MARINE NATURE NOTES

Otago Daily Times, Issue 23203, 29 May 1937, Page 21

MARINE NATURE NOTES

Written for the Otago Daily Times Bv David H. Graham. F.R.M.S., F.Z.S. THE LAZIEST FISH IN THE WORLD About two years ago Miss K. Fraser, of Dunedin, asked for an article on the remora or sucker-fish, ! and Miss E. M. Baldock, of Inverj cargill, has asked for some informaI tion as to its habits. I know of no | better name than " lazy fish " for this fish unless it be the " swordfish's j attache," as it is more often found attached to the swordfish than any other fish. The remora is one of the queerest fish in New Zealand and perhaps in the whole ocean. Others may have a more extraordinary—or, at any rate, a more terrifying—appearance, but not one of them is constructed on such an original principle, or has such a quaint and ingenious method of getting through the world with least trouble. The remora is distinguished from all other fishes by the fact that the spiny part of the back fin is modified into a flat, oval sucking plate composed of a double series of cartilaginous crossplates with serrated edges situated on the top of the head and neck. All remoras are slender of form, with the lower jaw projecting far beyond the upper. Their large mouths are armed with many small, pointed teeth; the lower surface of the head is convex; the upper, flat—just the reverse of the usual rule—with the lower surface of the body as deeply coloured as the upper, the back often being mistaken for the belly. The only specimen seen by the writer was taken from a swordfish at the Bay of Islands, and measured four inches in length. Its colour, which is constant with this species, is light reddish brown above and darker below, with paler back and anal fins. The swordfish sucker lacks the side stripes and white fin edgings so characteristic of the shark sucker. The swordfish sucker's habitat is that of warm seas generally, paralleling that of the swordfish. One question asked by the correspondent from Invercargill is, "Is it a fact that all swordfish carry a sucker-flsh? " My information from swordflshermen and from other sources is to the effect sometimes several suckers are fastened to a single swordfish, but far more swordfish are seen lacking than carrying those uninvited guests. Nothing except the bare facts just mentioned is known of the habits of the swordfish sucker. Presumably it feeds on fragments of the fish killed by its host; presumably, too, it is as active a swimmer as its host. Nothing whatever is known of its breeding habits. Although quite a strong swimmer and well able to forage for itself, the remora prefers to cling to the skin of other animals to be whisked about without any effort to itself, lunching off the bits that its host overlooks. From a sociological point of view, the study of the remora is full of intense interest. Here we have a fish that to all outward appearance is fully equipped for the, battle of life in the sea. In no way handicapped by weakness, it has deliberately chosen to live upon the energies of others, and to expend the minimum amount of effort to obtain the necessary sustenance which is necessary for its support. The top of its head is flat and oval in plan, while upon it is formed a strangely conventional apparatus which makes an efficient sucker, though it looks more like a piece of regularly designed grating, or the sole of a tennis-shoe, or perhaps like a Venetian blind in miniature. Not only are all its organs perfectly normal, but it is rather better equipped for swimming than many fish. When a sucker-fish attaches itself to a swordfish, shark or other large fish, it depresses the base of its disc by so doing creates a partial vacuum which forms an extremely powerful attachment. Whatever this disc touches it adheres to with the

greatest tenacity. The reason is that the air between the plate and anything it lies against is forced out j (exactly like the small boy's leather j sucker), so that a vacuum is created, and when once this is the case the two things that touch each other always stick together. It is on this principle that a fly is able to walk along the ceiling, for all its six feet end in so many little adhesive discs or suckers, which act as strongly, in proportion to their size, as does that of the remora. The arrangement of the sucking disc is such that the fish can free itself without effort by swimming forward, but if an attempt is made to remove it by pulling it from behind, so secure is the adhesion that the flesh of the host is likely to tear apart before the disc is detached. It seems probable, indeed, that when pulled backwards the remora is unable to let go. The peculiar mode of life of the remora and the structural adaptation associated with it probably' arose from the habit found in many fishes of accompanying larger creatures either for protection or gain, and of concealing themselves under the shelter of any large object in the sea. This habit of pushing close up against the larger creatures has in the course of time—probably thousands or millions of yearscaused the dorsal fin to become developed into the sucking disc in a manner similar to the ventral fins of the rock-sucking fish so abundant round our shores. This rock-sucker fish has, in the course of time, so used its under surface to lie flat against the flat rocks that the anal fins have in time also become. a sucker.

Of all the sea fish, the remora must have the easiest, laziest and safest time of them all. To all but the remora the fierce and greedy monsters of the deep, the shark, the swordflsh and the killers, are a terror and a menace; but what can any of them do to a small fish which clings close to the under surface of its host? Of all the places in which this lazy fish loves to lurk, there is none so greatly to its mind as the roof of the mouth of some large shark. Here, with its head pointing in the direction in which its host is going, it can and does take toll of all the food that enters, and, as it is omnivorous, nothing ever comes amiss to its palate. It is able to perform all the natural functions while in this position'; and so it reaches at once the summit of its ambition, that of obtaining its needs with the minimum of effort.