Food of Fishes 235 



gathering and fastening together bits of vegetation. 

 It is built in the tops of the weeds — not on the pond 

 bottom. The nest is roughly spherical, with a hole 

 through the middle of it from side to side. Within the 

 dilated center of the passageway the female lays her 

 eggs: the male stands guard over the nest. After the 

 hatching of the eggs he still guards the young. It is 

 said that when the young too early leave the nest, he 

 catches them in his mouth and puts them back. The 

 stickleback lays only about 250 eggs. 



Thus in their extraordinary range of fecundity the 

 fishes illustrate the wonderful balance in nature. For 

 every species the number of young is sufficient to 

 meet the losses to which the species is exposed. 



The food of fresh-water fishes covers a very wide 

 range of organic products ; but the group as a whole is 

 predaceous. A few, like the goldfishes and golden 

 shiners, are mainly herbivorous and live on algae and 

 other soft plant stuffs. Others like carp and gizzard- 

 shad live mainly on the organic stuffs they get by 

 devouring the bottom ooze. Many, either from choice 

 or from necessity, have a mixed diet of plant and animal 

 foods. But the carnivorous habit is most widespread 

 among them. In inland waters they are the greatest 

 consumers of animal foods. 



Such fishes as the pike which, when grown, lives 

 wholly upon a diet of other fishes, are equipped with an 

 abundance of sharp raptorial teeth. The sheepshead 

 has flattened molar-like teeth strong enough for crushing 

 shells and adapting it to a diet of molluscs. Other 

 fishes, even large ones like the shovel-nosed sturgeon, 

 have close-set gill-rakers. These retain for food 

 the plancton organisms of the water that is strained 

 through the gills. The young of all fishes are plancton 

 feeders. 



