The Sea Shore

by William S. Furneaux

Most fishes possess a membranous bag containing air, situated just below the backbone, and known as the air-bladder; but this organ does not exist in sharks and rays and in some of the heavier bony fishes that live on the bottom. The air-bladder is capable of being compressed by the action of certain muscles, and its principal use seems to be the adjustment of the specific gravity of the fish to that of the surrounding water; but it is interesting to note that the development of this air-bladder is precisely the same as that of the lungs of air-breathing animals, and that in some fishes which live in foul muddy waters it is really a functional lung by means of which the fishes can breathe direct from the atmosphere.

We can find space to refer only to one other internal structure of the fish, namely, the roe of the female. This usually consists of a very large number of eggs of small size, sometimes numbering many thousands, and even millions, in a single individual. So numerous, indeed, are the eggs, that were it not for the multitudes of carnivorous animals that devour both eggs and fry, the sea and fresh-water lakes and rivers would soon become so thickly populated that the fish would die in millions for lack of food and air.

In some cases, however, the eggs are much larger and fewer in number, but these are generally protected from the ravages of predaceous species by a hard covering, as we shall observe in the sharks and rays.

Finally, a word or two must be said about the distribution of fishes. We have already referred briefly to species that live principally at the surface, and others that make the bottom their home: but some of the former go to the bottom for food or to deposit their spawn, while some of the latter occasionally rise to the surface and swim in shoals. We have noticed, too, that the paired fins of bottom fishes are sometimes modified into feelers, or into fingerlike processes adapted for creeping. Similar organs, employed undoubtedly as organs of touch, and called barbels or barbules, are often developed on the chins or jaws of these fishes.

Although we have to deal principally with the species that belong more or less to the shore—the littoral fishes—we should like to refer briefly to one or two interesting features of those that live at great depths. It will be readily understood that much light is lost as the rays penetrate into deep water, so that the bottoms of deep seas must be more or less darkened. To allow for this loss, we find that the species living at moderate depths are provided with larger eyes to enable them to see their prey and their mates; but at still greater depths, where the sun’s light cannot penetrate, the fishes are either blind, or are possessed of luminous organs which enable them to see their way. Again, as the sea is so thinly populated at such great depths, the carnivorous species do not find abundant food always at hand, hence they are often provided with such mouths and stomachs as will allow them to make the best of favourable opportunities, some being capable of swallowing a fish quite as large as themselves.

We often find fishes roughly classified into fresh-water and salt-water species, and although such a division is at times convenient, it must be remembered that some of the former migrate into brackish and even into salt water, while some of the latter ascend estuaries and rivers either for the purpose of obtaining suitable food, or for the deposition of their eggs.

The fishes that frequent our coasts may be classified into two main groups, those with cartilaginous skeletons (Elasmobranchii), and the bony fishes (Teleostomi). Both these are divided into family groups, and we shall deal more or less briefly with all the important families that include common British marine fishes, but giving more attention to those species that are truly littoral in habit—species that may be found in the rock pools or under stones at low tide, and which may be obtained by the amateur angler working from rocks, piers, &c.

The cartilaginous fishes include the Sharks, Dogfishes, and Rays. They have pouchlike gills, five or more on each side, each one opening to the exterior by a separate slit. The skin generally contains bony elements that are toothlike in structure and often in form; the mouth is usually on the under side of the head, and the tail is nearly always of the heterocercal kind. They are all carnivorous creatures, and often exceedingly voracious; and are represented in our seas by the Rays and Dogfishes.

Rays or Skates (family Raiidæ), of which there are six or seven British species, are readily known by their broad flattened rhomboidal bodies, with the mouth on the under side of the head, a longitudinal fold on each side of the tail, and pectoral fins extending quite or nearly to the front point of the head.

Two of these fishes are very common in our markets, one being the Thornback Skate (Raia clavata), distinguished by the clawlike spines down the middle of the back as well as on other parts of the body; and the Common Skate (R. vulgaris), a very voracious species, from two to four feet long, with a very sharp muzzle.