CHARACTERISTICS OF MARINE FISHES 173 



On the other hand many species of marine fish are of comparatively limited 

 geographical distribution. For example, the sea bass, Centropristes striatus and 

 the common weakfish, Cijnoscion regalis range only from Cape Cod, Mass., to 

 northern Florida; the white perch, Morone americana, from Nova Scotia to South 

 Carolina; and the tautog, Tautoga onitis, from the Bay of Fundy to South 

 Carolina. These are all common food fishes. Many others from the same general 

 vicinity, as well as from other shores, could be named with a similarly restricted 

 range. Furthermore, the species named, as well as many others, are confined to 

 comparatively shallow water along the shore, which still further limits their range. 

 Then there are also some more or less obscure species that are known from only 

 a few specimens and from only one locality. For example, a species of menhaden, 

 Brevoortia hrevicaudata, although described in 1878, is still known only from 

 the 8 specimens originally described from Noank, Conn. 



Geographical distribution of fish has also been influenced in some areas by 

 geographical changes, which in some instances have removed barriers and in 

 others created new ones. An excellent example of the formation of a new barrier 

 is the elevation of the Isthmus of Panama. Not long ago, as geologists reckon 

 time, fish from the Atlantic and the Pacific oceans intermingled there freely. In 

 the course of time this passageway became closed, separating the representatives 

 of many species of fish. Since then some of the species have yielded slowly to 

 changes in environment, some not at all. Others yielded more quickly. The result 

 is that today a small number remain common to both coasts of Panama, whereas 

 the majority are separable by small, though not trivial, differences in their 

 anatomy. 



Physical and biological disturbances, too, have affected the distribution of fish, 

 at least temporarily. A case in point is that of the tilefish, Lopholatilus chamaele- 

 onticeps, abundant off the coast from Massachusetts to New Jersey prior to 1882. 

 In that year steamers arriving from Europe reported thousands of square miles of 

 the ocean's surface covered with dead tilefish, and thereafter this fish disappeared 

 from the markets. Some fish survived, however, and by about 1915 the species 

 had reestabhshed itself in commercial abundance. This catastrophe, it was de- 

 termined, was probably caused by Arctic ice that had been driven into the home 

 of the tilefish by northern winds and had made the water too cold for their 

 welfare. 



Spawning and Reproduction 



All fish, so far as knovm, have rather definite spavming seasons, as well as 

 definite spawning grounds. The season varies according to species, though the 

 vast majority spawn during the spring and early summer. However, more than 

 a few common commercial species, such as the cod, several species of flounder, 

 the common croaker, the menhaden, and others spavm during the fall and winter. 



The spawning grounds, which are also the feeding grounds of the newly 

 hatched fish, are extremely important. Conditions for the incubation of the eggs 

 must exist; and, equally important, the area must provide the proper temperature 

 and food needed to help the larval fish through the very critical stage when they 

 begin acquiring their own food. 



It was pointed out in a preceding section that some fish migrate to the shore 

 and some ascend fresh-water streams to spawn. Others, such as the weakfish. 



