T^ Chapter Ten 



Fish Enemies 



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

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

 gator 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 scientific 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 essen- 

 tial in the summer season to be ever on the lookout for any of the 

 pests which may have gotten by our keenest observation. For- 

 tunately 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. 134. Water Tiger (Life size) 



of 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 



