Loach, a soft-rayed cyprinoid fish, of the genus colitis (Linn.). The common loach of Great Britain (C. oarhatula, Linn.) is 3 or 4 in. long, with a small head, elongated body very little narrowed at the tail, and covered with minute and slimy scales; the mouth is small, without teeth, the upper lip having four barbules in front and one at each corner; the ventral fins far back, placed under the single small dorsal; gill openings small, and branchi-ostegous rays three. It is common in shallow clear streams, where it delights to lurk under stones, and is very restless and active when disturbed. Like other species with barbules, it is a ground fish, feeding on worms and aquatic insects; a common name for it is mud creeper; it is very prolific, spawning in March or April, and its flesh is considered a great delicacy. The air bladder is contained in a bony cavity attached to the anterior vertebrae, and is supposed by Weber to be connected with the organ of hearing; there is also said by Yarrell to be a deficiency in the upper wall of the skull between the parietal bones.
The spined loach (0. taenia, Linn.; genus botia, Gray) is rather smaller and more slender, without barbules, but with a forked and movable spine behind each nostril on the suborbital bone; this is a rarer fish in Europe, but several allied species are found in the Ganges. The color in both these species is yellowish white above, clouded and spotted with brown, but unspotted beneath. The lake loach of Europe (C. fossilis, Linn.) is about the same size. All the species of loach are peculiarly restless during stormy weather, especially when accompanied by thunder and considerable electrical changes in the air; they have been regarded as a kind of living barometers, which, from their being ground fish with a low degree of respiration and consequent great muscular irritability, may be explained on philosophical principles; the peculiarity of the air bladder may enable them to perceive thunder either by the sense of hearing or feeling. According to some writers the lake loach, which is very tenacious of life, comes to the surface in order to swallow air, from which it extracts the oxygen, giving out carbonic acid by the vent, performing a kind of supplementary intestinal respiration.
The four-eyed loach or peeper, ranked by Linnaeus in the genus cobitis, but now placed in the genus anableps (Artedi), has been described under the latter title.
Loach (Cobitis barbatula).