The Occurrence of Hyoidal Teeth in Salvelinus fontinalis.

Transactions and Proceedings of the Royal Society of New Zealand, Volume 70, 1940-41, Page 161

The Occurrence of Hyoidal Teeth in Salvelinus fontinalis. By G. Stokell. [Read before the Canterbury Branch, December 6, 1939; received by the Editor, May 21, 1940; issued separately, September, 1940.] A Large char (Salvelinus fontinalis) taken at Lake Emily in the Ashburton Valley and forwarded to the Canterbury Museum in March, 1939, was found to differ from the general conception of this species in having teeth on the hyoid bone. Jordan (1925) writing of Salvelinus fontinalis states: “There are no teeth on the hyoid bone, traces at least of such teeth being found in nearly all other species.” Gunther (1866) records of this fish: “No median series of teeth along the hyoid bone.” Regan (1914), who suggested some alterations in the classification of the Salmonidae, proposed the union of the chars into a single genus which, he suggested, should be divided into three groups as follows:— (1) alpinus group. Head of vomer with posterior process but little developed. Basi-branchial teeth uniserial. (2) fontinalis group. Head of vomer with a well-developed posterior process. Basi-branchial teeth absent. (3) namaycush group. Head of vomer with a long posterior process. Basi-branchial teeth in a long patch. In the face of these definite assertions of the absence of hyoidal teeth in Salvelinus fontinalis, the identity of the Lake Emily specimen seemed open to question, particularly as the fish was obviously of lacustrine habit and weighed about 4 ½ lb., a weight seldom associated with this species. The same dental characters have, however, been observed in a considerable percentage of small, river-dwelling char from Canterbury streams. Of 17 specimens in the writer's collection, 6 have from 1 to 7 hyoidal teeth visible without dissection, 3 show more or less rudimentary teeth when the bone is laid bare, and the remaining 8 show no definite trace of hyoidal teeth, the different arrangements occurring indiscriminately in specimens of all ages. Fig. 2 shows the side view of the hyoid and tongue of a specimen having maximum development of teeth. It was also found that the specimen of Salvelinus fontinalis in the reference collection of American Salmonoids in the Canterbury Museum, which was determined and forwarded by the American Bureau of Fisheries, has one tooth visible on the hyoid. In all of these specimens the head of the vomer carries teeth arranged in the form of an obtuse V, the body of the vomer being toothless, much

elevated above the level of its head, slightly arched longitudinally, and of an inverted V shape transversely. A photograph of this bone viewed laterally is shown in fig. 1. All specimens have the large mouth and long maxillary typical of fontinalis, and show the vermiculated markings on the back which are indicated by Jordan and Evermann (1896) as being restricted to this species. As the specimens in which no hyoidal teeth exist come well within the accepted definition of fontinalis it is not possible, in view of the complete intergradation between them and the specimens possessing a complete row, to regard extreme forms as distinct, particularly as no association with differences in other characters is evident. It is therefore necessary to re-define Salvelinus fontinalis as being variable in the occurrence and number of hyoidal teeth. A description based on the examination of ten Canterbury specimens including all types of dental variants is appended, together with a photograph (fig. 3) of a typical example. The Lake Emily fish differed from this specification in having a comparatively shorter pectoral fin and in the more forward position of the ventrals, these being inserted at ·46 of the standard length, and exactly opposite the dorsal. The writer wishes to express his thanks to Dr. Falla, of the Canterbury Museum, for access to the specimens mentioned, and to Dr. Dymond, of the Royal Ontario Museum of Zoology for providing literature. Salvelinus fontinalis (Mitchell). B 9–11. D iii–iv 8–10. A ii–iv 8. P 11–13. V 8–9. C 19 (developed rays). Vertebrae 56–58. Head 3·6–4·29 in standard length, eye 4·51–5·16 in head. Mouth very large, maxillary 1·3–1·85 in head, extending far behind posterior of eye. Teeth arranged in a chevron on head of vomer, body of this bone toothless, much elevated above level of its head, somewhat curved longitudinally and of an inverted V shape transversely. Hyoid bone without or with small teeth which may be rudimentary or developed, numbering from 1 to 7, usually arranged in a single series, but in one specimen partly biserial. Gill rakers 14–16, pyloric caeca 26–36. Dorsal fin inserted at ·45–·47 of the standard length, its height usually more, but sometimes slightly less, than its basal length. Pectoral extending ·50–·64 of the distance from its root to the ventral, ventral inserted at ·52–·55 of the standard length, length of axillary contained 3·29–4·18 times in height of ventral. Height of anal much more than its basal length, adipose rather small, caudal obtusely notched. Caudal peduncle 1·4–1·9 times as long as its least depth. Scales rather irregularly aranged, and number of cross rows somewhat indefinite, but usually about 230, the count being made immediately above the lateral line, and continuing to the posterior limit of the scale covering. Only one scale in lateral line to each two cross rows.

Fig. 1.—Vomer of Salvelinus fontinalis. Fig. 2.—Tongue and hyoid of Salvelinus fontinalis. L: Lingual teeth. H: Hyoidal teeth. Fig. 3.—Salvelinus fontinalis, Hinds River, Canterbury. Total length, 10 inches.

Colour: Back, olive with darker vermiculated markings which extend on to the dorsal and caudal fins. Belly, orange or silver according to season, sides dark, with red, yellow and blue spots which extend below the lateral line. Anterior edge of pectorals, ventrals and anal white, a narrow black band following, remaining part usually orange. Mature at total length of 6 inches. Literature cited. Gunther, A., 1866. Cat. Fishes British Museum, v, 6, p. 152. Jordan, D. S., 1925. Fishes, D. Appleton and Co., New York, p. 333. — and Evermann, B. W., 1896. The Fishes of North and Middle America, Bull. U.S. Nat. Mus., no. 47, part 1, p. 506. Regan, C. T., 1914. The Systematic Arrangement of the Fishes of the Family Salmonidae, Ann. Mag. Nat. Hist., series 8, vol. 13, pp. 405–408.