台灣東部海域竹節鰆之生殖生物學研究

Abstract

本研究以台灣東部海域竹節鰆(Acanthocybium solandri)為對象，藉由生殖生物學的研究瞭解該魚種族群動態資訊，提供資源評估所需的生物參數，以確保該魚種資源之永續利用。自2005年12月至2008年12月，在台東縣新港魚市場收集台灣東部沿近海鮪延繩釣和曳繩釣所捕獲之竹節鰆生殖腺樣本並記錄其體長、體重與性別等資料，總計採獲482尾（雌性223尾，雄性259尾）竹節鰆生殖腺樣本，其尾叉長（fork length, FL）範圍為47.5∼148.4公分，體重（round weight, RW）為0.6∼27.0公斤。經卡方檢定月別和體長別性比，結果顯示三年採樣期間，除了2006年8月、2007年6月與2008年6月以及體長105.0~109.9公分該組距以外，各月與各體長別性比均與0.50無顯著差異，三年總性比亦與0.50無顯著差異。依據竹節鰆生殖腺成熟指數（Gonadosomatic index, GSI）與平均卵徑之月別變化，並配合生殖腺組織切片的觀察，判斷台灣東部海域竹節鰆的產卵型式為非同步成熟型（Asynchronous），生殖季節為3月至8月，生殖高峰在4月至7月。估計台灣東部海域竹節鰆雌魚50％性成熟體長為98.9公分，最小性成熟體長為86.3公分；雄魚50％性成熟體長為85.8公分，最小性成熟體長為71.3公分。根據卵巢內排卵後濾泡（postovulatory follicles）退化特徵，估算成熟雌魚的產卵比率為0.17，產卵頻率（spawning frequency）約為6.00天；若以有生殖活動（reproductive activity）之雌魚來推估則約為2.80天，故竹節鰆雌魚於生殖期間接近每三天產卵一次；根據精巢內精子之相對數量和輸精管管壁特徵，估算成熟雄魚的排精比率為0.37，排精頻率約為2.70天，故竹節鰆雄魚於生殖期間接近每三天排精一次。平均單次孕卵數（batch fecundity）為81.3 ± 8.4 (S.E.)萬粒卵，平均相對孕卵數（relative fecundity）為每克雌魚體重含有123.8 ± 9.2 (S.E.)粒卵細胞。推估單次孕卵數（ ）與尾叉長（FL, cm）、體重（RW, kg）及生殖腺重（GW, g）的關係式分別為： 、 及 ，顯示單次孕卵數會隨著體長、體重及生殖腺重增加而增加。

Length and weight data and gonads of 482 (223 female and 259 male) specimens of wahoo (Acanthocybium solandri) caught by the eastern Taiwanese offshore longline and troll fisheries were collected at Shinkang Fish Market from December 2005 to December 2008. Size of the specimens ranged from 47.5 to 148.4 cm FL (fork length) or 0.6 to 27.0 kg RW (round weight). Chi-square tests found a generally homogenous sex ratio of 1:1 among months and 5-cm length intervals, except for the months of August 2006, June 2007 and June 2008, and the length interval of 105.0-109.9 cm. The overall sex ratio was not different from 1:1. Monthly variations in gonadosomatic index, mean diameters of oocytes, and histological examination provided the basis to define the stages of gonadal development. The results showed that spawning season was from Match to August with a peak between April to July. The predicted length at 50％ maturity was 98.9 cm for females and 85.8 cm for males, and smallest size of maturity was 86.3 cm for females and 71.3 cm for males. On the basis of the proportion of females with postovulatory follicles, spawning frequency was estimated at 6.00 days for mature females and 2.80 days for mature and reproductively active females, implying that reproductively active wahoo spawned almost every three days. On the basis of the proportion of males with spermatozoa and the feature of sperm duct, spent frequency was estimated at 2.70 days, implying that reproductively active wahoo spawned almost every three days. The average batch fecundity was 81.3 ± 8.4 (S.E.) ten thousand oocytes, or the average relative fecundity was 123.8 ± 9.2 (S.E.) oocytes per gram of body weight. Relationship between batch fecundity and fork length, round weight, or gonad weirgt was , , and , respectively, indicating that batch fecundity would increase with fork length, round weight and gonad weight.