- 學位論文
以穩定性同位素分析解析七星鱸魚之棲地利用與辨識養殖和野生個體
Application of isotopic analysis to reconstruct habitat use of Japanese sea bass (Lateolabrax japonicas) and discrimination from reared fish
摘要
日本花鱸，又名七星鱸魚，主要分布在中國東海、日本海和台灣海峽一帶，屬廣溫、廣鹽物種。在台灣區域的主要產卵季於冬季，鱸魚在河口產卵後，可能會進入淡水河流中覓食，但是目前對於此魚種的河海遷徙生活史與行為所知有限。此外，各種魚苗放流在台灣實施多年，卻甚少評估效益，主要原因之一是缺乏能夠鑑別養殖放流個體與野生個體的方法與技術。因此本研究藉由分析野生和養殖七星鱸魚的耳石及組織中的穩定性同位素及耳石鍶鈣比，探討台灣周遭海域七星鱸魚的洄游生活史，並辨別鱸魚個體之來源。受到環境食性差異不同影響，養殖樣本不論是肌肉或耳石中的碳同位素值（δ13Cmus: -19.8 ± 0.2 ‰, δ13Coto: -9.1 ± 0.6 ‰）變異和數值均顯著較野生樣本（δ13Cmus: -16.9 ± 1.5 ‰, δ13Coto: -4.9 ± 1.8 ‰）低，為辨別野生和養殖個體來源的關鍵因子。而根據鹽度換算公式（δ18Ow (VSMOW) = 0.18 S – 6.11）所推估出的鹽度範圍約落於0-39 ppt，橫跨了淡水和海水環境。配合耳石年輪推估時序所得的個體生活史鹽度變化可得知：鱸魚於冬季出生後會直接進入淡水和半淡鹹水河口覓食，而部分個體會持續滯留於較高鹽的海域。相同族群間的個體並沒有一個固定的洄游模式。鍶鈣比分析部分，養殖（3.7 ± 0.2 (10-3)）和野生樣本（4.7 ± 1.5 (10-3)）之間具有顯著差異（K-W test, p = 0.007）。然而，利用耳石氧同位素所估計之鹽度變化和耳石中的鍶鈣比變化並不完全一致。相較於鍶鈣比和耳石氧同位素，估計鹽度時序圖能更完整地呈現個體在不同生活史階段中，於淡水、半淡鹹水和海水棲地之間的變化，有效建立該魚種的河海洄游生活史，並提供將來相關漁業管理單位對於放流魚苗的策略規劃和個體辨識之參考。
並列摘要
Japanese sea bass (Lateolabrax japonicas) widely distributed from Japan to the South China Sea may show diadromous migration. However, the migratory behaviors of this species are rarely studied and still unclear. Japanese sea bass is a food fish providing from fish farming or fishery catch. Stable isotopic analysis of otoliths and muscles were conducted to clarify the habitat use of wild Japanese sea bass and to discriminate the wild population from cultured fish. Otolith δ18O values and water temperature during the corresponding period were used to predict the salinity experienced by the fish. The estimated salinity profiles suggested some Japanese sea bassentered the estuaries and rivers to forage during different life stage. However, some fish completely resided in the marine environment. The stable isotopic composition were more variable in wildfish (δ18O: -3.0 ± 1.3 ‰; δ13C: -4.9 ± 1.8 ‰, n = 18) than in the reared fish (δ18O: -4.1 ± 0.3 ‰; δ13C: -9.1 ± 0.6 ‰, n = 7). In addition,the stable isotope composition of otolith (K-W test, δ18Ooto: p = 0.025; δ13Coto: p = 0.001) and muscle(K-W test, δ15Nmus: p = 0.036; δ13Cmus: p < 0.001) were significantly different between the hatchery and wild fish.These results suggested that Japanese sea bass can use diverse habitats from rivers, estuaries to oceans. The stable isotopic compositions of otoliths and muscles are useful tools to distinguish between wild and aquaculture fish.