| Summary: | 碩士 === 國立東華大學 === 生物資源與科技研究所 === 98 === Pacific saury, Cololabis saira, is an important commercial fish in the Far East and Taiwan. It is an epipelagically migratory species and widely distributed between the subarctic and the subtropics in the North Pacific. Maturity variations of female Pacific saury among the pre- (May), initial- (June~July), and main- (August~ November) periods of the fishing season were examined with ovary tissue observations related to their age in order to understand the spatiotemporal variations on the maturity of Pacific saury during the spawning migration in the oceanic waters. Five maturity stages of the oocytes in the ovary of female Pacific saury were found in this study, including peri-nucleolus (Pn), early cortical alveoli (CA1), late cortical alveoli (CA2), primary yolk (YF1), and secondary yolk stages (YF2). The highest maturity stage (YF2) was found only in the specimens of the pre-fishing period. The oocyte maturity significantly differed among the tip, middle, and end parts of the ovary. The maturities were highest and lowest in the ovary middle and tip parts, respectively. Most oocyte diameters were smaller than 2 mm when the ovary was developed to the Pn, CA1, and CA2 stages, while the oocyte diameters were about 2~3 and 3~4 mm when the ovary was developed to the YF1 and YF2 stages, respectively. In the pre-fishing period, the saury migratory schools mainly consisted of the CA1 stage individuals followed by the YF1 stage. While in the initial- and main-fishing periods, the saury schools mainly consisted of the CA2 stage individuals followed by the CA1 stage. As to the relationship of the maturity and body length within the fishing season, the body length of the females developed to the CA1 stage in the initial-fishing period was significantly larger than those in the main-fishing period, while the body length of the females developed to the CA2 stage in the initial-fishing period was significantly larger than those in the pre- and main-fishing periods. At body lengths grown to 27~28 cm, most females were developed to the CA2 or higher stages. The gonadosomatic index (GSI) of the females developed to the CA2 stage in the pre-fishing period was significantly larger than that in the main-fishing period. As to age composition, the maturity of the age-one females was generally higher than that of the age-zero females. The maturity of the age-one females developed generally to the CA2 or higher stages, while only few age-zero females had developed to the CA2 and higher stages and were found in the main-fishing period. The oocyte diameters and GSI of the age-one females were significantly larger than those of the age-zero females in the 3 fishing periods. In summary, the maturity of the age-one females was higher than that of the age-zero females in the fishing season, and none of the female saury migrating in the oceanic waters had developed to the condition of instantaneous spawning. Although the highest maturity (YF2 stage) individuals were found in the pre-fishing period, the major maturity level (CA1 stage) of the pre-fishing period was lower than that (CA2 stage) in the initial- and main-fishing periods.
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