One of the best known of all the salt-water fishes is the mackerel. This fish lives in enormous shoals, which are always traveling from place to place, and visit the same parts of our coasts at about the same season in every year. Sometimes they are caught in most extraordinary numbers, so that they can be purchased at very small prices. In some cases, indeed, the catch has been so heavy that it has been found quite impossible to draw in the nets, which had to be allowed to sink to the bottom with the fishes still in them.
These nets are generally made with rather large meshes, not quite wide enough to allow the fishes to swim through. When the mackerel are caught they try to force their way through the meshes, but find that they cannot do so. They then attempt to back out. In doing this, however, the thin twine of which the net is made is almost sure to become entangled with their gill-covers, so that they are held prisoners until the net is lifted from the water.
When fully grown the mackerel is about sixteen inches long, and weighs perhaps two pounds.
Sucking-Fishes
Of the sucking-fishes, or remoras, there are about a dozen different kinds, distinguished by the odd sucker-like disk on the upper part of the head, by means of which they can attach themselves firmly to any object to which they wish to cling. They often fasten themselves in this manner to the hulls of ships, and also to the bodies of sharks and the shells of turtles, and so are carried for long distances without any exertion of their own.
So firmly do these odd little fishes cling, that it is most difficult to remove them without injuring them, and the sharks and turtles have no means of forcing them to loose their hold.
It is a very odd fact that the coloring of the sucking-fishes is just the opposite of that which we find in almost all other fishes. Instead of the upper surface being dark it is light, and instead of the lower surface being light it is dark. But when one of these fishes is clinging to a shark it is the lower surface which is seen, not the upper one; for that is pressed against the body of the shark; and in order to prevent its enemies from seeing and eating it, the lower parts of its body are colored just like the skin of the shark.
Weevers
Strange little fishes are the weevers, two kinds of which are found on the coast of Europe.
Both are highly poisonous, a prick from the spines of the upper fin or the gill-cover being almost as serious as the sting of a scorpion. The poison lies in a deep double groove on each spine, and as the fishes have a habit of burying themselves in the sand at the bottom of shallow water, with only just the sharp spines projecting, they are rather apt to be trodden upon by bathers.