| Summary: | 碩士 === 國立臺灣大學 === 海洋研究所 === 97 === 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.
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