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Alligatorfish Aspidophoroides monopterygius (Bloch) 1786


[Jordan and Evermann, 1896-1900, p. 2091.]

Alligatorfish (Aspidophoroides monopterygius)

Figure 238.—Alligatorfish (Aspidophoroides monopterygius).Top and center, adult, side and dorsal views, Halifax, Nova Scotia; from Jordan and Evermann, drawing by H. L. Todd. Below, larva, 11 mm. long, Gloucester, Mass.


The readiest field marks for the identification of this curious little fish (so odd in appearance that it is not likely to be mistaken for any other) are that its entire head and body are clad with bony plates; that it has only one dorsal fin (the soft rayed); and that it is very slender (about 12 to 13 times as long as it is deep, not counting the caudal fin), rather broader than deep, and tapering rearward from the head to a very slender caudal peduncle. The plates are smooth, arranged in longitudinal rows. There is a double row along the back running from close behind the head to close behind the dorsal fin where it unites into a single mid-dorsal row (altogether 45 to 50 double and single plates along the back); three rows on the forward part of each side, but only two rows along the rear part; and two rows along the lower surface to just behind the anal fin, where they unite in one row. Thus the trunk is octagonal in front of the unpaired fins, but hexagonal behind [page 458] them. There are likewise two large plates and several small ones in front of each pectoral fin. The eyes are very large, with prominent ridges above them, and there are two sharp recurved spines on the top of the nose. The mouth is small with minute teeth. The dorsal and anal fins (each of five or six rays) are fanshaped, one over the other, and are situated about midway of the trunk. The caudal fin is small and rounded, the pectorals are larger than the anal, dorsal, or caudal fins, and the ventral fins are reduced to one spine and two rays each.


The many specimens we have seen have been dark brown above, lighter brown below, with two darker cross bands between the pectoral fins and the dorsal fin; one cross band under the dorsal, and two or three cross bands between the dorsal and caudal fins. The dorsal and pectoral fins are more or less barred; the caudal is dusky.


Five to seven inches long when full grown.


Nothing whatever is known of the life of the alligatorfish except that it is a bottom fish and that it has been repeatedly found in the stomachs of cod, haddock, and halibut although it is not "much thicker or softer than an iron spike."[18] The Grampus and the Albatross II have trawled it both on pebbly bottom, on sand and broken shells, and on soft mud. So far as known adults never stray into water shoaler than 10 to 15 fathoms, and the deepest record for it, with which we are acquainted, is from 104 fathoms.[19] Its range shows that it is a cold water fish. Its upper temperature limit is about 50°-52°; its lower limit close to the freezing point of salt water. Its breeding habits are unknown. Probably its eggs sink like those of sculpins.

The presence of its larvae in Passamaquoddy Bay, off Boothbay, and near Seal Island, Nova Scotia, from April to June, points to late autumn and early winter as the spawning season. It does not take to the bottom until of considerable size, for we have taken young ones as long as 29 mm. in our towings.[20]

General range—

From west Greenland and the east coast of Labrador southward to Cape Cod, and to northern New Jersey as a stray.

Occurrence in the Gulf of Maine—

Being of no interest to fishermen, and living too deep to strand on the beach, this fish is seldom reported. It has been taken in the Bay of Fundy in 15 to 100 fathoms; in the inner part of Passamaquoddy Bay; near Eastport; off Mount Desert in 60 fathoms; off Monhegan; near Portland; in 30 fathoms off Casco Bay; on Cashes Ledge; in Ipswich Bay; off Gloucester, Nahant, and Boston in Massachusetts Bay; off Provincetown; off Chatham; and in the South Channel to the eastward of Cape Cod. Evidently it may be expected anywhere in the Gulf in depths of 10 to 100 fathoms, and perhaps deeper.

Goode and Bean[21] described it as "abundant" in the deeper parts of Massachusetts Bay, but our [page 459] experience on the Grampus suggests "not uncommon" as a better description, for our largest catches were 8 specimens from 32 fathoms in Ipswich Bay; 6 specimens from 27 fathoms in the inner part of Massachusetts Bay; and 14 specimens off Chatham, in May 1930, from 28 fathoms.

Other recent catches in various parts of the Gulf have been of 1 or 2 fish each. And the fact that we found it at only 4 out of our 10 trawling stations of 1912 (all in the western part of the Gulf) is in line with Huntsman's statement that it is found only occasionally in the Bay of Fundy.

It is perhaps more plentiful along the Nova Scotian shelf eastward and northward from Cape Sable.[22] It is numerous enough in the southern part of the Gulf of St. Lawrence for Huntsman[23] to describe it as "characteristic" of the ice-cold Banks water there; it has been reported in the estuary of the St. Lawrence River near Trois Pistoles;[24] and at several localities along the west coast of Newfoundland. It is so widespread over the eastern half of the Grand Banks, along eastern Newfoundland, and off southeastern Labrador that it is listed at 14 stations there from the experimental trawlings of the Newfoundland Fisheries Research Commission[25] and is reported from Hamlton Inlet.[26]

The only records of it to the westward of Cape Cod are of the head of one that was dredged off Watch Hill, N. J., in 1874;[27] and of one that was taken off Sandy Hook, N. J., in 1864.[28]

[18] Goode, Fish. Ind. U. S., Sect. 1, 1884, p. 258.

[19] Southeastern slope of Browns Bank, latitude 42°20' N; longitude 65°08' W; Goode and Bean Smithsonian, Contrib. Knowl., vol. 30, 1895, p. 284.

[20] Bigelow, Bull. Mus. Comp. Zool., vol. 61, 1917, p. 272.

[21] Bull. Essex Inst., vol. 11, 1879, p. 13.

[22] Vladykov and MacKenzie (Proc. Nova Scotian Inst. Sci., vol. 19, 1935, p. 97) describe it as "very common" there.

[23] Trans. Roy. Soc. Canada Ser. 3, vol. 5, sect. 4, 1918, p. 63.

[24] Vladykov and Tremblay, Natural. Canad., vol. 62, 1935, p. 80.

[25] Annual Reports, Newfoundland Fisheries Research Commission, vol. 1, No. 4, 1932, p. 108; vol. 2, No. 1, 1933, p. 126; vol. 2, No. 2, 1934, p. 115.

[26] Kendall, Proc. Portland Soc. Nat. Hist., vol. 2, No. 13, 1909, p. 214.

[27] Goode and Bean, Smithsonian Contrib. Knowl., vol. 30, 1895, p. 284.

[28] Abbot, Geology of New Jersey, 1868, p. 816.