.
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