MARINE NATURE NOTES

Otago Daily Times, Issue 21918, 1 April 1933, Page 20

MARINE NATURE NOTES

Written for the Otago Daily Times. By David H. Graham, F.Z.S. A RARE FISH. To find North Island fish in Otago waters is not uncommon; to find fish inhabitants of the sub-Arctic islands in these waters is not unknown! but when an Australian denizen pays a visit to the east coast of Otago we begin tq wonder how far fish do wander from their known waters. About a fortnight ago Mr Donald Little, a fisherman of Maclennan, found a fish which was unknown to him or any of the resident fishermen about that part or in the vicinity of Taukuku Beach, where he discovered it washed ashore. It is gratifying to know that he took sufficient interest in the matter to rail the fish to Port Chalmers, where after a good deal of speculation as to its identification, and its transport from one place to another, Mr Reginald Tonkinson, knowing I would be interested, at last placed it in his freezer until my return from the North Island. The fish was dead when found, and the delay did not improve its preservation. It is unfortunate that so many specimens arrive in such condition. It would greatly assist fishery research, and myself also, if those who wish to have anything identified, could forward it direct to my private address, which is 718 King street, when the information wanted will be supplied. This beautifully-shaped fish is known m Australia as the frigate mackerel. It belongs to the same family as the Tunny and Bonito, and is closely related tq the well-known sword fishes. The frigate mackerel is an oceanic fish which appears occasionally in Port Jackson, and, according to the literature available on the subject they do not grow to more than 15 inches. This specimen measures 324 inches over all, and weighed 161 b. On first seeing this frigate mackerel one is struck by the similarity of the animal to that of a submarine. The shape of its body conforms to a number of definite mechanical conditions found in submarines, probably induced by its environment and method of living. It is common knowledge that the mackerel family and the tunny and bonito are one of, if not the fastest fish in the sea. Its outward appearance does not lend itself to actual beauty, but the gracefulness of its spindle-shaped body, every line of its contour, smooth and rounded, give the frigate mackerel an elegance and beauty of its own. One might easily call them typical fish submarines, as they are able to make their way in the sea, in any direction, at almost any angle, with a speed of rapid progression. Though not beautiful in colouring, as compared to bright scarlet vivid coloured fish, they have a colour more beautiful than many other fish. The general colour is lead black, the upper part of the fish above the lateral side line being marked with wavy bands of black and dull greeny some of these wavy streaks form reticulations and enclose small pale spots of the colour of the back. This dark lead colouring gives the fish an elegance which is difficult to describe, not unlike a well black-leaded and polished stove or range. The belly and sides of the fish are silvery white. As man constructed the submarine to allow it to move freely through the water at top speed, so this fish is constructed in order to attain the most efficient movement with the greatest economy of energy. The shape of a frigate mackerel or other allied fish is fusiform; that is, something like a cigar, circular or ellipitical in cross section and thicker in front than behind. The snout is pointed and conical in shape, the body tapers away rapidly towards the shaft of the tail, from which a fairly large forked tail spreads_ out fan-wise. The skin is smooth and slippery, and on a more close examination of the back_ it is seen that Nature again made provision for this fish to attain speed. There is a distinct groove on its back which is sufficiently deep to allow the dorsal,, fin to he right down out of sight and thus offer no resistance to the water. Even the second dorsal and underneath fins > arc partly sheathed and so arranged to give the least resistance to the water. Further, it is noticed that the side (pectoral) and ventral fins also fit into somewhat shallow depressions in the body of the fish. It is thus seen that when this fish is travelling at a high rate of speed a clean, smooth surface is presented, thus allowing it to literally glide through the water. There is no distinct neck in fish as in land animals. The jaws, too, fit so closely together that it is scarcely possible to insert a knife blade between them. Even the eyes are so constructeed as to eliminate any resistance to water. The eyes of fish they have no lids, but many forms in the bony fishes have a gelatine-like covering over the eye, and in the mackerel family it extends almost entirely over the eyeball, leaving only a narrow slit in front of the pupil.’ These firm, smooth eyes carefully adjusted so that their surfaces are level with the other parts of the head may definitely be said to be of service to these swiftly moving fish in presenting a smooth surface to the water._ Further, the minute scales on the skin of the frigate mackerel offer practically no resistance to the forward movement. This is further made possible by a copious supply of slime from the body of_ the fish, which must therefore reduce friction with the water to a minimum. When a fast-moving fish is speeding through the water there must be considerable displacement of water by the forward motion, and it is in the shape of the fish, i.e., smooth, hollow curves of the hinder end of the body extending from that part of the back to the tail, that permits of the passage of the water displaced during the rapid forward motion. Between the second back fin and the tail are a number of finlets which are of great material assistance to the fish when speeding by, giving stability when the large back fin is lying in its groove, ihey act as so many small rudders, and on account of their smallness and position towards the tail offer no resistance to the water. . . Several of those who saw this fish could not understand why it should be so decidedly dark in colour on the upper halt and silvery-white below. The colours, patterns, and shadings exhibited by different fish have given the naturalist much toocl for thought. The colouration of fish may bo for two reasons, either for escape from their enemies or for pursuit of their prey—to conceal them from their enemies or to conceal them from their prey, hish such as the frigate mackerel inhabiting the surface of the sea are coloured black or dark green above and silvery white below.v The sea water is as a rule blue or green, and the frigate mackerel with its dark black and green wavy bands is inconspicuous when seen from above against a background of dark water, while from below the silvery white is inconspicuous against a white sky, and as this fish is more often the pursuer than the pursued, its colouration enables it to approach its prey without being conspicuous. The colouration of fish is most interesting, and we know that the black colours on the back are produced by the crowding together of the black chromatophores (pigment cells), this reducing or eliminating the number of yellow or lighter coloured pigment cells; while the green bands are produced by an equal blending of yellow and black pigment cells. -^. n regard to the colouring on the belly, this is caused by the absence or disappearance of the chromatophores and the greater amount of opacity of the_ skin reflecting tissue layer of iridocytes (iridescent cells) sometimes known as guanin granules, of which the skin of fish is composed, ibis colouration thus enables the frigate mackerel to secure its prey while sliding through the water at top speed. Just how the name "frigate was given to this mackerel I am unable to say definitely, but is probably given from the fact that a frigate vessel is one used for cruising and typical of this fish. Or it may be that as English sailors gave the name frigalte to swift flying birds they may also have likened this mackerel to those birds. No other species of fish can show a finer proportion in the shape .of its body than the frigate mackerel. Every part is adapted for water progression; even the muscles along the backbone are greatly developed. This is more so in that part near the tail, which gives the fish a certain rigidity. The flesh is the firmer on this account; the muscles of the several segments are interlaced and are said to receive a greater supply of blood vessels and nerves than is found in other species of fish. The flesh is of a red colour and the greater muscular energy is said to raise the temperature of the blood of this fish several degrees higher than in other fishes.