This paper records some observations on the reactions of minnows to phenolic substances. The fish are placed in a horizontal tube, half of which is filled with flowing water and half with flowing solution of the concentration to be tested. Water and solution are very sharply differentiated.
Solutions of phenol, ortho- and para-cresol are highly toxic and appear to have some specific effect on the nervous system of fish, causing them to lose their sense of balance and capability of co-ordinated movement. The time the solutions take to produce this effect is much shorter than the survival time; in a 0.01% solution of para-cresol, for example, a minnow loses its sense of balance in about 70 sec. but takes about 30 min. to die.
Over the concentration range 0.04-0.0004% minnows appear to have little or no power of discriminating between phenol and water, swim into the solution and become intoxicated.
At concentrations of 0.03-0.04% minnows will avoid para-cresol and ortho-cresol solutions immediately and escape intoxication. At somewhat lower concentrations the fish venture into the solution, and this quickly destroys their capability of recognizing and avoiding it. The situation is markedly different from that observed in the case of lead and zinc salts; here the time the fish takes to establish an avoiding reaction to the solution is very much shorter than the time this takes to destroy its capability of doing so.
- Copyright © 1951 The Company of Biologists Ltd.