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日本鰻在淡水池養殖3年後，第4年分別養在淡水或鹹水池中。第4年之養殖期間，按月逢機取樣6尾。計採144尾標本魚中，性別比例雌鰻為75.00%，雄鰻22.22%，未能分辨性別者佔2.78%。全長 70～79 cm 或體重大於(含) 800 g時，雌鰻之出現率最高；全長50～59 cm或體重介於300～399 g時，雄鰻之出現率最高。 雌鰻在鹹水養殖環境中，其肥滿度與水溫呈正相關 (p<0.05)，但在淡水養殖環境中則兩者呈不相關 (p>0.05)。不論是在淡水或鹹水養殖環境，雌鰻之生殖腺成熟指數 (GSI) 與水溫均成負相關 (淡水組: r=-0.88, p<0.05; 鹹水組: r=-0.59, p<0.05)。12月份低水溫期，鹹水養殖雌鰻GSI之平均值最高，其值為 1.65±0.60；而在高水溫期之8月，平均GSI值最低，僅為0.72±0.10。 自10及11月份起，各取鹹水組之雌鰻40尾，在相似之條件下，以同劑量之催熟激素誘導雌鰻成熟結果發現，可使其體重增至初體重之120% 以上且達成熟體型。自11月份開始催熟之雌鰻所需之催熟次數比自10月份開始者少，顯示池中養殖之鰻魚在11月份時，其生殖腺比10月份有更進一步之發育。

Japanese eels Anguilla japonica, after cultured in fresh-water ponds forthree years, were stocked in fresh-water or salt-water ponds for one more year.During the last year, eels were sampled monthly from each pond to check and
analyze their maturity value. The sex percentages of eels were 75.00% of females and 22.22% of males(3.38:1), 2.78% couldn't be differentiated. Eels with body length of 70 to 79 cmor body weight of more than 800 g were mostly female. Those with body length of50 to 59 cm or body weight of 300 to 399 g were mostly male.
The condition factor of female eels stocked in salt-water pond was withpositive correlation to water temperature (p<0.05), while those stocked infresh-water ponds showed no correlation (p>0.05). The GSI of female eels,whether stocked in fresh-water or salt-water pond, was with negative correlationto water temperature (p<0.05).
In December, female eels stocked in salt-water pond with low watertemperature had the highest average value of GSI (1.65±0.60). The average GSIwas lowest (0.70±0.10) in August with high temperature.
Female eels stocked in salt-water pond were sampled (40 for each group) andinjected with the same quantity of hormones from October or November,respectively, to induce maturity. The results showed that body weight of bothgroups could increase to 120% initial weight. Yet injection times needed forfemale eels induced from November was less than that from October, demonstratedthat gonads of female eels in November developed further than in October.