Art. IX.—On Exocœtus ilma: a New Species of Flying-fish.
[Read before the Wellington Philosophical Society, 14th March, 1899.]
It is not without due consideration and careful watching of this species for a long period that I have the honour of introducing it to your notice. The first specimen I obtained carries memory back to a universally known figure in the New Zealand Union Steamship Company's service, some few years ago entombed in a watery grave—I allude to the late Captain John McIntosh. Whilst on a voyage from the west coast of the South Island to Sydney in May, 1882, in the s.s. “Alhambfa,” having gained an offing of eighty to a hundred miles from the land we left the previous evening, I was on deck at sunrise, it being a beautiful clear morning, with but the lightest breeze and a long, low, lazy swell. Whilst walking up and down the deck with the above-mentioned officer a small flight of flying-fish arose from the sea, and passed, with one exception, over the vessel, rising above the awning then stretched over the quarter-deck. The exception came on board between the rail and the awning, falling almost at our feet. “A happy omen, Clarke,” the captain exclaimed, “you shall have it cooked for your breakfast.” I picked it up, and, after examining it, replied, “No, captain, I think it is a new variety from the great length of its fins; I will embalm it in some of the steward's best gin or whisky pro tem., and devote its body to a more scientific fate.”
Since that date several of the same kind were washed ashore on the coast of Westland, whilst one was caught on a light line by Mr. Harry Breeze, of Hokitika, when fishing for Agonostoma (“aua,” so-called herring or-sea-mullet) from the beach. Several of these were carefully examined and compared by me with my original drawing and notes, and exhibited the same characters as my type specimen, and all, strange to say, were about the same size. It has also come under my observation on shore, once on the coast of Taranaki; and twice whilst on the sea, when fishing from or paddling in a Rob Roy canoe, flying-fish, which arose from the water close by the canoe, had apparently the same large black type of pectorals. It may be useful to record that several times since my residence here flying-fish have been reported to me as having been seen off the end of our breakwater.
Dr. Günther, in his “Study of Fishes,” says the flying-fish “are more frequently observed in rough weather and in a disturbed sea than during calm.” And also he agrees with what is usually published, that “the fins are kept quietly distended, without any motion, except an occasional vibration caused by the air whenever the surface of the wing is parallel with the current of the wind”; also, that “in the day-time they avoid a ship, flying away from it.” My experience of these fishes differs from these remarks, and my inquiries for years amongst “sailor-men” have generally substantiated this where their observation has been evidently carefully directed to them. Of course, it can be understood from the varying development of the pectoral and ventral fins in the numerous species that some differences of flight habits must occur; those in which the pectorals and ventrals are much less in comparison with the size of the body may safely be accredited with less powers of direct progression through the air, and probably an incapacity for turning or wheeling in flight at all. And these generally are the characteristics of the Atlantic species.
The result of my observations and inquiries is that more are observed in calm weather or light breezes; that swerving or wheeling in flight is fully within the capacity of most of those species frequenting the Indian Ocean, the seas of the Malay Archipelago, the China seas, and the equatorial and South Pacific towards the coast of New Zealand and in the Tasman Sea; that they frequently resort to the presence of a large boat or ship for protective shelter from their enemies, as is evidenced from such habit being taken advantage of by the fishermen, who capture them when so doing—vide the accounts of the flying-fish harvest off the shores of the Bermudas, &c.—and from the low-waisted native traders along the Indian coasts being easily able to attract them aboard by the exhibition of lights for such purpose at night; that they in daylight come aboard in about the same ratio as at nighttime, when no attractive special display of lights is made; that a continuous vibrating movement is given to the pectorals in aerial flight. I have been, myself, in such a favourable position when the fish have arisen from the sea that a vibratory hum has been audible—almost the same kind of clashing noise as is noticeable in the flight of the larger dragon-flies. Those which came on board vessels in which I have been travelling did so in the day-time. One flew through a port-hole—in the old “City of Hobart”—and dropped into a hand-basin, after striking against the body of my sister, who was washing her hands and face therein. No doubt they would avoid a ship as much as possible, and perhaps do, unless under the circumstances previously quoted, which
are exemplified by several other varieties of fishes; but the vessels' disturbance of them in the water, especially if a steamboat, is frequently, I think, a cause of their misdirection of flight.
Third division, ventral fins long, extending beyond posterior termination of base of anal.
Exocœtus ilma, sp. nov.
D., 12; P., 16; V., 6; A., 12; C. (7 upper limb, 8 lower limb), 15.
B., 8. L.L., 28 scales to origin of ventrals; 25 from same to termination of line which finishes before caudal is reached; 29 scales between occiput and origin of dorsal; and 6 longitudinal series of scales between origin of dorsal, and lateral line. (This is common also with three other species of Exocœtus.) Speculiger also has same number, occiput to origin of dorsal, but according to Günther 6 to 7 between each point and lateral line.
Height of body is contained six and seven-tenths times in the total length (without caudal)—viz., if such length is reckoned along the median line from tip of snout to termination of the fish at the base of the central caudal rays—but if such height is compared with the total distance from snout to the vertical of origin of rudimentary rays of caudal, then it is contained in the latter six and a quarter times. This height of body is greatest and equal in that space between the verticals from a little posterior to the origin of pectorals and at the origin of ventrals.
Günther's description of speculiger gives one-sixth or nearly one-seventh of the total length (without caudal) as the proportion of depth, and in nigripinnis one-sixth or a little less than one-sixth total length (without caudal). Four other species in this division of Exocœtus are described with the same proportion as one-sixth, and four of it as a sixth and a half, which broadly means that about such a proportion appertains to the Exocœti with long ventral fins.
The length of the head is contained five and a half times in the total length (without caudal) first defined—i.e., a proportion of two-elevenths. Günther's descriptions of speculiger and nigripinnis give head as two-ninths. The snout is very obtuse and short; on Plate VI. its peculiarities are reproduced. In its profile it is abrupt; the lower jaw projects beyond the upper when mouth is closed; therefore the chin forms the
most prominent portion of the tip. The lower jaw is also the longer when the mouth is fully open, and the jaws have some slight capacity of protrusion. The month is very small. A few very minute, short, thick, recurved teeth in a doable row at the tip of the lower jaw and a single row of the same description around the centre third of the upper jaw. There is a small, round, hard nodule at that posterior higher angle of the preorbital immediately adjoining the margin of orbit. The length of snout from anterior margin of eye, with mouth closed, exactly equals half the diameter of the eye. (In speculiger the snout is rather produced, and very nearly equals the diameter of the eye.) The eye, as compared with the size of the head, is very large, its diameter being contained twice and a little more than a half in the length of the head. (The eye of speculiger is one-third the length of head, that of nigripinnis two-fifths.) The interorbital space in a line even with the anterior margins of eyes exceeds the diameter of the eye, and in even line with posterior margins of eyes exceeds diameter of eye by one semi-diameter. This space is almost flat, being but slightly depressed in median line, the profile of such depression slightly convex, as are the supraorbital spaces. The top of the head at the interorbital space and to the occiput is free from scales, bony, and hard. The depth of head (under the vertical from occiput) equals the distance between the tip of snout and vertical falling through the posterior margin of preoperculum. The body is thick and robust, the back—which, with the top of the head, is slightly flattened—being much the wider. Sides and cheeks are also flattened, but incline towards the ventral edge, the lower part of the body being thus narrower and more angular, especially under the head and throat, though still stoutish.
[The section below cannot be correctly rendered as it contains complex formatting. See the image of the page for a more accurate rendering.]
The pectoral fins are wide and long, extending, when closed, to considerably beyond the commencement of the rudimentary rays of the caudal fin. Ventral fins commence exactly midway between verticals of posterior margin of eye and “root of tail.” They also are long and broad, and extend, when laid back, almost to midway between the terminal line of anal and commencement of rudimentary rays of caudal. The two external rays of caudal fin adjoining the rudimentary rays are quite stout. The dorsal commences a little in advance of the plane of anal, but terminates exactly in same plane as anal. The scales are large, the larger averaging quite 3/10 in. in width when detached from their sacs. Attached they have so great an overlap as to make them appear much smaller. The series forming the lateral line are much smaller, each being provided with tubular mucous duct. They are arranged directly on the epidermis; the general scales both above and below partially overlap them. The eyes are provided
with the external transparent membranes or eyelids, with vertical oval aperture, so frequently met with in many of the pelagic surface or medium-depth fishes.
Colour: The top of the head and back brownish-purple; cheeks, sides, and part of the belly silvery, with golden reflections; the lower part of the belly pure white. The exterior surface of the pectorals when closed are covered with a silvery integument almost up to its tip, this being caused by the external portions of the rays being so covered; when spread the intervening membrane is very dark-brown. The whole of the interior surface of the pectorals” is uniformly a very dark brown, almost black. Ventral fins uniform dark-brown, almost black. Dorsal and anal fins immaculate. Upper and lower limbs of caudal brown, central portion immaculate.
The pectoral fins of speculiger have “an oblique white band across its lower half” and “a broad whitish edge,” whilst its “ventrals are white, the middle rays greyish.”
|Total length (snout to “root of tail” end of body, along median line thereof at caudal)||7.7|
|Length of head||1.4|
|Greatest depth of body||1.15|
|Greatest diameter of eye||0.55|
|Greatest height of dorsal||0.7|
|Greatest height of anal||0.65|
|Length of dorsal||1.22|
|Length of anal||1.15|
|Greatest length of pectorals||5.7|
|Greatest length of ventrals||2.55|
|Distance from anterior margin of orbit to tip of snout (end of chin)||0.275|
|Length of lower limb of caudal||2.2|
|Length of upper limb of caudal||1.6|