水槽内で飼育したマアジの生殖腺の周年変化
スポンサーリンク
概要
- 論文の詳細を見る
The aim of this study was to establish a suitable experimental system for inducing maturation and spawning of captive reared jack mackerel, Trachurus japonicus. Specifically, we examined annual changes in the gonadal histology of captive jack mackerel. A total of 285 adult fish (147 females and 138 males) were sampled regularly from rearing tanks (3 ton) in the months of May through July (2006). We found that the gonadosomatic index (GSI) values in both sexes increased during May and June. Spermiation was observed in 60 to 80% of males; however, the GSI values were lower for captive males than for wild males of the same stage. In females, vitellogenic ovaries were recorded in only four fish in the annual sampling period. All of the fish sampled were 2 to 4 years old, with fork lengths of at least 200mm. Condition factors (CF) were between 13 and 17. From the above results, we can conclude that in the present experimental set up female jack mackerel fail to proceed into vitellogenesis, even though they are of reproductive age and their size and body condition have developed to mature values. Further studies on the development of reliable techniques for inducing vitellogenesis based on endocrinological dysfunction mechanisms in the gonadal development of captive jack mackerel are necessary.マアジの繁殖情報の精度を向上させるための飼育実験系の確立を目的として,本研究では,飼育下におけるマアジの生殖年周期を調査した.2005年5月～2006年7月の1年3ヶ月にわたり,陸上屋外円形3トン水槽でマアジ親魚を飼育し,定期採集により285尾(雌147尾,雄138尾)を得た.雌雄のGSIは5-6月に上昇した.雄では60-80%の個体で排精が認められたが,GSIは天然魚と比較して著しく低かった.一方,雌では卵黄形成が認められた個体は,4尾のみであった.採取時のマアジ雌雄の年齢は2-4歳で,尾叉長も全て200mm以上あり,CFも13-17であった.以上の結果より,水槽内で周年にわたり飼育したマアジでは,年齢,体サイズ,栄養状態ともに成熟するための条件は整っていたにもかかわらず,卵黄形成は進行しなかった.今後,養成マアジの成熟･産卵誘導実験系を確立するためには,生殖腺の発育不順の内分泌的要因の解明も含め,飼育下で卵黄形成を確実に促進させる技術を開発することが必要となる.
- 2008-10-29