437 



Teleosts differ very much in the nature of their food and in their manner of' 

 securing it. Some, like the Catfish, Sturgeon and . Suckers, are bottom feeders, 

 and such are often furnished with protractile lips, the better to secure the mol- 

 luscs, worrrs, aquatic insect-larvae or fish-spawn on which they live. Others, 

 like the Whitefish, are dependent on the crustacean life with which our fresh waters 

 swarm, (fig. 9), the young living on the minute Entomostraca, the adult on the 



FIG. 9. 



Ascllus communis. x 2. 



Gammarus sp. x 3. 



Branchipus vcrnalis, 

 swimming on its back, x 3. 



Dapknia pulcx. x 18 



Cypris Candida. 



Cyclops sp. x. 12. 



larger shrimp-like forms. Others again, more agile, leap to secure the insects on 

 which they feed, while many are carnivorous, feeding on other smaller species of 

 fish. Unquestionably the microscopic life of the fresh waters is the prime source 

 of much of the food of our fresh water fishes, and most comprehensive investi- 

 gations are therefore being carried on in regard to the life of the larger bodies of 

 fresh water in Europe with the object of ascertaining the conditions which 

 appear favourable to the abundance of food-material of this character, and the 

 species which appear to contribute most to the sustenance of the fish. 



As the smaller species of fish serve as food for the larger rapacious forms, 

 which may thus be regarded as inimical to them, so also the various fish-eating 

 birds tind reptiles may be regarded as enemies of the class. There are, however, 

 some more insidious enemies which are deserving of mention the various fish- 

 eating insects, and the various parasites, animal and vegetal, which afflict fish. 



Amongst the former are specially to be noted the larger water-beetles, Dytiscus 

 and Acilius, which may completely devour small fish by the aid of their rapa- 

 cious jaw-e ; the larger and smaller water-bugs and water-boatmen, Belostoma, 

 Notonecta and Ranatra, which attack fish by grasping them with their power- 

 ful front legs and then sting them and suck their blood by their sucking 

 proboscis. 



