This species closely resembles a fossil form. It has nothing to do with the True Dories, but is one of the Coral-fishes, and is placed here for the sake of contrast.
We pass now to the Dories, which recall the Sea-bats in the oval and compressed form of the body. The resemblance to sea-bats is, indeed, so close that the latter are frequently described as dories. The mouth of the members of this family is so constructed that, when opened, the upper jaw is thrust forward, and the whole mouth forms a kind of long tube. Dories inhabit the seas of the temperate regions, two species being fairly common in British waters. The best known of these two is perhaps the John Dory, the largest specimens of which attain to a weight of 18 lbs. Mr. Cunningham has described the very peculiar way in which the dory captures its prey. "It does not," he writes, "overtake it by superior speed like the mackerel, or lie in wait for it like the angler, but stalks it and approaches it by stealth. It is able to do this in consequence of the extreme thinness of its body and the peculiar movement of its hinder dorsal and ventral fins. The dory places itself end on towards the fish it desires to devour, and in this position it is evident that it excites no alarm on the part of its prey. The appearance of the dory, seen in this way, is a mere line in the water, to which no particular significance can be attached. I have not particularly noticed the effect of the ribbons of membrane which project from the dorsal fin. But I have observed that the movements of the dory are very gradual, except in turning; it alters the position of its body by a turn of the tail or side-fins, and then swims forward by vibrating the second dorsal and ventral, a movement which causes very slight disturbance of the water. The appearance of the dory in these actions is suggestive of suppressed excitement, his eyes being fixed on his prey. I do not recollect seeing him actually swallow another fish, but have no doubt that he gets near enough to a sprat, for example, without alarming it, to seize it by the sudden elongation of his curious jaws." The way in which these jaws are elongated is admirably shown in the photograph on page [622].
Passing now to the Mackerel Family, we arrive at a group of considerable importance from an economic point of view. Extremely active, migrating, and predaceous, mackerel swim in shoals and seize their prey with great voracity, hunting merely by sight, and snapping at anything moving through the water, especially if it is silvery, like a small surface-fish. The various species differ greatly in size, ranging from the Common Mackerel of about 18 inches long to the giant Tunny weighing nearly half a ton.
Common Mackerel swim in vast shoals, or "schools," as they are called, and one half a mile wide and at least twenty miles long is on record. Mackerel feed on the young of other fish and small fish generally, and, when these are not to be had, on minute crabs and shrimps. They are very prolific, a single mackerel laying from 430,000 to 540,000 eggs.
Photo by Reinhold Thiele & Co.] [Chancery Lane, W.C.
JOHN DORY.
In the centre of each side is a round black spot surrounded by a pale yellow ring.
The Tunnies are amongst the largest of the surface-fishes of the ocean. Abundant in the Mediterranean Sea, they occur occasionally in British waters. For centuries the flesh of the tunny has been held in high regard as food, and it is frequently seen in the Lisbon markets at the present day. The flesh, which is as red as beef, is cut up and sold by weight. The Bonito closely resembles the tunny, but is a much smaller fish, which preys largely upon flying-fishes, which it follows for long distances.
Peculiarly interesting are the Sucking-fishes. The name by which they are commonly known is bestowed on account of the presence of a large oval sucker, placed on the top of the head and extending backwards over the shoulders—an organ formed by modification of the back-fin. By means of this sucking-disk these fishes are enabled to attach themselves to sharks, turtles, ships, or any large object floating in the sea. The hold which they obtain is so strong that it is almost impossible to remove them by force. Being poor swimmers, this method of transportation enables them to pass rapidly to fresh feeding-grounds.