- 學位論文
鹽度與餌料對日本鰻鰻線體成長及耳石鍶鈣比的影響
Interactive effects of salinity and diet on growth rate and strontium:calcium ratios in otolith of Anguilla japonica
摘要
鰻魚為降海洄游型魚類，一生當中會在淡水與海水之間洄游，近年來有相當多的研究利用其耳石鍶鈣比來回推鰻魚洄游環境的歷史，因此，本研究期由實驗室的控制實驗，驗證鹽度與餌料對魚體組織鍶鈣比、耳石鍶鈣比及分配係數的影響。 實驗設計是先以四種不同濃度（15、25、50及75ppm）的茜素水溶液以及三種浸泡時間（6、12及24小時）進行耳石的螢光標示試驗，結果發現所有組別的鰻線耳石都能產生清楚的螢光記號。 接著將鰻線在五種鹽度（0、5、15、25、35psu）以及三種餌料（鰻粉、紅蟲、飢餓）狀況下飼養30天。結果發現飼育水中鈣與鍶的濃度均隨著鹽度自0 psu至35 psu呈線性增加，鍶鈣比則由0 psu淡水的7.91±0.41´10-3增加約2倍至5 psu海水的15.07±0.63´10-3，而5-35 psu海水中則沒有顯著性差異。餌料部分，紅蟲鍶鈣比約為鰻粉鍶鈣比的四倍。耳石鍶鈣比在經由電子微探儀分析後則發現其在不同餌料之間並沒有顯著性差異，但會隨著鹽度的上升而增加，耳石鍶鈣比跟飼育水中鍶和鈣濃度與鹽度的關係較相似，直線迴歸關係式為[(Sr/Ca)×1000]otolith= 0.091S+ 3.790, n=787, r=0.71, p<0.001，進一步以二次迴歸曲線來擬合則出現更高的相關性（r= 0.76），微分後，求得此二次曲線中鍶鈣比隨鹽度變化的最大值在鹽度29.37 psu。即耳石鍶鈣比會隨著鹽度的增加而升高，但是到達鹽度29.37 psu後，則不升反降。由本研究結果發現，耳石的元素累積在較高的鹽度下可能受到抑制，而非一般認為的直線關係。因此，將來以耳石鍶鈣比應用在區分鰻魚在較高鹽度的生活履歷研究，需要格外小心。 另外也發現鍶鈣比在（a）飼育水與魚體組織、（b）飼育水與耳石、（c）餌料與魚體組織、（d）餌料與耳石、（e）魚體與耳石之間的分配係數都有顯著性的直線迴歸關係式；由以上的結果說明鍶鈣比在不同屏障之間的分配係數，直接受到鹽度的影響，而分配係數會隨著鹽度的升高而增加，鹽度愈高，受到的影響愈大，累積的量愈多，依此結論，對應到野生的鰻魚，能夠回推生活史中的棲息環境，提供更精確的訊息。
並列摘要
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.