SOLE. Soles are a group of Flat-Fishes (Pleuronectidae), which is represented by numerous species in all suitable localities within the temperate and tropical zones; they become, however, scarce in the southern parts of the southern temperate zone, and are absent altogether in some districts—for instance, on the coasts of southern Australia. Many of the species enter fresh water freely, and some have become thoroughly acclimatized in it. Soles are a highly specialized type of flat-fish; their mouth is very narrow, twisted round to the blind side, and small teeth are developed on that side only. As they always lie or swim on one side, the pectoral fins have ceased to have a function, and consequently these organs are reduced in size, and in many of the species are mere rudiments or are lost entirely. The eyes are small, invariably on the right side of the fish, the upper occupying a position more or less in advance of the lower. Soles are littoral fishes, inhabiting sandy bottoms, shifting with the season from shallow into somewhat deeper water. Like all flat-fishes they are carnivorous, but feed on small animals only; none attain to a large size, scarcely exceeding that of 2 feet. Of the forty species known of the genus Solea, four are found on the British coast; the one most generally known and commercially most important is the Common Sole (Solea solea) ; it seems to occur in greater or less abundance on all flat coasts of Europe, but its numbers have been considerably thinned within the last quarter of a century, at least on the British coasts, doubtless in consequence of the introduction of the trawl. At any rate, that over-fishing is the cause of the decrease of this valuable table fish is amply proved by the fact that simultaneously with the quantity the average ...weight of the fish has been diminished, soles of 12 inches in length and of 8 ounces in weight being now in many localities the largest that can be obtained. At present young specimens form the majority of the soles in the market, and are sold under the names of “slips” or “tongues.” During the breeding-season, which falls in the months from February to April, soles lose much of their flavour. It is a singular fact that male soles seem to be almost unknown, and some ichthyologists account for it by supposing that the males remain much smaller than the females, and are overlooked in consequence. The Lemon Sole (Solea aurantiaca) is much less esteemed than the common sole, and more rarely seen in the market, probably because it is locally distributed in deeper water. It is of a yellow colour, marbled with brown and irregularly spotted with black; the pectoral fin is ornamented with an ovate black spot on its hinder half. Even when this bright coloration has disappeared in the fish after death, it may always be distinguished from the common sole by its large dilated nasal opening on the blind side, which is surrounded by a broad fringe. The Variegated Sole (Solea variegata) is at times taken in considerable numbers on the south coast by means of the trawl, and esteemed as a table fish. It differs from the two preceding species by the rudimentary condition of the pectoral fins, that of the blind side being minute. The colour is brown; darker bands cross the body, and are darkest on the dorsal and anal fins, where they appear as a row of about six large spots. It does not appear to grow to the same size as the common sole. The fourth British species, Solea minuta, is still smaller, not much exceeding 5 inches in length; it is therefore not of commercial importance, although it may be caught at times in the trawl in large numbers. As in the preceding species, the pectoral on the blind side is minute, but that of the right side is large enough to show a distinct black spot. The colour of the body is brownish or greyish, with small black spots, and every sixth or seventh ray of the dorsal and anal fins is black.
Flat-fishes resembling soles abound on the shores of the Indian Ocean beside the true soles, but they have the eyes on the left side of the head and lack pectoral fins altogether. They have been referred, therefore, to distinct genera, such as Plagusia and Cynoglossus.
