156 GOLDFISH VARIETIES AND 
INSECT ENEMIES OF FISHES 
Among the troubles that beset the fish culturists, not the least are 
caused by insects and their larve. This applies both to the propagators 
of food fishes and those interested in fancy aquarium pets. We use the 
term “insect” here in its popular sense and not according to exact scien- 
tific definition. 
Some of these enemies are much more readily detected than others, 
but most of them may enter the rearing tanks when so small that detection 
is practically impossible. Wire screen or netting will keep out those that 
fly, or a large enemy in the water can be separated from daphnia or other 
living food by passing the “catch” through a fine wire gauze under water, 
but despite these precautions it is essential in the summer season to be 
ever on the lookout for any of the pests which may have gotten by our 
keenest observation. Fortunately for the aquarist there are not many 
kinds of insect enemies with which he is actively concerned. There are 
only four, three of these being larve. While the others are none the less 
savage or fatal they are not so often met with, or else are so easily 
detected that they are not such serious factors with which to reckon. 
With the aid of illustrations made from specimens, mostly living, we will 
proceed to give descriptions of the four arch-enemies in the order of their 
destructiveness, and follow on with the others, adhering to the same plan 
as far as possible. 
Water Tiger. This is the larva of the Predaceous Diving Beetle 
(Dytiscus), itself also a very powerful but easily detected enemy. The 
Water Tiger is easily the most rapacious, savage and insatiable enemy of 
Fic. 99. Water Ticer (Life size) 
young fishes. It does not wait for its prey to pass nearby, but adopts 
business-like methods of going after its unwary victims. The flat head 
is furnished with a strong pair of hollow mandibles, through which it 
sucks enough blood to kill its victim and then wantonly goes after another. 
In this way a single individual may kill an entire hatching of fish over 
night. This larva can usually be recognized by its spindle-shaped body, 
