CHARACTERISTICS OF MARINE FISHES 171 



stream through rapids and falls, wearing themselves out in the process. When 

 they finally reach the spawning grounds, their fins are frayed and sometimes some 

 of their scales are missing. In short they are so exhausted that they die soon after 

 spawning. The Atlantic salmon, Salmo solar, also migrates to fresh water to 

 spawn, but unlike the Pacific salmon, it does not ascend long streams and does 

 not die after spawning. In fact the same individual may return several times. 

 Shad, alewives, smelts, and a few others also migrate from the ocean to carry out 

 their reproductive processes. It is evident that they enter fresh water solely for 

 that purpose as they usually do not feed during the migration and return to the 

 sea almost immediately after spawning. 



Fish that come from the sea and enter fresh water to spawn are said to be 

 anadromous. The young of most of the anadromous fishes remain in fresh water 

 only during their first stimmer and then follow the course of their parents to the 

 sea. However, most of the salmon remain longer. 



The migrations of fresh-water eels, Anguilla, are scarcely less wonderful than 

 those of the Pacific salmon. However, these eels reverse the migration, for they 

 leave the fresh water and "run" out to the deep sea to spawn. The chief spawning 

 ground of the American eel is a region to the southwest of Bermuda, while that of 

 the European eel may be a little further east and south, though probably over- 

 lapping. It is believed that fresh-water eels, like the Pacific salmon, spawn only 

 once and die when the act is completed. 



Fish that migrate from fresh water to the sea to spawn are said to be catadro- 

 mous. The young eels, which are flat and more or less ribbon-shaped, are known 

 as leptocephalus. They do not seem to tarry long in the spawning grounds, but 

 soon undertake the migration to their home in fresh water. As the young of the 

 American eel have only about a thousand miles to travel, they make the journey in 

 about a year. However, since those of the European eel have to travel about three 

 times as far, they require nearly 3 years. It is interesting that both the American 

 and European eels remain in the leptocephalus or larval stage, regardless of age, 

 until they reach the shallow shore waters, where they undergo the metamorphosis 

 and then enter fresh water as young adults. 



Although all fish do not make long journeys to carry out their reproductive 

 processes, most of them do spawn in definite areas. For example, the so-called 

 gray trout, Cynoscion regalis, is common in the harbor and estuaries of Beau- 

 fort, N. C, during the spring while the roe is developing. However, when nearly 

 mature the large breeding fish disappear from inshore waters. At that time 

 they "run" out to sea a short distance, deposit their eggs and milt, and in a few 

 weeks' time some of them, at least, return to the inshore feeding grounds. Other 

 species, such as the codfish, migrate to rather shallow water to spawn. In general 

 fish migrate to those areas where favorable physical conditions for the young 

 exist and where the food required by the larvae is normally present. Certainly, the 

 critical stage in the life of a fish occurs when it has used up the yolk retained 

 from the egg upon hatching and must begin feeding wherever it happens to be. 

 If the minute organisms required by most marine fish are not immediately at 

 hand, the larva of course perishes. 



Migrations to the feeding ground are carried out more or less regularly. Such 

 migrations are often closely associated with temperature. Thus, each autumn 

 croakers or hardheads, Micropogon undulatus, leave Chesapeake Bay in great 



