利用耳石探討台灣東部海域竹節鰆的年齡與成長

Abstract

本研究利用耳石的橫斷切面作為年齡查定的形質，探討台灣東部海域竹節鰆之年齡與成長。自2006年1月至2008年12月間，在台東成功新港魚市場總共採集到436尾竹節鰆樣本，其體長(尾叉長FL)範圍介在47.5~138.7公分之間，體重(全重RW)範圍在0.6~21.5公斤之間。分析量測資料，得知竹節鰆的體長體重關係為RW=6.653×〖10〗^(-7)×〖FL〗^3.475。 研究結果顯示尾叉長在116公分以下的竹節鰆，可以判讀日週輪來鑑定其日齡；尾叉長在116公分以上，則因為靠近耳石邊緣其日輪難以判讀，需使用年輪來判定其年齡。尾叉長在116公分以下的竹節鰆樣本，判讀的日齡介在87~399天。以平均百分誤差(APE)及變異系數(CV)來評估其精確度，重覆判讀3次的結果，其APE值之平均為0.96%；CV值之平均為1.27%。而判讀的最大年輪為3輪，經校正後為3.7歲。以150天為分界，將所有判讀結果分別套適Gompertz 及von Bertlanffy方程式，估得成長參數分別為：L∞ = 74.47 cm，G = 15.126 yr-1，t0 = 0.182 yr以及L∞= 132.35 cm，K= 2.067 yr-1，t0 = 0.058 yr。日齡判讀結果顯示，絕對成長率(AGR, absolute growth rate)隨著日齡的增加而下降，前4個月的平均成長率為5.69 mm/day，顯示竹節鰆在幼齡時期成長快速。回推孵化日主要介在3到8月間，涵蓋台灣東部海域竹節鰆的產卵季節。 年輪的判讀在第一輪較不易驗證，因此本研究主要使用日齡來探討竹節鰆幼齡魚之成長，並確認切片耳石是竹節鰆日齡的最佳判讀工具，本研究補正前人研究高估竹節鰆幼魚成長的缺失，竹節鰆在1歲以下成長快速，且雌雄間成長速率並沒有顯著差異。

Age and growth of wahoo, Acanthocybium solandri, in the waters off eastern Taiwan were studied using the transverse sections of sagittal otoliths. A total of 436 fish ranging from 47.5 to 138.7 cm FL (fork length) and from 0.6 to 21.5 kg RW (round weight) were collected at Shinkang fish market during January 2006 to December 2008. The relationship between the round weights and fork lengths was RW=6.653×〖10〗^(-7)×〖FL〗^3.4745. Results indicated that daily increments could be read for fish smaller than 116 cm FL, while annual counts could be read for fish larger than 116 cm FL. The number of daily increments ranged from 87 to 399 days for the samples <116 cm FL. The ageing precision was 0.96% in terms of average percent error (APE) and 1.27% in terms of coefficient of variation (CV). The biggest annual counts for the sample fish >116 cm FL was 3 annuli which was adjusted to 3.7 years. All data were separated at 150 days into two groups for fitting two growth curves. The fitted Gompertz growth function for the smaller fish was L_t=74.47×e^((-e^(-15.126(t-0.182) ) ) ), and the fitted von Bertalanffy growth function for the larger was L_t=132.35×(1-e^(-2.067(t-0.058) )). Absolute growth rate (AGR) decreased with increasing age, and the average growth rate among the first four months was 5.69 mm/day indicating that wahoo grow very fast in their early life history. Back-calculated hatching dates span from March through August covering the whole spawning season of wahoo in the waters off eastern Taiwan. We acknowledge that identifying first annulus was much difficult. Thus in this study, we used daily increments to investigate the growth of wahoo at young age and proved that the transverse sections of otoliths were the best medium to age wahoo. This study makes up for the overestimation on the growth of young wahoo by previous researchers. Wahoo have rapid growth at their first year of life, and the growth rates do not differ between sexes.