[Jordan and Evermann, 1896-1900, p. 745.]
The nine-spined stickleback is a slender little fish five to 6 times as long (not counting the caudal fin) as it is deep, with a very slim caudal peduncle. The latter usually has a well-developed longitudinal keel on either side; but this keel may be very low or even wanting. There are no bony plates along the sides of the body, but only along the bases of the anal and dorsal fins and on the caudal keels. There are no true scales. The most distinctive character is that there usually are 9 spines on the midline of the back (from 7 to 12 have been counted) in a continuous row from close in front of the pectorals to the dorsal fin, set in a slightly zigzag line and leaning alternately to one side and to the other. The spines are weakly curved rearward; wider at the base than at the tip; fairly uniform in size; about one-half to one-third as long as the height of the dorsal fin; each has a small triangular fin membrane at its base; and there is a shallow groove along the back, into which the spines can be depressed. Each ventral fin is represented by a stout curved spine thicker and longer than the dorsal spines. The dorsal and anal fins (the former stands above the latter) are alike in form, tapering from front to rear, the anal preceded by a single stout recurved spine. The tail fin is weakly rounded.
Large adults are seldom more than 3 inches long, more commonly 2 to 2½.[page 308]
Usually dull olive brown above, the upper part of the sides faintly barred or blotched darker; the belly silvery; the pubic and thoracic regions often black. The color varies, however, with the season of the year, with the state of sexual maturity, and with the color of the bottom on which the fish is living, those on dark mud being darker and those on bright sand paler. All become more brilliant during the breeding season when reddish tints appear under the head, the belly turns greenish, and black dots develop here and there over the entire body. The male has also been described as assuming a rosy tint beneath.
Since the range of the nine-spined stickleback hardly touches the open waters of our Gulf, We need only note that its mode of life is much the same as those of its three-spined relative next to be considered (p. 308); that it is similarly destructive to the spawn and young of other fish, and similarly pugnacious. Probably it spawns in summer on the shores of the Gulf, for its breeding season in northern Europe covers June and July. The male often (but not always) builds a nest attached to grass or weeds which the female spawns, and he guards nest and eggs until the latter hatch, which occurs in about 12 days.
This is one of the most widely ranging of northern fishes, occurring both in fresh water and in salt in the northern parts of both hemispheres; from northern Scandinavia to France, the western Mediterranean and the Black Sea on the European coast; from Arctic seas south to New York along the American, and westward to Saskatchewan and Alaska.
This stickleback is to be found all around the shores of the Gulf of Maine from Nova Scotia and the Bay of Fundy to Cape Cod, but it is chiefly restricted there to harbors and the creeks in salt marshes, where large numbers may often be taken in company with the mummichogs that swarm in such locations, and where it is to be found throughout the year. It is also found in fresh water. In fact, the most exposed situations around the Gulf, where we have heard of it, are Biddeford Pool, Maine, Passamaquoddy Bay, and St. Mary's Bay on the west coast of Nova Scotia.
This stickleback is of no commercial importance in America, but it is sometimes tried out for oil in northern Europe when enough can be caught.