"Preferring sandy or muddy shores, the place of the flat-fish is close to the ground; where, hiding their bodies horizontally in the loose soil at the bottom, with the head only slightly elevated, an eye on the under side of the head would be useless; but as both eyes are placed on the upper surface, an extensive range of view is afforded in those various directions in which they may either endeavour to find suitable food or avoid dangerous enemies. Light, one great cause of colour, strikes on the upper surface only; the under surface, like that of most other fishes, remains perfectly colourless. Having little or no means of defence, had their colour been placed only above the lateral line on each side, in whatever position they moved their piebald appearance would have rendered them conspicuous objects to all their enemies. When near the ground, they swim slowly, maintaining their horizontal position; and the smaller pectoral and ventral fins, on the under side, are advantageous where there is so much less room for their action than with the larger fins that are above. When suddenly disturbed, they sometimes make a rapid shoot, changing their position from horizontal to vertical; and, if the observer happens to be opposite the white side, they may be seen to pass with the rapidity and flash of a meteor. Soon, however, they sink down again, resuming their previous motionless horizontal position, and are then distinguished with difficulty, owing to their great similarity in colour to the surface on which they rest."
The number of species of the flat-fishes diminishes as the degrees of northern latitude increase. In this country we have twenty-three species; at the parallel of Jutland there are thirteen; on the coast of Norway they are reduced to ten; in Iceland the number is but five, and in Greenland only three.
Halibut.
Many of them attain a considerable size, particularly the Halibut (Pleuronectes hippoglossus). In April 1828 a specimen seven feet six inches long and three feet six inches broad was taken off the Isle of Man, and sent to Edinburgh market. Olafsen mentions that he saw one which measured five ells; and we are told by the Norwegian fishermen that a single halibut will sometimes cover a whole skiff. Let us, however, remember that these stories proceed from the country where monstrous krakens and sea-snakes are most frequently seen, and where the mists of the north seem to produce strange delusions of vision. At all events, the halibut is better entitled to the name of maximus than its relation the Turbot, to which that epithet has been improperly applied by naturalists. The turbot, equally esteemed by the ancients and the moderns for the delicacy of its flesh, is often confounded in our markets with the halibut, but may be easily recognised by the large unequal and obtuse tubercles on its upper part.
Turbot.
The number of turbot brought to Billingsgate within twelve months, up to a recent period, was 87,958. Though very considerable quantities of this fish are now taken on various parts of our own coasts, from the Orkneys to the Land's End, yet a preference is given to those caught by the Dutch fishermen, who are supposed to draw not less than 80,000l. for the supply of the London market alone. According to Mr. Low, it is rare along our most northern shores, but increases in numbers on proceeding to the south.
Sole.