Fig. 51.—Bluefin Cisco, Argyrosomus nigripinnis Gill. Sheboygan.
Closely allied to the lake herring is the bluefin of Lake Michigan and of certain lakes in New York (Argyrosomus nigripinnis), a fine large species inhabiting deep waters, and recognizable by the blue-black color of its lower fins. In the lakes of central New York are found two other species, the so-called lake smelt (Argyrosomus osmeriformis) and the long-jaw (Argyrosomus prognathus). Argyrosomus lucidus is abundant in Great Bear Lake. In Alaska and Siberia are still other species of the cisco type (Argyrosomus laurettæ, A. pusillus, A. alascanus); and in Europe very similar species are the Scotch vendace (Argyrosomus vandesius) and the Scandinavian Lok-Sild (lake herring), as well as others less perfectly known.
The Tullibee, or "mongrel whitefish" (Argyrosomus tullibee), has a deep body, like the shad, with the large mouth of the ciscoes. It is found in the Great Lake region and northward, and very little is known of its habits. A similar species (Argyrosomus cyprinoides) is recorded from Siberia—a region which is peculiarly suited for the growth of the Coregoni, but in which the species have never received much study.
Brachymystax and Stenodus, the Inconnus.—Another little-known form, intermediate between the whitefish and the salmon, is Brachymystax lenock, a large fish of the mountain streams of Siberia. Only the skins brought home by Pallas a century ago are yet known. According to Pallas, it sometimes reaches a weight of eighty pounds.
Fig. 52.—Inconnu, Stenodus mackenziei (Richardson). Nulato, Alaska.
Still another genus, intermediate between the whitefish and the salmon, is Stenodus, distinguished by its elongate body, feeble teeth, and projecting lower jaw. The Inconnu, or Mackenzie River salmon, known on the Yukon as "charr" (Stenodus mackenziei), belongs to this genus. It reaches a weight of twenty pounds or more, and in the far north is a food-fish of good quality. It runs in the Yukon as far as White Horse Rapids. Not much is recorded of its habits, and few specimens exist in museums. A species of Stenodus called Stenodus leucichthys inhabits the Volga, Obi, Lena, and other northern rivers; but as yet little is definitely known of the species.
Oncorhynchus, the Quinnat Salmon.—The genus Oncorhynchus contains the salmon of the Pacific. They are in fact, as well as in name, the king salmon. The genus is closely related to Salmo, with which it agrees in general as to the structure of its vomer, and from which it differs in the increased number of anal rays, branchiostegals, pyloric cœca, and gill-rakers. The character most convenient for distinguishing Oncorhynchus, young or old, from all the species of Salmo, is the number of developed rays in the anal fin. These in Oncorhynchus are thirteen to twenty, in Salmo nine to twelve.
The species of Oncorhynchus have long been known as anadromous salmon, confined to the North Pacific. The species were first made known nearly one hundred and fifty years ago by that most exact of early observers, Steller, who, almost simultaneously with Krascheninnikov, another early investigator, described and distinguished them with perfect accuracy under their Russian vernacular names. These Russian names were, in 1792, adopted by Walbaum as specific names in giving to these animals a scientific nomenclature. Five species of Oncorhynchus are well known on both shores of the North Pacific, besides one other in Japan. These have been greatly misunderstood by early observers on account of the extraordinary changes due to differences in surroundings, in sex, and in age, and in conditions connected with the process of reproduction.