Old World Knifefishes
The Notopteridae are the family most rich in genera and species except for the Mormyridae (Roberts, 1992) They are easily separated from all other species of the whole superorder by their body shape. They have only a very short dorsal fin or even none at all, and a very long anal fin in which the caudal fin has merged; from this the common name »knifefishes« has derived.
(The term Knife fish is also commonly used for the South American electric fishes of the Order Gymnotiformes, similar in body shape but the dorsal and pelvic fins are absent in all species).
There are four genera:
Genus Notopterus
Genus Chitala
Genus Papyrocranus
Genus Xenomystus
Notopterus and Chitala both live in south-east Asia,
Papyrocranus lives in Africa, these three species do have a dorsal fin; the fourth genus, Xenomystus , living in Africa too, lacks it.
Notopterus and Chitala.
Notopterus with the only species N. notopterus (Pallas, 1769) is the smallest species with a maximum length of 60 cm, it differs from Chitala by well developed pelvic fins, which are rudimentary in the other genus and a rather straight to faintly concave forehead whereas in the four species of Chitala it is distinctly concave. The four species C. chitala (Hamilton, 1822), C. blanci (d’Aubenton, 1965), C. lopis (Bleeker, 1845) and C. ornata (Gray, 1831) can only be distinguished on the basis of their coloration which, however, also changes with age and size. Chitala chitala may reach 150 cm, so does C. lopis (and 20 kg in weight), C. blanci growths up to 80 cm, C. ornata to 100 cm.
Papyrocranus.
The two species of Papyrocranus, P. afer (Günther, 1868) and P. congoenis (Nichols and LaMonte, 1932) only differ in the length and width of the head, P. congoensis having the shorter and wider head, it may grow up to 60 cm in against 80 cm in P. afer. Their common characters which separate them from any other notopterid are the absence of pelvic fins and the extension of the swimbladder into the bones of the skull. Papyrocranus afer 2 occurs in West Africa from Gambia to Cameroon with at least four distinct geographical colour varieties, - more or less marbled or spotted pale on dark ground. P. congoensis is restricted to the Congo basin. This genus has only recently been established by Greenwood, 1963 on the base of its peculiar extension of the swimbladder.
Xenomystus.
Xenomystus nigri 2 (Günther, 1868) is the only species of the genus and widely distributed in coastal rivers of Liberia, from Benin to Angola, Upper Nile, Congo and Chad basins. It has pelvic fins but no dorsal and with only about 20 cm it is the smallest of all notopterids.