台灣東部鱸鰻苗之來游模式及生長差異

Abstract

鰻魚為東亞重要的經濟魚種之一。目前商業化的人工繁殖尚未成功，鰻苗主要靠野外捕獲。曾出現在台灣的有日本鰻、鱸鰻、太平洋雙色鰻、呂宋鰻和西里伯斯鰻。在台灣養殖漁業，目前以日本鰻最為大宗且養殖技術最為純熟。然而，近幾十年來，由於棲息地喪失及過度捕撈等原因造成日本鰻造成數量遽減，並且被IUCN列為瀕危物種。與日本鰻相比起來，鱸鰻的數量相對豐富。鱸鰻過去曾被列為保育物種，自2009年解禁以來，有望成為日本鰻的替代養殖魚種。鱸鰻為熱帶鰻，與溫帶鰻的日本鰻相比，養殖條件及來游模式亦不同。近年來，開始有多篇鱸鰻養殖條件的研究；然而對於鱸鰻來游模式的研究卻相當有限。如何挑選生長潛能較佳的鰻苗是漁民所關心的，依據養殖戶的說法，清明節前後所取得的魚苗，具有較佳的生長潛能，此說法目前未有相關之研究去證實；此外，關於鱸鰻苗之來游期，前人所調查的結果並不一致。 因此，本研究分析自2011年至2018年於宜蘭河口蒐集每個月份之來游鱸鰻苗樣本，以歸納鱸鰻苗之來游趨勢。另外分別於2018年6月及12月實際捕撈及養殖鱸鰻苗，以比較春季苗及秋季苗之生長差異。研究結果顯示，鱸鰻苗全年都會出現，5月及9月前後有來游高峰，推測這兩波來游高峰是來自不同地理區及產卵時間所造成，經實際養殖後，發現首批來游高峰之春季苗的確有較佳的生長潛能，此結果可作為鰻魚養殖戶挑選鰻苗的參考。

Eel is one of the most economically important fish for aquaculture in East Asia. Owing to the shortage that the yield of artificial eel breeding cannot fulfill the requirement that commercial sale needs, we can only obtain glass eels by catching in the wild. The species of the glass eels that have ever been discovered in the coast of Taiwan are Anguilla japonica, A. marmorata, A. bicolor pacifica, A. luzonensis and A. celebesensis. Recently, the most popular species, A. japonica has been listed as an endangered species by the International Union on the Conservation of Nature due to a number of facts including overfishing and loss of habitat; however, since A. marmorata has been lifted from the conservation list of Taiwan in 2009, A. marmorata can be expected to be the substitute species for eel aquaculture in Taiwan. A. marmorata is a tropical species, compared with the A. japonica, the cultured conditions and the recruitments pattern are different. In recent years, there have been many studies on aquaculture techniques of A. marmorata. However, research about the A. marmorata recruitment pattern is quite limited. How to select the elvers with better growth potential have been issues that people engaging in aquaculture concern. According to fishermen saying, elvers recruited around the Tomb Sweeping Day, seems to have better growth performance. However, such a statement has not been confirmed by scientific methods. Besides, the dominant recruitment seasons of the glass eels of A. marmorata in Taiwan is not consistent as indicated by previous studies. Therefore, this study collected the A. marmorata glass eels in Yilan River of eastern Taiwan from 2011 to 2018 to investigate the detailed recruitment patterns. Besides, sampled the glass eels in June and December 2018 and cultured for twelve weeks respectively for comparing the growth performance of glass eels from different seasons. Results showed that the A. marmorata glass eels recruits to eastern Taiwan throughout the year and reach peaks roughly in May and September. The two recruitments may come from different geographic regions with different spawning time. We sample and culture the glass eels around these two peaks and found that the spring recruitments grow faster than those of autumn recruitments. The results could be used as an index to select elvers for aquaculture.