[Jordan and Evermann, 1896-1900, p. 520.]
The capelin is an even slenderer fish than the smelt, its body being only about one-sixth to one-seventh as deep and about one-twelfth as thick as it is long, and of nearly uniform depth from gill cover to anal fin (except in the case of females when their abdomens are distended with spawn), whereas the smelt is usually deepest about its mid-length (at least if the fish is fat), which gives the two species characteristically different aspects. The head of the capelin is pointed like that of the smelt, the mouth gaping back to below the center of the very large eye with the tip of the lower jaw projecting noticeably beyond the upper. The scales are minute, much smaller than those of the smelt and more numerous (about 200 per row on the sides of the body); the teeth so small as to be hardly visible to the naked eye, and the tongue fangs, so characteristic of the smelt (p. 135), are lacking here. The outline of the adipose fin likewise helps separate capelin from smelt, for it is low in the former and about half as long as the anal, but short and high in the latter. The pectoral of the capelin is broader also, usually with 15 or more rays.
The capelin exhibits a pronounced sexual dimorphism; the male has much the longer pectoral fins; and the base of his anal is elevated on a pronounced hump, whereas it follows the general outline of the belly in the female. In males, too, the scales in one of the longitudinal rows immediately above the lateral line, and in another row along each side of the belly, are pointed, distinctly larger than the other scales, and become longer still at spawning time when each pushes up the skin as a finger-like process; they form four ridges that are very evident when the fish is held in the hand.
The capelin is transparent olive to bottle green above, like a smelt, but its sides are uniformly silvery below the lateral line and the scales are dotted at the margins with minute dusky specks (in the smelt there is a distinct silvery band on each side); the belly is white. Back and head darken at spawning time.
Few capelin are more than 6½ to 7½ inches long.
Capelin are most in evidence during the spawning season, when they come inshore in multitudes along arctic-subarctic coasts. They spawn on gravel or pebbly bottom, chiefly close below tideline, many of them in the wash of the waves in the beach; many are stranded then on the beach between waves. But eggs have also been reported from as deep as 35 to 40 fathoms. Each female while spawning is accompanied by two males that crowd her between them; but she may have only one companion. Spawning takes place chiefly at temperatures of 43° to 50° F. (6°-10° C.) and more actively by night than by day.
The eggs are reddish, about 1/25-inch (1 mm.) in diameter, and so sticky that they cling to each other like herring eggs, and to the gravel and pebbles with which they are intermingled by the swash of the waves. They hatch in about 15 days at a temperature of 50° F. (10° C.). And they will tolerate a salinity as low as 7 per mille, [page 135] as Dr. Jeffers writes us. The larvae, described as 5 to 7 mm. long at hatching, are very slender and resemble those of smelt, herring, and launce so closely that identification is a matter for the expert. In any case, capelin are encountered so seldom in our Gulf that their larvae are not apt to be seen there.
Along the coasts of Newfoundland, capelin spawn chiefly in June and July, and we have found them doing so in multitudes along the outer Labrador coast in July. Probably any spawning that may take place within the limits of our Gulf would fall in May at latest, to judge from water temperatures.
The capelin so seldom appears in the Gulf of Maine that we need only add that it is a fish of the high seas frequently encountered far out from land, coming inshore only to spawn and then as a rule moving out again; that it travels in vast schools at spawning time (when it often strands on the beach in countless multitudes). It is the chief bait fish of Arctic seas, preyed upon by whales and by every predaceous fish, particularly by cod, which are often seen pursuing the capelin at the surface in northern waters. Capelin themselves feed chiefly on small crustaceans, particularly on copepods, on euphausiid shrimps, and on amphipods. It is also known to devour its own eggs. We can bear witness that the capelin is a delicious little fish on the table.
Boreal-Arctic seas, south to the coast of Maine on the Atlantic coast of America.
The capelin is a sub-Arctic fish that visits the Gulf of Maine occasionally; chiefly the eastern side as might be expected since it comes from the north.
Dr. Huntsman writes:
In the Gulf of St. Lawrence it occurs abundantly in limited areas, which shift somewhat from year to year. It occurs periodically in similar limited areas farther south. The southeastern corner of Cape Breton is the center of such an area, where large quantities were taken in 1917. Halifax is the center of another area, where, however, it is more rare. In 1916 it was abundant at Sambro, near Halifax. The next area is in the Bay of Fundy, where they have, exceptionally, been taken in large quantities at long intervals.
Apparently a period of this sort occurred about the middle of the past century, for Perley, writing in 1852, reported it from a number of points in the neighborhood of St. John, New Brunswick. It seems then to have disappeared from the Gulf of Maine, not to reappear until 1903 when it was common in the Bay of Fundy in May. A few were again taken off Passamaquoddy Bay in that same month of 1915. And this was the prelude to a period of local abundance, for capelin were noticed among the herring in the weirs of the Passamaquoddy Bay region in October 1916, becoming so plentiful by the end of November that one catch of 3,000 pounds of fish consisted of 2,000 pounds of capelin and only 1,000 of herring. They were also reported at various localities along the New Brunswick coast at that time. Probably they persisted locally in the Bay of Fundy throughout the winter of 1916-1917, for large numbers of capelin appeared in Minas Basin in the following May and June. We find no record of capelin within the limits of the bay in 1918, but they were taken again in 1919 in 50 fathoms of water off Passamaquoddy Bay in January, February, and March, and they appeared with smelts a month later as far west as the Penobscot River, penetrating far inland. None, however, have been seen in the Gulf of Maine since then, so far as we have been able to learn.
 Interesting accounts of the habits of the capelin and of its rate of growth in Newfoundland waters have been given recently by Jeffers (Ann. Rept. Biol. Board Canada (1930), 1931, pp. 7-18); by Sleggs (Rept. Newfoundland Fish. Res. Comm., 1, No. 3, 1933); and by Templeman (Bull. Newfoundland Government Lab., 17 (Research), 1948.
 According to Lanman, Rept. U. S. Comm. Fish. (1872-1873) 1874, p. 225.
 Templeman (Bull. Newfoundland Government Lab., 17, Res., 1948, figs. 18-20) gives a series of excellent illustrations of capelin larvae at different stages of growth.
 According to Jordan and Evermann the capelin finds its southern limit at Cape Cod, but we find no actual records of its occurrence further south than is mentioned.
 Quoted from a letter.
 Huntsman (Contrib. Canadian Biol., (1921) 1922, p. 50) and Kendall (Copeia, No. 42, 1917, pp. 28-30; and Copeia, No. 73, 1919, pp. 70-71) give details.