Photo by A. S. Rudland & Sons.
BICHIR.
A second representative of the Enamel-scaled group.
From the roe of these fishes caviare is made, and isinglass from the inner lining of the air-bladder. But the best-flavoured flesh and the finest caviare are obtained from a comparatively small form, the Sterlet, a species which does not exceed a yard in length. It is common in the Black and Caspian Seas, the Siberian rivers, and the Danube as far as Vienna.
Photo by Scholastic Photo. Co.] [Parson's Green.
BICHIR.
Note the remarkable finlets on the back and the peculiar structure of the breast-fins.
With the Sturgeons we come to the end of the Fan-finned Fishes. The Fringe-finned group are represented to-day only by the Bichir and the Reed-fish. These are extremely interesting forms, if only because they are the sole survivors of a once numerous tribe, the remains of which occur as fossils in some of the oldest geological formations. They are known as Fringe-finned on account of the fact that the rays which support the fin-membrane in the paired fins are ranged round a lobe-shaped base, instead of running directly backwards to the body. As in the bony pike, the body is clothed externally by large quadrangular bony plates of considerable thickness, and coated with a layer of enamel.
The Bichir, which is found in the Nile and other tropical rivers of Africa, is easily recognised by the peculiar structure of the back-fin, which takes the form of a series of detached finlets, varying in number from eight to eighteen. The length attained by the bichir is about 4 feet. Gill-breathing is supplemented by the air-bladder, which is used as a respiratory organ, the expired air escaping by a slit, known as the "spiracle." The young bichir breathes, like a tadpole, by means of large external gills, projecting backwards on each side of the head; later these are replaced by the more efficiently protected internal gills.