FISHES 129 



realize; their study is of great value in preventing 

 the destruction of our fisheries by the pollution of 

 the waters and by over-fishing. 



Since fish are the animals of greatest economic 

 importance found in the sea, a whole section has been 

 devoted to a consideration of their characteristics. 

 In this chapter will be presented, in a rather abridged 

 and simplified manner, the more important and 

 interesting facts concerning the physiology, life 

 history, and habits of fish. 



Characteristics of Fish 



What is a fish? This question immediately brings 

 to mind animals that live in the water. However, all 

 that glitters is not gold; similarly, all animals that 

 live in the water are not fish. Our definition, there- 

 fore, must be so worded that it will include only 

 those aquatic animals which form the subject of 

 this chapter and which, for present purposes, we may 

 call true fish. This group of animals may be briefly 

 defined as cold-blooded creatures w^ith a backbone, 

 with legs and arms represented by fins or rudiments 

 of fins, and living in the water in which they breathe 

 by means of gills. This definition excludes many 

 forms frequently called fish, as for example the 

 oyster and clam, which are often spoken of as shell- 

 fish. It also excludes the starfish and the jellyfish, as 

 none of these animals have a backbone. The whales 

 and their allies are excluded because they have lungs 

 and do not breathe by means of gills. 



It is utterly impossible to describe the shape or 

 form of the body in answer to the question. What is 



