THE REACTIONS OF FISHES TO TOXIC SUBSTANCES-III

THE REACTIONS OF FISHES TO HYDROGEN ION

Abstract

Several investigators have observed the behavior of fishes in acid gradients^1)-6). No one succeeded, however, to associate the behavior of fish with concentrations of hydrogen ion because of either interfering action due to carbonic acid resulted from adding strong acid to natural water or complexity of acid gradients owing to the structural defects of their test tank. Hence, the author attempted to study the reactions of fishes to hydrogen ion excluding such troubles as mentioned above. A newly designed gradient tank (Fig. 1) was used in this study for establishing gradients of concentrations of hydrogen ion in horizontal way but not in vertical way. The usual buffer of bicarbonate and carbonic acid in test water was previously replaced by a buffer of mono-and dibasic phosphate for removing the interference of carbonic acid. This water was supplied to the tank in such way as illustrated in Fig. 1. Usually eleven fishs were placed in it and acclimatized overnight. Then 0.025N hydrochloric acid was injected to the test stream. The behavior of fish was checked every two and half minutes during the test periods of 4 to 6 hours. The concentrations of hydrogen ion were measured at appropriate intervals by a glass electrode pH meter on sample water from seven positions of the tank. Minnow, carp, wild goldfish, goldfish bitterling and dace were employed as test animals. Their scientific names and other experimental conditions were detailed in Table 1.
In Figs. 2 to 7, the upper limits where fish were able to approach against, and then avoid of, concentrations of hydrogen ion are represented with a thin line, the mean positions where most of fish took refuge are also represented with a bold line, and the distribution of pH are indicated with iso-pH chain lines. The relationships between pH values and avoidance frequency obtained statistically from these Figs. are summerlized in Table 2. The data reveal that the limiting pH values which fish avoided with frequency of 100% range 2.75 to 3.40, the mean pH values which fish avoided with frequency of 50% range 4.20 to 5.95, and another limiting pH values which fish began to avoid with frequency just corresponding to 0% range 5.20 to 6.80. The data also show the fact that fish mostly take refuge in water with pH values higher than 6.0 after avoiding lower pH regions. In Fig. 8, the relationships between avoidance frequency and pH values are shown graphycally. When the avoidance frequency is expressed in cumulative percentage, the relation is almost linear as indicated with dotted lines except one case of bitterling. Therefore, this gives the relation of equation (1)
dF/dpH=k'••••(1)
and there are next relations; dpH=-d log [H⁺]=-0.4343•d ln [H⁺]=-0.4343•d[H⁺]/[H⁺].
Therefore, equation (1) gives equation (2).
dF/d[H⁺]=k/[H⁺]••••(2)
where dF is the change of avoidance frequency, d[H⁺] is the unit change of concentration of hydrogen ion, and [H⁺] is the surrounding concentration of hydrogen ion. Apparently equation (2) represents Weber-Fechner's law in psychology. Although avoidance behavior of fishes have seemed to obey All or None law in physiology as supported by some data^3)-50 which assigned narrow ranges or constant values to the avoidance concentrations of strong acid, the broad regions of avoidance pH in Table 2 and the relation of equation (2) prove that the avoidance behavior of fishes to hydrogen ion obey Weber-Fechner's law. We can define the discriminatory sensitivity of fish to concentrations of hydrogen ion as dF/d[H⁺].