162 GOLDFISH VARIETIES AND 
rounding a mouth. The shape varies so amazingly that an accurate 
description is impossible. The two figures shown in Figure 113 are of the 
same individual. When alarmed the tentacles are entirely withdrawn, 
making recognition still more difficult. 
They rapidly deplete an aquarium of daphnia and newly hatched 
fishes. When a school of fry under 5-16 inch long is disappearing with- 
out apparent cause, it will be well to take a sharp look for some harmless 
looking hydra. 
Hydra possess a poison which quickly stupifies their prey, and to fish 
large enough to eat the hydra this poison doubtless has an unpleasant 
taste. There is no fish known which will eat them. To get rid of this 
pest, remove all fish, snails, etc., from the tank and place in it a solution 
of permanganate of potassium of a strength of 3 grains to the gallon of 
aquarium water. Allow this to stand for two days, change water and 
replace fish. This treatment will not kill plants. 
If no small living food be placed in the aquarium, hydra will in a 
few weeks be starved. 
One experimenter has claimed that by raising the water temperature 
to 110° Fahrenheit for a few minutes the hydra will all be killed, while 
the plants will not be affected. 
LARGER ENEMIES OF FISHES 
It should not be understood that the foregoing are the only serious 
enemies of pet fishes. In the greenhouse, outdoor pool, or even the 
library, misfortune is liable to descend in various guises. Chief among 
these are the cat, rat, muskrat, snake, heron, kingfisher and small boy. 
Fishes are also taken by the large frog, sandpiper, horned: owl, crayfish, 
and blackbird. The latter specializes on picking out the eyes of telescope 
fishes if the water is near enough to the edge of tank for him to reach 
them. 
