Art. XXVII.—On the Occurrence of the Salmon Trout in Nelson Harbour.
[Read before the Wellington Philosophical Society, 17th September, 1881.]
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|Length of head||5|
|Least depth of tail||2|
|Distance between end of snout and eye||1.2|
|Length of maxillary bone||2|
|Distance between eye and angle of operculum||3|
|Distance between occiput and origin of dorsal fin||7|
|End of dorsal to root of caudal||7.5|
|Length of base of dorsal||2.8|
|Greatest height of dorsal||2|
|Length of pectoral||3.6|
|Boot of pectoral to ventral||7.4|
|Length of ventral||2.5|
|Ventral to anal||5|
|Length of anal||3.3|
|Greatest depth of anal||2.9|
|Length of longest caudal, say||3.2|
|" middle "||1.9|
|Weight, 64 ounces.|
The greatest depth of the body is beneath the middle of the dorsal fin, and is equal to the extreme length of the head and one-fifth of the total length. The snout is conical, but compressed vertically. Mouth terminal, the jaws fitting evenly when shut. Maxillary bone dilated and extending slightly beyond the posterior vertical of the eye. Diameter of the eye is
one-third the length of the snout. Tip of snout to occiput two-fifths the total length of the head measured to the hinder angle of the operculum. The interorbital space is only slightly convex. Opercles are thin, with concentric striæ. The posterior margin of the operculum is almost straight, oblique, the sub-opercular suture being at right-angles, and only slightly sinuated. The sub-opercular is three times as long as broad. The ratio of the length of the fins to the total length is as follows:—The length being 1.00; D. .125; P. .069; V. .100; A. .076; least depth of tail .125. The caudal fin is slightly emarginate. The dentition is complete and powerful, the intermaxillary mandibular and front vomerine teeth being the largest. The maxillary teeth are arranged in pairs. The head of the vomer has a group of three teeth, and three on each side of the body. The tongue is armed with teeth arranged in the same manner and number as on the vomer.
There are 120 perforated scales on the lateral line, which is prominent. From the front origin of the dorsal to the lateral line there are 26 scales, and from between the origin of the ventral and the lateral line there are eighteen rows of scales. The scales are thin and rounded in posterior outline. Immersed nacreous scales occur along the back from the nape to beyond the dorsal.
The snout and muzzle are olivaceous black. The crown and occiput honey yellow. On the cheek and above the eye is a triangular patch of brown. The gill-covers are silvery white with a dusky hue, and have five dark spots, four on the operculum, and one on the pre-operculum. The under parts as far as the vent are pure white.
The nape and back dark blue-black, and the flanks bright silvery with a purple shade. Diffuse and X-shaped black spots on the back and sides, but only a few below the lateral line. Dorsal fin dusky brown with numerous dark spots. Pectoral darkened toward the tip on the inner side. Ventrals and anal white. Adipose and caudal dark coloured.
The fish which is now exhibited was sent to me yesterday by Mr. Greenfield, Secretary to the Acclimatization Society, Nelson, as being, probably, a specimen of the Californian salmon (Salmo quinnat). It was captured in Nelson Harbour, near to the mouth of the Maitai Stream, a similar, but smaller, specimen of the same fish having been caught there a few days previously.
Californian salmon having been turned out, three years ago, in various rivers entering Cook Straits and in the Nelson District, while no other migratory salmonoid had ever been liberated, so far as is known, north of Otago, it was not unnatural to suppose that this might be a harbinger of the shoals of American salmon that are expected sometime to reappear on our coasts.
A careful examination of the fish shows, however, that it must be classed as a true sea or salmon trout, although, as has been found invariably to be the case in Otago specimens, it presents a certain admixture of the characters of the many species into which the sea trouts from the various rivers in Europe have been subdivided.
The specimen proves to be a female that has just spawned. For the length of twenty-five inches its weight, four pounds, is small, but it is evidently lanky and out of condition, as otherwise it would have been a six pound fish. The stomach contained half-digested remains of a young barracouta (Thyrsites atun) and a sea mullet (Agonostoma forsteri), each about nine inches long, proving that it must have been feeding voraciously in salt water. The importance of this determination is due to the fact that the only salmon trout ever introduced to New Zealand were bred from a small lot of ova that came from Tasmania, in 1870, and of which the original stock, turned out in Shag River, Otago, did not exceed seventy or eighty fish. What are supposed to be the progeny of these now abound on the Otago coast, and this discovery might seem to point to its having spread in its migration round the coast as far as Blind Bay. On the other hand, it might be suggested that what we know as brown trout in the rivers are of the large fast-growing variety known as the Thames trout, but which, in New Zealand, enter the sea and acquire the characters of the true sea trout.