Fish that Catch Fish

Dominion, Volume 26, Issue 30, 29 October 1932, Page 16

Fish that Catch Fish

IF shark-suckers were as plentiful in New Zealand waters as they are in some other places, Maori fishermen, doubtless, would have put the strange discs on the top of these fishes’ heads to practical use, as is done by native fishermen in the tropics. The disc is a singular development of the first fin on the back. It is slightly misnamed, as it is elliptical, not round. It has a rim of flesh. Across it, from side to- side, are slats of tissue, equipped with spines. Mr. E. W. Gudger, an American ichthyologist, who has observed shark-suckers in an aquarium, explains that.a sucker places its disc flat against the flank of a shark or of another large- fish,. By muscular contraction, it raises the rim and the slats, creating a partial vacuum. By the atmospheric pressure, and by the pressure of the water, the shark-sucker holds fast to the larger fish, and is carried about by it. The fine spines on the slats, sticking into the skin of the larger fish, help the shark-sucker to hold on. It might be thought that the shark-sucker is not a swimmer, and that it uses its device in order-to have free trips through the water. The truth is, it can swim quite well, and so swiftly as to catch up with a shark. Its object merely is to share the larger fish’s meals. Most sharks, Mr. Gudger points out, have sharp, pointed teeth, suitable for tearing, or broad, serrated teeth, suitable for chopping. With these teeth they tear or cut their prey into small pieces. Fragments torn off float in the water. A shark-sucker then relaxes the muscles of its disc, lets go, snaps up the fragments, and again fixes itself to its shark, which swims away to seek another meal for itself and for its companion. The shark does not suffer by the relationship. The disc may cause a tickling sensation, but does no harm. A shark-sucker feeds without giving anything in return, but it takes only the crumbs that fall from the rich man’s table. Although it humbles itself, it is not a parasite. This type of association is well known to zoologists. It is called commensalism. This is from the Latin “com,” together, and “mensa,” table, and means living at a common table. It is different from symbiosis, which means living together for mutual advantage, and from inquilinism, in which one creature becomes the tenant of another creature without paying rent in any shape or form; and it is very different from opprobrious parasitism, common in all parts of the vast and diversified animal kingdom.

(By J. Drummond, E.L.S., F.Z.S., for “The Dominion.”)

A shark-sucker sent to me from Auckland was about five inches long. Its disc was an inch and a half long. In 'Cuban waters, shark-suckers are from thirty-one to thirty-five inches long, and their discs are seven inches long. The Cubans and other people in those parts use them fairly extensively as living fish-hooks. A fisherman tics a long cord to the tail of a sharksucker, kept on board. On arrival at the fishing-ground he put the sharksucker into the water. Darting at a fish, it fixes itself to the skin. The usherman paddles after the shark-sucker and pulls it on board with the fish the shark-sucker selected for its attention. “In this way,” Lady Brassey wrote in her yacht, the Sunbeam, “one of the ugliest and most incapable looking creatures is, by savage instinct, made to become of some use in procuring food for a superior animal.” When Lady Brassey, forty-seven years ago, published her account of these fishing operations it was discredited. Later observations confirmed it A few years ago, Dr. C. R. de Sola went out from a Cuban port with a party of fishermen. On a turtle being sighted, the fishermen tossed several shark-suckers into the water in the direction of the turtle. Lines tied to the shark-suckers’ tails ran out quickly. They soon became taut. Vibrations showed that the shark-suckers were fast to the turtle, and the boat was rowed to the turtle, which was taken on board. As soon as it was out of the water the shark-suckers let go. All the time the fishermen talked gently to the shark-suckers, assuring friendship, and telling them that, when they returned home, they would be fed and cared for. Turtles often are taken with shark-suckers fixed to them. Some shark-suckers’seem to prefer sharks, this practice giving a name to the group, but manatees, porpoises and almost any large fish of the open sea may bo selected by shark-suckers. Occasionally one fixes itself to the hull of a vessel. To prove the usefulness of shark-suckers, Dr. C. H. Townsend, director of the New York Aquarium, held a shark-sucker two feet long by its tail while it lifted a pall of water that weighed 211 b. Another held on to a pail of water than weighed 241 b. while the pail and water were raised from the ground. A shark-sucker sixteen inches long was placed in a tank that contained other fishes. It immediately fixed itself to a fairly large groper. Both were brought to the surface by a cord tied to the shark-sucker’s tail. The shark-sucker let go when the groper began to struggle.