DDT in dosages greater than 0.1 ppm. proved toxic to goldfish in laboratory tests. In field tests, surface applications of DDT as a dust and in oils were not harmful to fish in dosages used for mosquito control. Other cold-blooded aquatic animals, such as frogs, snakes, crayfish, spiders, and insects, were affected by suspensions of DDT. No harmful effects on warm-blooded animals were noted in applying DDT as a larvicidal treatment.