Pisces. 165 



But the eggs of many fishes are eaten by thousands by many 

 kinds of fishes and other animals. The very great num- 

 ber of eggs laid by most fishes is in keeping with the fact 

 that the chances are many to one against their success- 

 ful development. Indeed, if the eggs all developed, 

 it is easy to see that the ocean would be overrun. For 

 instance, the codfish is said to lay about eight million 

 eggs yearly ; if each of these eggs developed, it would not 

 take long literally to fill the ocean. Contrast this " infant 

 mortality" with that of the fulmar petrel. This is said 

 to be the most numerous bird in the world, though it lays 

 but a single egg; but the conditions are such that the 

 chances of this single egg for reaching maturity are ex- 

 tremely favorable. 



Migration of Fishes. The salmon, shad, and sturgeon 

 pass from the sea up rivers to spawn. The eels pass from 

 rivers into the sea to lay their eggs. Aside from migrat- 

 ing to find suitable breeding grounds, fishes migrate more 

 or less in search of food. With some kinds their move- 

 ments are pretty regular and well known ; in other cases 

 their location at any given season is very uncertain, depend- 

 ing on their food and other conditions not accounted for. 



Deep-sea Fishes. Most fishes are found near shore or 

 in comparatively shallow water. Of those found in deeper 

 waters, it is interesting to observe that, as the water be- 

 comes deeper, and the amount of light consequently less, 

 the fishes usually have larger eyes, or else a better develop- 

 ment of the organs of touch. In the deepest water many 

 are phosphorescent, and blind fishes, or fishes with rudi- 

 mentary eyes, are found. 



The Food Fishes. Among the principal food fishes are 

 the codfish, salmon, haddock, shad, mackerel, hake, smelt, 

 sardine, menhaden, mullet, lake trout, whitefish, sturgeon, 



