320 



FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE 



torn, the young become distributed to some extent 

 in the upper layers after hatching and are taken 

 also at the surface with tow nets, but most of them 

 remain on the bottom. 



Growth. — The rate of growth of this species is 

 as yet unknown, no special study having been 

 made based on a sufficient amount of material. 

 Hildebrand and Schroeder (1928 : 166) by measur- 

 ing a limited number of avai]al)le specimens give 

 tentative figures for growth as being 4I/2 to 7 

 inches at 1 year and about 10 inches at 2 years. 

 The age at which the fish mature is likewise un- 

 known. Hildebrand and Cable state (1930: 475) 

 that individuals with roe which have been ob- 

 served were large, KJi/o to 29 inches. The age of 

 specimens of that size is unknown at present. 



Migration. — During the warmer months of the 

 year, between April or May and November or 

 December, depending on the latitude, this species 

 is readily taken in comparatively shallow water, 

 generally between 2 and 20 fathoms. With the 

 advent of cold weather it becomes scarce in shallow 

 water, indicating a general migration of the 

 fish to deeper water. During the winter months 

 it may be taken in large numbers beyond the 20 

 fathom line (Pearson 1932) and down to 100 

 fathoms ( Schroeder 1931 ) . This migration is evi- 

 dently induced by the inability of the fish to 

 withstand the colder temperature of the more 

 shallow water. Fish sometimes are found torpid 

 in shallow water during the winter (Baird 1855), 

 probably being trapped by a sudden chill after 

 Ijeing lured from greater depths by a spell of 

 warm weather. The movement to deeper water 

 during cold weather is a common habit of various 

 species of fish. In the case of the summer flounder 

 this is apparently also a spawning migi-ation. The 

 fish appear again in shallow water during the 

 spring of the year, the time of appearance vary- 

 ing with the latitude, and most probably also with 

 the temperature conditions during any given year. 

 Other mass migrations of the adidts are unknown, 

 and it is unlikely that the species makes any other 

 general migrations. The summer flounder is prob- 

 ably a comparatively immobile fish as a species. 

 The young fry after hatching remain chiefly on 

 the bottom, but they become also distributed in 

 the upper layers to some extent, as stated. The 



fry undertake a movement from offshore to the 

 inner waters. After the young fish exceed a 

 length of 10 mm. they stay on the bottom and 

 continue to move inshore, many going into the 

 estuaries of rivers for considerable distances. The 

 young evidently remain at the brackish-water zone 

 and grow till they reacli a length of about 125 mm. 

 when they seem to gradually spread toward salt 

 water. 



Food mid feeding hahit>t. — The summer flounder 

 is primarily a predaceous fish. Its food consists 

 chiefly of such species of fish and small inverte- 

 brates as are readily accessible in the region which 

 it inhabits. The following fishes have been re- 

 ported as being preyed upon by the summer floun- 

 der, namely, mackerel, menhaden, tautog, sand 

 launce, silversides, butterfish. and scup; of in- 

 vertebrates, crabs, shrimp, squitl, small mollusks, 

 worms, and sand dollars. In the business of ob- 

 taining food it is aided by its ability of i^artial 

 concealment; by simulating the color of the back- 

 grovmd, by partly burying itself in the bottom, and 

 by the natural flat shape of the body. It lies flat 

 on the bottom, often partly buried in the sand or 

 mud, with the light and dark shades of color of 

 the uppermost surface so varied in intensity on 

 different parts of the body as to blend and har- 

 monize with the background. The instinctive 

 concealment is often so well accomplished that it 

 is quite hard to detect the position of the fish even 

 when keeping a sharp lookout in fairly cl«ar 

 water. It thus waits till some unwary victim 

 chances its way when it strikes with swiftness 

 and force. Sometimes it will pursue schools of 

 small fish to the very surface. 



Raeeft. — While it is not the primary aim of this 

 investigation to elaborate in detail the characters 

 which may be used in separating races, and, more- 

 over, the material at hand is not sufficient for a 

 thorough racial analysis; it is yet desirable to 

 point out the bearing of the characters investi- 

 gated on the study of racial differentiation. The 

 material examined yields evidence that the popu- 

 lations of Petredirhthys denfatiis from Chesapeake 

 Bay and from Beaufort, N. C, belong to two dis- 

 tinct racial stocks. The frequency distributions 

 of the meristic characters given in tables 2 to 6, 

 segregated by locality, for dentatu-s, are as follows: 



