臺灣東部海域鬼頭刀的日齡與成長之研究

Abstract

本研究利用耳石作為年齡查定之形質，以瞭解台灣東部海域鬼頭刀之日齡與成長關係，並使用掃描式電子顯微鏡對三顆耳石之外部形態作觀察與描述。自2004年2月至7月及2005年1、2月在台東成功漁港共採集215尾鬼頭刀樣本，體長範圍為24公分至74.4 公分尾叉長，體重範圍為115公克至4200公克，因鬼頭刀耳石在實驗過程中易碎或研磨失敗，最後可供計數之樣本數為58個，體長範圍為28.3至74.4公分尾叉長。 同時有體長體重資料的鬼頭刀共202尾，以變積分析雌雄間體長體重關係式經檢定無顯著差異，得出尾叉長（FL）與體重（W）關係式為W=7.0×10-6FL3.09。比較光學顯微鏡與電子顯微鏡下計數之日輪數並無差異，故採用光學顯微鏡400倍與1000倍判讀耳石上之日週輪，來估算鬼頭刀日齡與成長之關係，鬼頭刀樣本體長在28.3 cm FL至74.4 cm FL內所估算的日齡範圍為79~226天，以平均誤差百分比（APE）評估日齡判讀之精確度，重複兩次判讀之平均誤差百分比平均為1.6%。將尾叉長與估算之日齡，以直線迴歸式套適得出，雄魚成長方程式為FL=0.42D-11.07，雌魚成長方程式為FL=0.39D+4.26，推得鬼頭刀之雄魚平均月成長率為12.5公分尾叉長，雌魚平均月成長率為8.9公分尾叉長，雄魚成長率顯著高於雌魚；本研究樣本內鬼頭刀成長率低於加勒比海及夏威夷，雄魚高於地中海，雌魚則與地中海鬼頭刀成長率相近。由鬼頭刀估算日齡與捕獲日期逆推算產卵期，並參考過去文獻，推論台灣鬼頭刀全年均有產卵活動。

The age and growth of the dolphinfish, Coryphaena hippurus, in waters off eastern Taiwan was studied from the counts of growth increments on the otoliths. Specimens of otoliths were collected from a total of 215 dolphinfish ranging from 24 to 74.4 cm fork length (or 115 to 4,200 grams in body weight) landed at the ShinKang Fish Market of Taitung (eastern Taiwan) during the periods from February to July 2004 and from January to February 2005. Of which, 58 specimens ranging from 28.3 to 74.4 fork length were aged successfully. The average percent error of the ring reading was 1.6%. There was no significant difference in length-weight relationship between the female and male dolphinfish. An equation of W=7.0×10-6FL3.09 was obtained from the sex-combined length-weight data of 202 dolphinfish. Linear relationships between fork lengths and the daily growth increments were used to estimate the growth rates for the dolphinfish in the size ranges of this study. Significant difference in growth rate was found between female and male dolphinfish, and the males grew faster than the females. The growth rates were 12.5 and 8.9 cm fork length per month, respectively, for the males and the females, which were lower compared to those in Caribbean Sea and Hawaii, but higher than those in Mediterranean Sea. The distribution of back-calculated dates supports that the spawning of dolphinfish takes place year around in waters off eastern Taiwan.