イワナ・ヤマメ養殖魚の小型魚と大型魚の釣獲放流後の死亡率と成長を実験池において調査した。餌釣り,毛鈎釣りともに,口腔にかかった鈎を除去した場合,いずれの魚種においても死亡率は低かった。餌釣りで口腔より奥にかかった鈎を除去した場合,イワナ小型魚とヤマメ大型魚では死亡率は高かった。口腔にかかった毛鈎を残留させた場合,イワナ大型魚では死亡率は高かった。死亡のほとんどが釣獲放流後14日以内に観察された。釣獲方法,鈎がかりの部位,鈎の処理方法は成長と肥満度に影響しなかった。Mortality and growth of Japanese charr Salvelinus leucomaenis and masu salmon Oncorhynchus masou masou after catch and release were examined in experimental ponds, using hatchery-reared fish divided into smaller (< 15 cm in total length) and larger (> 15 cm) size groups. When the hooks stuck in the mouth and were removed for both species, the mortality within 21 days after catch and release was low (O-15.0%) for each size and fishing gear (bait and fly-fishing, using barbed hooks). When hooks in bait fishing were removed from the esophagus, mortalities were relatively high (66.7% in the smaller sized charr and 45.0% in the larger sized salmon). All the fish of both species and both size groups were alive when the hooks in fly-fishing were removed from the mouth, however the mortality was relatively high (40.0%) when the hooks were not removed from the mouth of the larger sized charr. 0f all the fish that died, 63.0 and 98.1% died within 3 and 14 days after catch and release, respectively. There was no negative effect of the catch and release on the growth and condition factor of both species and both size groups. These results suggest that catch and release is effective for conserving Japanese charr and masu salmon populations in rivers and lakes when anglers pay attention to the removal of hooks.