SMOOTHBACK FLOUNDER; EELBACK; FOOLFISH; CHRISTMAS FLOUNDER; PLAICE
[Jordan and Evermann, 1896-1900, p. 2650.]
This flatfish is right-handed (eyes on the right side) and small-mouthed like the winter flounder, yellowtail, and the witch. It resembles the winter flounder (with which it is often caught) closely in its general outline and in [page 284] the considerable thickness of its body. But it is distinguishable from the winter flounder by the fact that the skin of its head between the eyes is smooth and scaleless. Females are more easily recognized than males, their bodies also being smooth to the touch on both sides; males are nearly as rough skinned on the eyed side (except between the eyes) as the winter flounder, but they have much longer pectoral fins than the latter. Both sexes have fewer anal fin rays (only 35 to 40) and dorsal fin rays (about 56), too, while the caudal fin of the smooth flounder is narrower and more rounded than that of the winter flounder.
The smooth flounder can always be separated from the yellowtail by the facts that its very prominent lateral line is straight, not arched, that the dorsal (left) profile of its head is straight, not concave; and that it has fewer fin rays. It has little more than half as many dorsal and anal rays as the witch, and its long fins are highest midway of the body and tapering toward the head and tail, whereas they are nearly uniform in height from end to end in the witch. It lacks the mucous pits that are so characteristic of the blind side of the head of the latter, a convenient field mark for separating these two species.
The smooth flounder is peculiar among our local flatfishes for its sexual dimorphism. Besides the difference in the scales of the two sexes noted above, the pectorals on the eyed side are longer (about four-fifths as long as the head) and more pointed on the males than they are on the females.
The smoothback varies from grayish to dark muddy or slaty brown above, or to almost black, either uniform or variously mottled with a darker shade of the same tint; the dorsal, anal, and caudal fins are of the general ground color. These fins were mottled darker or paler, in specimens we have examined, but Storer described them as black spotted. The blind side is white.
This is the smallest flatfish that is common in the Gulf of Maine, for it grows to a maximum length of only about a foot, and to a weight of about a pound and a half.
This flatfish is confined to the close vicinity of the coast throughout its geographic range, occurring chiefly in estuaries or river mouths, and in sheltered bays and harbors; mostly on soft mud bottom. Correspondingly, it is found from tide line down to a maximum depth of perhaps 15 fathoms, with 2 to 5 fathoms as its zone of greatest abundance in our Gulf.
It prefers soft bottom to hard; so much so that a seine haul on soft mud yielded 23 smooth flounders to 4 winter flounders in St. Mary Bay, whereas another haul, only 100 yards or so distant, but on harder bottom, brought in only 3 smooth flounders to 189 winter flounders, as we learn from Dr. Huntsman's notes.
The shoal water habit of the smooth flounder exposes it to temperatures close to the freezing point of salt water in winter, and as high as 60° in summer, and perhaps higher temperatures still in some places. Little more is known of its life. But its small mouth suggests a diet similar to that of the winter flounder, and Kendall found that young fry 3 to 4 inches long from Casco Bay has been feeding chiefly on small crabs, shrimps, unidentified crustaceans, and polychaete worms.
Winter is its breeding season, females nearly ripe having been taken in Salem Harbor in December and spent fish at Bucksport, Maine, the first week in March, which corroborates fishermen's reports of more than half a century ago that it comes into Salem Harbor to breed at about Christmas time. It is not known whether the eggs sink or are buoyant, nor have its larvae been seen.
The smooth flounder is Arctic-boreal. It is definitely recorded from as far north as Ungava Bay, hence no doubt occurs along the Atlantic coast of Labrador; it is described as the most plentiful flatfish along the coasts of the Strait of Belle Isle at all seasons; its young are common in Pistolet Bay on the Newfoundland side of the Strait in shallow sunwarmed pools, and there are two specimens from the north shore of the Gulf of St. Lawrence in the Museum of Comparative Zoology (collected many years ago, labeled "Labrador").
Evidently it is widespread on the southern side of the Gulf of St. Lawrence, for it is the next most plentiful flatfish after the winter flounder on the Cape Breton shore and at the Magdalens, according to Cox; it is reported from Prince Edward [page 285] Island, also from Trois Pistoles; and it has been classed by Huntsman as characteristic of the estuarial transition from fresh to salt waters in the southern side of the Gulf of St. Lawrence generally. We find no record of it on the outer coast of Nova Scotia between Cape Breton and Cape Sable; but we suspect that it has been overlooked there, for it is widespread in the Gulf of Maine to Massachusetts Bay, as detailed below, and has been reported as a stray as far south as Providence, R. I.
Its range probably is continuous in the north with that of its polar relative (L. glacialis) of the Arctic coasts of North America and Siberia. Indeed, it is a question whether any valid distinction can be drawn between the two species.
The smooth flounder is to be found in estuaries, river mouths and harbors, all along the shores of the Gulf, from the Bay of Fundy to the northern side of Massachusetts Bay. Localities whence it has been recorded in print, or has been definitely reported otherwise, are Annapolis basin, Minas Channel and St. Mary Bay; Grand Manan; Bucksport at the mouth of the Penobscot River; Belfast in Penobscot Bay; Casco Bay; Portland; Salem Harbor; and Boston Harbor. Apparently the latter is the southern limit to its regular occurence for while there is a specimen in the Museum of Comparative Zoology, from Provincetown at the tip of Cape Cod, it seems to be unknown in Cape Cod Bay, along the outer shore of Cape Cod, or in the Woods Hole region, though a stray individual has been caught at Providence, R.I.
This flatfish (often confounded with the winter flounder) has been found so often in various markets among the winter flounders as to suggest that it is more plentiful along the coasts of northern New England, than is realized, generally.
In Casco Bay and in estuaries of the Bay of Fundy such as the mouths of the St. Croix and Annapolis Rivers it is abundant in summer, which no doubt applies equally to the intervening coast line. But it is said to run up into harbors in Massachusetts Bay in autumn and winter only; nor would such a local difference be astonishing in the case of a cold-water fish, which might well be driven out into slightly deeper water by summer heat in the southern and western parts of the Gulf, but not in the northern and eastern parts.
This is an excellent table fish for its size, sweet-meated and thick-bodied like the winter flounder. But it is neither large enough, plentiful, nor widely enough distributed in the open Gulf to be of any commercial importance.
 Jeffers, Contrib. Canadian Biol., N. Ser., vol. 7, No. 16 (Ser. A, No. 13, 1922, p. 210). There are specimens from St. Anthonys, northern Newfoundland, in the Museum of Comparative Zoology.
 Rept. Newfoundland Fishery Res. Comm., vol. 1, No. 4, 1932, p. 110.
 Contrib. Canadian Biol. (1918-1920), 1921 p. 113.
 Cornish, Contrib. Canadian Biol. (1906-1910) 1912, p. 81.
 Vladykov and Tremblay, Nat. Canad., vol. 62 (Ser. 3, vol. 6), 1935, p. 82; (many specimens reported).
 Trans. Roy. Soc. Canada, Ser. 3, vol. 12, Sect. 4, 1918, p. 63.
 This specimen, formerly in the Museum of Comparative Zoology, is no longer to be found.
 Our experience corroborates this to the extent that we have never seen it there in summer.