Flounder broodstock collection in Ecuador

I worked in Ecuador as JICA (Japan International Cooperation Agency http://www.jica.go.jp/ ) expert in CENAIM (Centro Nacional de Acuicultura e Investigaciones Marinas "Edgar Arellano M." http://www.cenaim.espol.edu.ec/) from 1993 to 1997. The jobs were technical transfer of marine fish seed production, particularly broodstock collection, maturation inducement, seed production and juvenile rearing of snook and flounder.

Fine flounder (Paralichthys woolmani "Lenguado") is one of very popular fish in Ecuador. The fish were fished by gill-net at off-shore where 30 to 50 m depth during winter season, June to September. Water temperature showed 21 to 25C at surface during collection season. The nets, more or less 10 cm mesh and 200 m long, were set in the afternoon and raise in the following morning. We followed the fisherman in the morning and purchased fish which was ideal for brood stock. The conditions for brood stock are the same as robalo. Especially, damage of internal organs were occurred due to net squeezing abdomen. The body weight were 0.5 to 5 Kg, female is bigger than male and the shapes are not different between both sexes.

We bought 132 fish and 19 survived which used for seed production. Based on the dead fish, mature female flounder with the body weight more than 3.2 Kg and GSI (Gonad somatic index, gonad weight /body weight x 100) indicated more than 5 and minimum body weight of mature male was 0.75 Kg which showed sperm when abdomen was pressed.

私は１９９３年から１９９７年にかけて、ＪＩＣＡ（国際協力機構http://www.jica.go.jp/）の専門家としてエクアドルのＣＥＮＡＩＭ（Centro Nacional de Acuicultura e Investigaciones Marinas "Edgar Arellano M." http://www.cenaim.espol.edu.ec/）で働きました。活動内容は海産魚のロバロ（南米スズキ？）とレンガード（ヒラメの近似種）の親魚採集・成熟促進・種苗生産・稚魚飼育の技術協力でした。

エクアドルではレンガード(Paralichthys woolmani、英名Speckled flounder ）は非常に重要な魚種です。レンガードは水深３０から５０ｍに仕掛けられた刺し網で冬季(６～９月）に漁獲されます。漁獲期の海面水温は２１から２５℃でした。網目約１０ｃｍ長さ２００ｍの網は午後に仕掛けられ、翌日の朝に揚げられます。我々は漁師に同行し、漁獲魚より親魚に適した魚を購入しました。親魚の条件はロバロと同じですが、刺し網に掛かっているため内臓の損傷に注意をする必要があります。魚体重は０．５～５Ｋｇでメスはオスより大きく、雌雄の外見上の差異は見られなかった。

最終的に１３２尾の親魚を購入し、内１９尾が生存し種苗生産に使用されました。斃死魚の測定によると、メスは体重３．２Ｋｇ以上でＧＳＩ（生殖腺体指数、生殖腺/魚体重Ｘ１００）が５以上で成熟状態であり、オスは魚体重０．７５Ｋｇ以上で腹部の圧迫により精液が見られた。