- 學位論文
溫度、鹽度與餵食對日本鰻苗(玻璃鰻)體成長，耳石成長與體色素形成之影響
Effect of temperature, salinity, and feeding on somatic growth, otolith growth, and pigmentation of Japanese glass eel Anguilla japonica
摘要
日本鰻苗在變態後遷移的過程中，會遇到許多環境因子像是溫度，鹽度的改變，以及缺少食物的饑餓，都可能間接或直接的影響到魚體本身的成長，體色素形成與耳石的增長。因此本篇實驗將探討溫度,鹽度和餵食對日本鰻苗的體成長、耳石增長以及體色素形成的影響。鰻苗實驗前，先以Alizarin complexone (ALC) 浸泡，再分成4組不同鹽度組 (35、26、17,、0 psu)，各組於餵食或不餵食的條件中進行一個月實驗。為了探討溫度對鰻苗的影響將鰻苗分配到四種不同的溫度 (20、15、10、5 ℃)，並且在不餵食的條件中進行一個月以及兩個月實驗。實驗結果發現，鹽度的改變對於體成長和體色素的形成並沒有太大的影響，不同鹽度組鰻苗體色素階段均較原始對照組達成更成熟期，不過在淡水組VIA4所佔的比例較其他組為高。體長與體重在餵食情況較原始對照組有明顯的增長不過在各鹽度中並沒有明顯的差異，而體色素形成在餵食的情況下在較晚期體色素階段(VIA3 - VIA4)的比例高於無餵食的情況。耳石增長的日平均增加量在無餵食的情況 (0.776 ± 0.094 μm / d) 下少於餵食的情況 (1.070 ± 0.245 μm / d)。而在不同溫度組實驗中，各組平均耳石半徑介於149.83 ± 0.8 μm – 196.21 ± 12.46 μm，隨著溫度的上升而比原始對照組(133.02 ± 9.46 μm) 顯著增加。體色素形成隨著溫度的上升而加速發展到較後期的階段。在經過一或兩個月，在5℃的鰻苗其體色素發展明顯較其它溫度組來的緩慢，並且大部分仍保持在體色素最早期的兩個階段VA - VB。實驗結果發現，溫度與餵食對於耳石增長和體色素形成有較強的影響。鹽度之效應並不明顯。野生鰻苗在低溫與饑餓狀態下，體成長、體色素形成以及耳石生長會顯著停滯，可能因此延後溯河洄游之時間與鰻苗日齡的低估。
並列摘要
Glass eel of Anguilla japonica migrating in the open ocean will encounter with different environmental factors such as temperature, salinity, and starvation, which might affect the glass eel’s status such as somatic growth, otolith growth, and pigmentation stage. This study aims to determine the effect of temperature, salinity, and feeding on somatic growth, otolith growth, and pigmentation of the glass eel. Fish were immersed with alizarin complexone (ALC) then reared at different salinities (35, 26, 17 and 0 psu) under feeding or unfed conditions. To test the effect of temperature, glass eels were reared at 20, 15, 10 and 5 ℃ under unfed conditions. The results of this study indicated salinity appears no strong effect on pigmentation and somatic growth. Because the pigmentation stage at different salinities under feeding or unfed conditions was more advanced compared to the initial group but there was higher percentages in stages VIA4 in fresh waters than in seawaters. TL and W was significantly growth under feeding conditions compared to the initial values but no significant difference was observed in somatic growth among various salinities. And with food supply, there were higher percentages in later stages VIA3 to VIA4 than the unfed groups. The mean otolith growth increment per days of glass eels reared under unfed conditions was significantly lower (0.7757 ± 0.0941 μm/d) than under feeding conditions (1.0703 ± 0.2454 μm/d) of glass eel reared at different temperatures ranges from 149.83 ± .08 μm to 196.21 ±12.46 μm and the mean otolith radius was increased as the temperature elevating compared to the initial value (133.02 ± 9.46 μm) after 1 and 2 months. The pigmentation stage was more advanced into late stage with the temperature was increased, but glass eels reared at 5 ℃, the pigmentation stage developed slowly and remained in early stages VA to VB after 1 or 2 months. According the result of this study, otolith growth and pigment formation of the glass eels were strong affected by temperature and feeding, but these were not affected by salinity. In the wild, when glass eels encounter starvation conditions and low temperature, their somatic growth, otolith growth and pigment formation are significantly slowed down, resulting in delayed the upstream migration time and underestimated the daily age of the glass eels.