メダカ群集による毒水の解毒

抄録

The experiments which form the basis of the present report were conducted along the same line as done by ALLEE and BOWEN (1932) on the fixation of poison by goldfish populations. The material (25-27 mm in-length) was obtained from a water duct in the field and used for experiments after rearing for a week in the laboratory. As an environmental poison colloidal silver was employed. Tap water used as the solvent contained 0.00001 mg/cc NH_3,0.00164 mg/cc of Cl, with a pH 7.4. Unless otherwise stated, all the following experiments were carried out under the temperature range between 15.5°-16℃. First, effects of the colloidal silver suspensoid upon an isolated fish were tested, using 5 units for each of the various concentrations shown in Table 1. The results (Table 2) were fairly fluctating, but the average showed rather reliable correlation between the colloidal silver consentration and the life duration (Fig. 1). According to the result, a 4.374 mg/cc concentration was adopted as a standard strength of the poison. In the chief experiments, 4 series of populations which were composed of 5,10,15 and 20 individuals respectively, each with 3 units, were subjected to a 200 cc of poison of the above mentioned concentration. The results, as set out in Fig. 2,clearly demonstrated that the greater the number of the fishes, the longer was their life duration. We then measured the quantities of the silver precipitated by each series of populations and obtained a result (Fig. 3) which showed that the fixation of silver per one fish was about 0.011 mg, with the exclusion of the exceptional result of the series consisting of 5 individuals. According to the examination of the fishes poisoned to death, it was made clear that the gills were heavily covered with the precipitated silver. Probably the death of the fishes, in addition to the chemical virulency by the suspended sliver, was accelerated by such a mechanical obstruction on the respiration. Further experiments concerning the temperature effects on the conditioning of the environmental poison indicated that a unit of 15 individuals exposed to 23℃ survied in an average much longer (162 min.) than the 5 control units (68 min.). In this case, it was also observed that at the temperature range between 16°-23℃, Q_<10>-rule could be applied to the increase in breathing number (108→190 per min., 10 min. after being exposed to the condition) and the decrease of the survival time (110→68 min.), while at a temperature of 13℃, this rule could not be proved true, for all the fishes in the virulent water lived even after 5 days when the experiment was stopped.