STREAM POLLUTION 
405 
GOLDFISH 
Goldfish of any size up to 6 inches are easily obtainable in quantity from com- 
mercial goldfish farms, are relatively inexpensive, and stand shipment well. The 
practical considerations, although important in the selection of a test animal, are 
of course secondary to the physiological characteristics of the goldfish which make 
it particularly suitable for the bioassays of stream pollutants. The goldfish is 
tolerant of confinement and can be kept in laboratory containers and aquaria for 
months, making both short-time and long-time tests, uncomplicated by excitement 
and the attendant endocrine disturbances, possible under controlled conditions. 
The amount of oxygen consumed by the goldfish is not large per unit of weight, and 
tills fish does not succumb to low oxygen as quickly as many other fresh-water 
fishes. In fact, the uninjured goldfish if permitted can obtain sufficient oxygen to 
maintain itself for some time in water very low in or even devoid of dissolved oxygen 
merely by skimming and breaking the surface film of the water. Because of these 
facts, the toxic action of many substances which would be volatilized or oxidized by 
the constant aeration of water required to maintain various other species of fish 
can be ascertained, using goldfish as reagents; and the specific parts played by the 
oxygen demand, the external action, and the internal effects of the pollutant on the 
fish determined separately. On the other hand, if the combination of anoxemia and 
toxic action of the pollutant are desired, goldfish can be placed in closed containers, 
or merely prevented from reaching the surface layer of the water by submerged 
strips of glass which do not interfere with either the movement of the water or with 
its surface reaeration. 
By comparative tests the relative resistance of the goldfish to poisons, injury, 
and anoxemia was found to be equal to or greater than that of bass, perch, or catfish, 
and definitely greater than the resistance of trout or most fresh-water minnows. 
The minimal lethal concentration of any effluent or pollutant for goldfish established, 
therefore, approximately the maximal concentration of that pollutant which ought 
not to be exceeded if any fresh-water fish were to survive in waters polluted with 
such effluent. 
An added advantage in the use of the goldfish as a test animal is the already 
large literature on this fish in both physiological and pharmacological fields, in which 
the usefulness of this animal as a bioassay reagent is well established (Munch, 1931; 
Powers, 1917). 
The stock goldfish used for these tests were obtained in lots as needed from a 
commercial goldfish farm, and were held in flowing water in large hatchery tanks at 
a temperature ranging from 17° to 21° C. All goldfish were of the standard carp- 
form variety, i. e., the various ornamental varieties were excluded. The fish were 
fed regularly every third day a ration of prepared shrimp meal, and Myriophyllum 
growing in the tank was available at all times. For routine tests 3-inch goldfish 
(60 to 90 millimeters in length), weighing between 3 and 5 grams, were selected as 
standard. Larger sizes were used for special tests as required. 
