| Summary: | 碩士 === 國立臺灣海洋大學 === 環境生物與漁業科學學系 === 106 === The reproductive biology of dolphinfish (Coryphaena hippurus) in the eastern waters of Taiwan was analyzed based on 442 gonad samples collected in Nafanao, Yilan County and Shinkang, Taitung, Taitung County fish markets during January 2016 to April 2017. Body size of the samples ranged from 40.4 to 139.5cm in fork length (FL) and 0.56 to 22.5 kg in round weight. In addition, the sex ratio (proportion of females) was analyzed based on 29,615 (18,407 were females and 10,758 were males) samples measured in Shinkang fish market during 2006 to 2016. The results of Chi-square tests indicated that sex ratio of all samples was 0.63 and was significantly different from 0.5; tests were significant for annually and monthly sex ratios and females more than males, except for 2010, 2012 and August; tests were significant for samples less than 100cm and insignificant for samples larger than 100cm, except for between 110-115 cm and 125-130 cm; all samples were male for samples larger than 140cm.
The results of monthly trends of gonadosomatic index (GSI), mean diameters of oocytes and the gonadal development stages indicated that the GSI, mean diameters of oocytes and proportion of gonad developments belonging to spawning stage during March to July were larger than those in other months, and gonad developments of few samples were assigned to the rest stage. Therefore, dolphinfish in the eastern waters of Taiwan spawned in the entire year with a peak during March to July. Based on the histological examination and the distribution of oocyte diameter, the oocytes of dolphinfish developed asynchronously; the smallest size of mature females and males were 46 and 47.8 cm, respectively; the estimated length-at-50% maturity was 52.3 cm and 55.9 cm for females and males, respectively. The results of postovulatory follicle analysis indicated that the proportion of reproductively active samples was 0.82 during the spawning season and females were estimated to spawn once every 1.25 day; the proportion of mature males was 0.33 and males were estimated to spawn once every 3 days. The batch fecundity estimated to range from 87,000 to 473,960 oocytes and averaged to be 196,446 oocytes using the hydrated oocyte method; the estimated relative fecundity ranged from 7.4 to 66.1 oocytes per gram of body weight and averaged to be 37.5 oocytes.
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