Art. XXVII—Notes on the Anatomy of the Kanae. (Mugil, sp.)
[Read before the Wellington Philosophical Society, 14th October, 1871.]
On the 29th December, 1870, when on a professional visit to the Maoris residing on the shores of Porirua Bay, I accidentally procured a fish which I had not seen previously in that locality. Three specimens had just been captured in a powerful net by Major Edwards, and he kindly put one at my disposal.
The general colouring of the fish resembled, at first sight, that of a salmon just landed; there was no apparent lateral line, but the body was divided by the dorsal segment, presenting a greenish shade, passing gradually to a silvery white on the abdominal surface; the dorsal, pectoral, and caudal fins, partook of the greenish shade, whilst the ventral (pelvic) and anal fins were of a silvery white. The scales, measuring when detached .5 inch by .33 inch adhered firmly to the skin. The eyes were surrounded by a complete circle of a semicartilaginous tissue, adhering to the margin of the orbit, not moveable, and consequently in no way resembling eyelids.
The anatomical examination of this fish presented many interesting features, being altogether new to me.
The stomach was remarkable, not only in shape, but in its organization. When first removed from the body it presented a firm solid mass, and upon being divided longitudinally it was found full to distention of a greenish, earthy looking, pasty substance, which, upon being turned out, continued to retain the shape of the stomach. The pyloric extremity was composed of a powerful mass of muscular fibres, resembling the gizzard of a bird, and about its centre measured one inch in thickness. The intestines were of extreme delicacy. The pancreatic cæca, two in number, were distended with a brownish mucous. Liver weighed 320 grains, and was composed of numerous lobes. Gall bladder free, 1 inch in length, filled with a bright green bile. Spleen weighed 60 grains, was 1.25 inches in length, resembling a clot of blood in colour.
Milt, 4 inches in length by 1 inch in breadth, weighed 320 grains; the artery supplying it and the blood-vessels, more especially near the cloaca, were enlarged, indicating that the organ was in an active state previous to the spawning season.
The muscular system presented an appearance not unlike the curd of milk, or what I used to know as French-white colour. I obtained from the specimen one and a half pounds (avoirdupois) of muscle, free from bone, and
had it placed upon the gridiron forthwith. Having many times partaken of the finest kinds of the salmon, cooked in the most approved style, I hesitate not to say that this fish was infinitely superior in delicacy, richness, and flavour, to that of the Salmo salar.
The dentition in the Mugil family exhibits a striking instance of the direct connection it has with the structoral type of stomach, and the kind of food the animal lives upon. Indeed, the fish may be said to be toothless, a series of almost microscopic ciliæ supported upon the lip surrounding the mouth, and a small patch on the palate bones, constituting the entire system of dentition.
The gills, having four arches, are fully developed, consisting of the usual branchiæ, closely placed, and of great length, measuring, about the centre of the arches, one inch in length, and occupying, as usual, the external or convex margin of branchial arches, whilst the inner or concave margin supports a series of laminæ of extreme delicacy, placed transversely to the axis of the arch, and forming, no doubt, a filter of the most artistic description. *
The pharyngeal bones differ entirely from those of most other fishes. The lower (two in number) are delicate, and may be viewed as a modification of the branchial arch, being covered internally with similar laminæ. The upper pharyngeal bones (two in number) are of an irregular cone shape, one side of the cone rounded and covered with exceedingly minute ciliæ. This part evidently corresponding to, and in certain actions of the throat will be in contact with, the concave aspect of the lower pharyngeal bones.
The entire apparatus is saturated with a fine oil, and the action of this remarkable structure it is difficult to suggest, more especially when we have ascertained the nature of the food.
In the carnivorous fishes, as in the Sparoidœs, Cuvier, (such as the Snapper, Pagrus unicolor) the teeth present nearly every variety of shape or form for holding, tearing, and crushing, notwithstanding which they swallow the fry of other fishes entire, so that the stomach has to select and reject, and thus the intestines are generally loaded with debris of bones, fins, etc.
In the Sciœnadœ, as, for instance, the Moki (Latris ciliaris), a row of minute teeth are placed on the margin of the inter-maxillary bones and lower jaw, whilst the branchial arches and pharyngeal bones present a most complex, and, at the same time, beautiful system of dove-tailing, and a variety of teeth in shape and form. Those in the pharyngeal bones are mostly rounded, blunted, cones. The food of the Moki I have found to consist of the testacean mollusca,
[Footnote] * “The fishes of this genus feed on organic substances which are mixed up with the sand or mud; a considerable indigestible portion of the latter is swallowed; and in order to prevent larger bodies from passing into the stomach, or substances from passing through the gill-openings, these fishes have the organs of the pharynx modified into a filtering apparatus.”—Dr. Günther's “Catalogue of Fishes,” Vol. III., p. 410.
more especially the Mutton fish or Pawa (Haliotis iris), of which, if of large dimensions, the shell is crushed, if small swallowed entire.
Having, when treating of the stomach, alluded to the food, I now resume the subject. Whilst engaged, many years ago, in investigating the natural history of the Estuary Trout, Salmon, Char, Trout, Vendace, and Herring, and more especially the Vendace, the food when found in the stomach presented the appearance of a dry pasty earth. The remarkable delicacy of the fish as an article of food appeared to me difficult to understand, and being at that time in the constant habit of examining all doubtful tissues or substances under the microscope, this earth turned out to be entirely composed of Entomostraca, and microscopic testacea.
I acccordingly subjected the sand or mud found in the stomach of the Kanae to the searching properties of a drop of fresh water and a compound microscope, and could distinctly trace various organic forms, which, however, I failed to identify. I thereupon availed myself of the assistance of Mr. Buchanan and his microscope, and give the result in his own words, and beautiful sketches of these forms, which proved to be chiefly Diatoms:— “I received your small packet, and, at your desire, have examined the contents under the microscope. You gave me no instructions what to look for in the earthy matter sent, so I can only report what I made out. It is richer in Diatoms than any earth I have seen. I send you sketches of six species, hurriedly done from a small quantity, without, I believe, exhausting the number. There is nothing besides but silicious grains and mud.”
The skeleton, I may remark, presents the peculiarity observable in that of most fishes prized for their richness and superiority as an article of food. The bones of the Salmon, Estuary Trout, Char, etc., can by no process of bleaching be made white. A rich oil penetrates into every tissue, even that of the elementary cartilages of the skeleton and the bones themselves.
Weight, recent, 31bs. 9ozs.; weight of skeleton, 2oz. 246grs.; and of soft parts, 31bs. 6ozs. 234grs. Twenty-four vertebræ; twelfth the largest, .42 inch in length, diminishing very slightly towards the tail. Nine pairs of ribs; fourth the largest, 2.25 inches in length. The specimen dissected presented the abnormal character of having five instead of four spines in the first dorsal fin, which is a departure from the family character of the Mugilidœ.