飯島氏銀鮈（Squalidus iijimae）之生殖生物學研究

Abstract

飯島氏銀鮈（Squalidus iijimae）為臺灣特有種初級淡水魚類，也是被農業部列為瀕臨絕種保育類的重要保育對象。飯島氏銀鮈目前僅於後龍溪流域存在原生族群，且近年於臺中市食水嵙溪雙翠水壩發現一個被引入族群。本種因受到棲地破壞及外來種入侵等影響，數量急遽減少，是亟需採取保育措施的淡水魚種。本研究有二個主要目的，其一為獲取飯島氏銀鮈的生殖生物學資料，包括性別、體長體重關係、肥滿度及生殖腺成熟度指數、孕卵數、卵徑頻度與繁殖季等。其二為建立人工養殖的標準方法，探討最適合飯島氏銀鮈之飼養水溫、水質條件、光照週期、餌料、飼養密度、水體大小等環境因素，並觀察種魚行為表現，確認出最適合飯島氏銀鮈生存的人工飼養環境，以做為未來保育及復育行動的依據，達到降低滅絕風險的結果。本研究以臺中市雙翠水壩的飯島氏銀鮈域外族群為研究樣本，利用釣魚法以每兩週採集15尾的方式，共取得480尾樣本，以解剖方式獲得上述數據，並另採集150尾種魚於人工環境飼養，得到生殖生物學以及人工養殖結果。研究結果顯示，可利用雄魚具第二性徵「追星」做為飯島氏銀鮈性別判斷標準。雄魚之體長體重關係式為W = 0.000006 × L3.2391，R2 = 0.9038，雌魚為W = 0.00002 × L2.9254，R2 = 0.9225。雄魚肥滿度介於0.802–1.035，雌魚則介於0.819–1.144，於8、9月最高，11至2月最低。雄魚生殖腺成熟度介於0.303–3.228，雌魚介於0.303–22.308。總孕卵數介於1,058–6,326顆，且包含發育階段不同之卵粒，為分次成熟型。基於以上生殖生物學資料，推測飯島氏銀鮈之繁殖期為4月至10月，9月為生殖高峰期，且為多次生殖型。飯島氏銀鮈的養殖須提供沒有含氮代謝物之良好水質環境，並謹慎控管魚類常見病原以避免感染。提供赤蟲、豐年蝦及含高蛋白質的人工飼料，待種魚肥滿度明顯增加後，自然配對或利用人工注射激素方式催產。本研究為國內極少數針對瀕臨絕種保育類淡水魚所進行之生殖生物學與人工繁養殖研究之一，不僅填補過去學界對該物種生殖資料的空白，亦為未來飯島氏銀鮈保育策略提供重要科學依據，亦可作為銀鮈屬其他種魚類的研究提供參考。

Squalidus iijimae is an endemic primary freshwater fish of Taiwan and has been listed as an endangered species by the Ministry of Agriculture. Native populations are currently restricted to the Houlong River basin, while an introduced population has recently been discovered in the Shuangcui Dam of the Shishuike Stream in Taichung City. Due to habitat degradation and invasive species, the population has declined sharply, highlighting the urgent need for conservation. This study had two main objectives: (1) to investigate the reproductive biology of S. iijimae, including sex identification, length–weight relationships, condition factor, gonadosomatic index (GSI), fecundity, oocyte size distribution, and spawning season; and (2) to establish optimal artificial rearing conditions, including temperature, water quality, photoperiod, feeding regime, stocking density, and tank size, while monitoring behavior and reproductive performance. A total of 480 individuals were collected biweekly (n = 15) from the introduced population and dissected for data collection. An additional 150 broodstock were used for ex situ culture. Males exhibited nuptial tubercles as a reliable sex indicator. The length–weight equations were W = 0.000006 × L3.2391 (R2 = 0.9038) for males and W = 0.00002 × L2.9254 (R2 = 0.9225) for females. Condition factor peaked in August–September and was lowest from November to February. GSI ranged from 0.303–3.228 in males and 0.303–22.308 in females. Fecundity ranged from 1,058 to 6,326 oocytes, displaying asynchronous development. Spawning likely occurs from April to October, with a peak in September, indicating a multiple-spawning strategy. Artificial culture requires high water quality free from nitrogenous waste and disease control. Fish were fed bloodworms, brine shrimp, and high-protein pellets, with breeding induced by either natural pairing or hormone injection. This study provides the first comprehensive reproductive and captive breeding data for this endangered species, offering essential insights for conservation and serving as a reference for other Squalidus species.