CHAPTER FIVE 



Fish Enemies 



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Among the troubles that beset the fish culturist, not the least are 

 caused by insects and their larvae. This applies both to the propagator 

 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 detec- 

 tion 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 three, all of them being larvae. 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. 



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 



Fig. 71. Water Tiger (Life size) 



of young fishes. It does not idly 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 



