A Freshwater Smelt from Lake Rotorua.

By G. Stokell.

[Read before the Canterbury Branch, October 7, 1942; received by the Editor, July 28, 1943; issued separately, December, 1943.]

In a recent paper (Stokell, 1941, pp. 365 and 367) the present writer noted the occurrence in Lake Rotorua of a smelt which differed structurally from other forms, but did not feel justified in defining a species on the very small specimens then available. Through the kindness of Mr A. Kean, Conservator of Fish and Game, a good series of adults was received later, and has been utilised in the preparation of the present description. There appears to be no doubt that this fish is lake-dwelling, although its affinities are more with the estuarine species R. retropinna Richardson than with R. obtusirostris Stokell, which is the only fresh-water species so far recorded from New Zealand.

The material examined during the preparation of the present paper was collected on December 4, 1941, and included small, immature specimens which appeared to have been existing in close association with the adults. The latter were almost ripe for spawning, but differed from estuarine species taken at the same stage of development in having a considerable quantity of food in their stomachs. The parasite Hedruris spinigera, which occurs in a large percentage of the adults of all estuarine species, was absent. Mr Kean informs the writer that in 1930 smelts were present in Lakes Rotorua, Rotoiti, Rotoehu, Rotoma, and Okataina, but could not be discovered in the Blue and Green Lakes, Tarawera, Okareka, Okaro, and Taupo, in all of which they have since been established.

Retropinna lacustris n. sp.

B. 5. D. i-ii 8–11. A. ii-iii 15–16. P. i 10. V.6. C. i 1 6 i (developed rays) Vertebrae 52–54.

Head 4.14–4.29 in. standard length, profile of snout almost straight, jaws about equal or the lower slightly protruding. Maxillary reaching about to middle of eye, moderately dilated posteriorly, may be toothless or with 1–4 teeth. Premaxillary underlying rather more than anterior third of maxillary, toothed. Teeth on head of vomer larger than those on premaxillary, 4–5 in a single row, separated from palatine teeth by a moderate gap. Palatine teeth uniserial or irregularly biserial, teeth on entopterygoids variable from a single row to a scattered patch about four wide, mandi-bular teeth uniserial throughout, biserial anteriorly or irregularly disposed in a narrow band. Lingual teeth largest of all. in two rows with 3–5 somewhat smaller teeth at base of tongue, hyoid with a long patch of comparatively large teeth.

Dorsal fin inserted at 63–65 of the standard length, pectoral extending 53–73 of the distance from its root to the ventral, ventral inserted at 47–48 of the standard length, extending 50–73 of the distance from its root to origin of anal, 56–59 cross rows of scales from upper angle of gill opening to hypural joint. Keel variable, usually becoming prominent somewhat before the tips of the ventrals. Stomach almost tubular when empty.

Maximum total length observed 60 mm.

The species is named on account of its lake-dwelling habit.

Holotype in Canterbury Museum.

Type locality: Ohau channel, near Lake Rotorua.

Differs from R. retropinna in having less vertebrae, a longer head and in the form of the keel; from R. obtusirostris in having less vertebrae, less convexity of the profile of the snout, a more posterior ventral insertion, the variability of the mandibular dentition and the form of the keel.

Literature Cited

Stokell, G. 1941. A Revision of the Genus Retropinna. Rec. Cant. Mus., Vol. 4, No. 7, pp. 361–372.