報告書番号

U92025

タイトル（和文）

酸性水に対するコイ，アユおよびイワナの稚魚の忌避行動

タイトル（英文）

AVOIDANCE REACTIONS TO ACID WATER BY CARP,AYU AND JAPANESE CHAR

概要 （図表や脚注は「報告書全文」に掲載しております）

コイ，アユおよびイワナの稚魚の行動に及ぼす酸性ｐＨの影響について検討を行った。実験はＹ字型水槽の水路の一方にｐＨ無調整の地下水（対照水，ｐＨ＝７．５～８．１）を，他方に，強酸（硫酸，硝酸または塩酸）を添加し低ｐＨに調整した地下水（酸性水）を注水して，酸性水に対する魚の行動を観察した。各魚種とも１回の実験には６～１１尾の稚魚を供試した。観察は人の動きの影響を除くためＴＶカメラを用いて行った。酸性水に遭遇すると，コイの場合は対照水のｐＨ値よりも概ね１．５以上低下したとき，またアユとイワナでは概ねｐＨ１．８以上の差ができたときに対照水側に忌避行動を取ることが明らかとなった。なお，これら各魚種が忌避行動を示したｐＨ値は，コイで５．３～６．６，アユで５．５～６．４，イワナで５．６～６．４の範囲であった。

概要 （英文）

AVOIDANCE REACTIONS TO ACID WATER BY JUVENILES OF THREE SPECIES OF FRESHWATER FISH WERE INVESTIGATED USING A Y-MAZEWHICH ALLOWED FISH TO CHOOSE CONTROL OR ACIDIFIED WATER. THE CONTROL WATER WAS WELL WATER (PH 7.5 8.1). THE PH OF THE TEST WATER WAS ADJUSTEDUSING SULFURIC ACID,NITRIC ACID,OR HYDROCHLORIC ACID. THE REACTIONS OFTHE TESTED FISH WERE OBSERVED USING CLOSE-CIRCUIT TV TO ENSURE THAT THE FISH BEHAVIOR WAS NOT AFFECTED BY OBSERVER MOVEMENT AND OTHER EXTRANEOUS FACTORS. SIX TO 11 JUVENILE FISH WERE USED FOR EACH EXPERIMENT. THEPH LEVEL IN THE TEST ARM OF THE APPARATUS WHEN ALL THE FISH IN AN EXPERIMENTAL GROUP MOVED TO THE CONTROL ARM WAS CONSIDERED TO BE THE AVOIDANCE PH. THE RESULTS ARE AS FOLLOWS: (1)NO DIFFERENCES WERE OBSERVED BETWEEN THE THREE TESTED ACIDS. (2)CARP MOVED TO THE CONTROL ARM OF THE APPARATUS WHEN THE PH IN THE TEST ARM WAS 1.5 LESS THAN IN THE CONTROL ARM. (3)AYU AND THE JAPANESE CHAR MOVED TO THE CONTROL ARM WHEN THE PH INTHE TEST ARM WAS 1.8 LESS THAN IN THE CONTROL ARM. (4)THESE AVOIDANCE PH LEVELS ARE HIGHER THAN THE LETHAL LEVELS FOR EACH FISH SPECIES REPORTED IN OUR PREVIOUS PAPER. IT IS SUGGESTED THAT THESE FISH CAN AVOID ACIDIFIED WATER MASSES BEFORE BECOMING ENTRAPPED.

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