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Mormyr

1911 Encyclopedia Britannica

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The mormyrs (Mormyridae) are one of the most remarkable families of the Malacopterygian fishes, confined to the fresh waters of tropical Africa and the Nile. About loo species, referred to two sub-families and ten genera, are now known, a great number of new forms having recently been discovered in the Congo. They are curious-looking, highly aberrant fishes, very variable in the extent of the vertical fin and in the form of the body, and especially the head, which may be either extremely abbreviated or elongated into a rostrum, with or without a dermal appendage or " feeler." The shape of the head has suggested many of the specific names which have been given to these fish, such as elephas, tapirus, tamandua, caballus, ovis, ibis, numenius, &c. Some forms are eel-shaped. The mormyrs are further remarkable for the enormous development of the brain and for the problematic organ which surmounts it; also as being among the few fishes in which an electric organ has been discovered. This organ, situated on each side of the caudal region, is derived from the muscular system and is of feeble power; it was long considered as " pseudoelectric." Very little is known of the habits of these fishes. Professor G. Fritsch, of Berlin, during his stay in Egypt for the purpose of experimenting on electric fishes, observed that they perish very rapidly when removed from the water, and he had the greatest difficulty in keeping some alive in an aquarium for two or three days. Captain S. Flower has recently been more successful, and the mormyrs have proved a great success in the Gezira aquarium, near Cairo, examples of the species having lived from ten to twenty-six months. The species with comparatively large mouths feed principally on fishes and crustaceans, the others on tiny animals and vegetable and more or less decomposed matter. P. Delhez, on the Congo, found that many are attracted to the borders of the river in the neighbourhood of human dwellings, where they feed on the refuse thrown into the water. It is probable that the species with a rostrum use it to procure small prey hidden between stones or buried in the mud, and that the fleshy mental appendage with which they are provided is a tactile organ compensating the imperfection of the vision in the search for food. Until quite recently absolutely nothing was known of the breeding-habits and development. To the late J. S. Budgett we owe some very interesting observations made in the Gambia on Gymnarchus niloticus, which makes a nest, and the larvae of which are provided with filamentous external gills.

Venerated by the ancient Egyptians, the mormyrs are often represented on hieroglyphics and mural paintings as well as in bronze models. The " Oxyrhynchus," remarkable for its long, curved snout, is the most frequently depicted. A revision of the Mormyridae has been published by G. A. Boulenger in the Proc. Zool. Soc. (1898), with a bibliographical index to the various anatomical and physiological contributions. The skull has been minutely studied by W. G. Ridewood, Journ. Linn. Soc. (Zool. xxix., 1904, p. 188). Figures of the most remarkable forms will be found in Boulenger's Poissons nouveaux du Congo, Ann. Mus. Congo (Zool. i. and ii., 1898-1902), and in his Fishes of the Nile (London, 1907, 4") On the breeding habits of Gymnarchus, cf. J. S.

Budgett, Trans. Zool. Soc. (1901), xvi. 126. (G. A. B.)