It seems to be one of the desiable properties of anesthetics that the fish should be anesthetized by them within a short time, and the long lasting anesthetization in their solutions should never bring the fish high mortality. With this view in mind, the authors have studied the relation between the concentration of anesthetic solution and the time required to induce deep anesthesia in
Hypodytes rubripinnis, and the relation between the concentration leading to 50% mortality of the fish and the duration of anesthetization. The anesthetics used in this study were tricaine methanesulfonate (M. S. 222), urethane and tertiary amyl alcohol.
In cases of urethane and tertiary amyl alcohol, linear regressions in log- log diagrams were obtained between the time necessary to induce deep anesthesia in the fish and their concentrations. However, no similar relation could be obtained by using M. S. 222, the dilution of M. S, 222 accerelating the fall of narcotic potency more than those observed in other anesthetics, though its narcotic potency is stronger than the others. These facts suggest that M. S. 222 is suitable for handling fish within a short time, but not for long lasting anesthetization, for which purpose, urethane seems to be more appropriate (Fig. 1).
From experiments on narcotic potency of M. S. 222 under various conditions, in comparison with urethane, the causes which bring about special characteristics of M. S. 222 as an anesthetic are considered as follows:
(1) Sea water is acidified by M. S. 222 dissolved (Fig. 2), and the more the solution is acidified, the stronger the narcotic potency of M. S. 222 becomes (Fig. 3).
(2) As campared with the other anesthetics, the solution of M. S. 222 decreases rapidly in concentration due to adsorption and absorption to the fish bodies during anesthetization (Fig. 6).
(3) For a time just after dissolving M. S. 222 in sea water, free carbonic acid liverated as a result of acidification of sea water makes the solution more acid, which causes a temporal increase in narcotic potency of the solution and the liverated carbonic acid itself act contributorily in the increase in narcotic potency (Fig. 8).
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