Prevalence of skin pseudotumors in starry flounder (Platichthys stellatus) and pleuronectid hybrids in a brackish-water lake, Hokkaido, Japan

北海道オホーツク海沿岸のクッチャロ湖からヌマガレイとオショロガレイ(ヌマガレイとスナガレイの雑種)を採集し,体表の皮膚偽腫瘍の発生状況を調べた。本病変はヌマガレイとオショロガレイともに見られ,カレイ類雑種からは初記録である。ヌマガレイでは,体長10cm 未満の小型魚にのみ病変が認められ,魚体長の増加とともに病変の発生率は減少した。この湖にはカレイ類の魚類捕食者が見られず,また病変の退行や病魚の湖外への移動が考えられないことから,病魚は死亡すると推定した。

Starry flounder (Platichthys stellatus) and Oshoro flounder, hybrids of starry flounder and stone flounder (Kareius bicolaratus), collected in the brackish-water Lake Kuccharo, Hokkaido, were examined for skin pseudotumors. The disease was found in Oshoro flounder, which represents the first record of skin pseudotumors from pleuronectid hybrids. In starry flounder, only small fish (less than 10 cm in body length) had skin pseudotumors, and prevalence of the disease sharply decreased with fish size. No predatory fish was caught in the lake. It thus seems likely that small starry flounder die due to skin pseudotumors in the lake.