Madagascar clearly belongs to this region. Besides some Gobies and Dules, which are not true freshwater fishes, four Chromides are known. To judge from general accounts, its Freshwater fauna is poorer than might be expected; but, singular as it may appear, collectors have hitherto paid but little attention to the Freshwater fishes of this island. The fishes found in the freshwaters of the Seychelles and Mascarenes are brackish-water fishes, such as Fundulus, Haplochilus, Elops, Mugil, etc.
The following is the list of the forms of Freshwater fishes inhabiting this region:—
| Dipnoi [Australia, Neotrop.]— | ||
| Lepidosiren annectens | 1 | species. |
| Polypteridæ | 2 | „ |
| Percina (Cosmopol.)— | ||
| Lates [India, Australia] | 1 | „ |
| Labyrinthici [India] | 5 | „ |
| Ophiocephalidæ [India] | 1 | „ |
| Mastacembelidæ [India] | 3 | „ |
| Chromides [South America]— | ||
| Chromis | 23 | „ |
| Hemichromis | 5 | „ |
| Paretroplus | 1 | „ |
| Siluridæ— | ||
| Clariina [India] | 14 | „ |
| Silurina [India, Palæarct.] | 11 | „ |
| Bagrina [India] | 10 | „ |
| Pimelodina [South America] | 2 | „ |
| Ariina[23] [India, Australia, S. Amer., Patagonia] | 4 | „ |
| Doradina [South America]— | ||
| Synodontis | 15 | „ |
| Rhinoglanina [India] | 2 | „ |
| Malapterurina | 3 | „ |
| Characinidæ [South America]— | ||
| Citharinina | 2 | „ |
| Nannocharacina | 2 | „ |
| Tetragonopterina— | ||
| Alestes | 14 | „ |
| Crenuchina— | ||
| Xenocharax | 1 | „ |
| Hydrocyonina— | ||
| Hydrocyon | 4 | „ |
| Distichodontina | 10 | „ |
| Ichthyborina | 2 | „ |
| Mormyridæ (Gymnarchidæ) | 51 | „ |
| Cyprinodontidæ— | ||
| Carnivoræ [Palæarct., India, S. America— | ||
| Haplochilus [India, South America] | 7 | „ |
| Fundulus [Palæarct., Nearct.] | 1 | „ |
| Cyprinidæ [Palæarct., India, North America]— | ||
| Cyprinina [Palæarct., India, N. America— | ||
| Labeo [India] | 6 | „ |
| Barynotus [India] | 2 | „ |
| Abrostomus | 2 | „ |
| Discognathus lamta[24] [India] | 1 | „ |
| Barbus [Palæarct., India] | 35 | „ |
| Rasborina [India] | 1 | „ |
| Danionina [India]— | ||
| Barilius [India] | 3 | „ |
| Abramidina [Palæarct., India, N. America]— | ||
| Pelotrophus | 2 | „ |
| Kneriidæ | 2 | „ |
| Osteoglossidæ [India, Australia, South America]— | ||
| Heterotis | 1 | „ |
| Pantodontidæ | 1 | „ |
| Notopteridæ [India] | 2 | „ |
| 255 | species. |
Out of the 39 families or groups of freshwater fishes 15 are represented in the African region, or three more than in the Indian region; however of two of them, viz., the Ophiocephalidæ and Mastacembelidæ, a few species only have found their way into Africa. On the other hand, the number of species is much less, viz. 255, which is only two-fifths of that of the known Indian species. The small degree of specialisation and localisation is principally due to the greater uniformity of the physical conditions of this continent, and to the almost perfect continuity of the great river systems, which take their origin from the lakes in its centre. This is best shown by a comparison of the fauna of the Upper Nile with that of the West African rivers. The number of species known from the Upper Nile amounts to 56, and of these not less than 25 are absolutely identical with West African species. There is an uninterrupted continuity of the fish-fauna from west to the north-east, and the species known to be common to both extremities may be reasonably assumed to inhabit also the great reservoirs of water in the centre of the continent. A greater dissimilarity is noticeable between the west and north-east fauna on the one hand, and that of the Zambezi on the other; the affinity between them is merely generic; and all the fishes hitherto collected in Lake Nyassa have proved to be distinct from those of the Nile, and even from those of other parts of the system of the Zambezi.
Africa, unlike India, does not possess either alpine ranges or outlying archipelagoes, the fresh waters of which would swell the number of its indigenous species; but at a future time, when its fauna is better known than at present, it is possible that the great difference in the number of species between this and the Indian regions may be somewhat lessened.
The most numerously-represented families are the Siluroids, with 61 species; the Cyprinoids, with 52; the Mormyridæ, with 51; the Characinidæ, with 35; and the Chromides, with 29. There is not, therefore, that great preponderance of the two first families over the remaining, which we noticed in the Indian region; in Africa there is a comparatively greater variety of distinct Freshwater types, imparting to the study of its fauna an unflagging pleasure such as is scarcely gained by the study of the other region. With the forms peculiar to it there are combined those of India as well as South America.
In Tropical Africa there are still remnants of Ganoids: Protopterus (Lepidosiren) annectens and Polypterus bichir, with the singularly modified Calamoichthys. The two former range from east to west, and are accompanied by an Osteoglossoid (Heterotis) which has hitherto been found in the Nile and on the West Coast only.
Autochthont and limited to this region are the Mormyridæ, Pantodontidæ, and Kneriidæ, a singular type, somewhat akin to the Loaches. Of Siluroid genera the most characteristic are Synodontis, Rhinoglanis, and the electric Malapterurus; of Characinoids, Citharinus, Alestes, Xenocharax, Hydrocyon, Distichodon, Ichthyborus.
The regions with which Africa (like India) has least similarity are, again, the North American and Antarctic. Its affinity with the Europe-Asiatic region consists only in having received, like this latter, a branch of the Cyprinoids, the African Carps and Barbels resembling, on the whole, more Indian than Europo-Asiatic forms. Its similarity to Australia is limited to the two regions possessing Dipnoous and Osteoglossoid types. But its relations to the two other regions of the equatorial zone are near and of great interest.
1. Africa has, in common with India, the Siluroid group of Clariina, the Silurina, and Bagrina; and more especially the small but very natural family of Notopteridæ, represented by three species in India, and by two on the west coast of Africa. It would be hazardous to state at present in which of the two regions these fishes first made their appearance, but the discovery of remains of Notopteridæ and Silurina in tertiary deposits of Sumatra points to the Indian region as their original home. We can have less doubt about the other fishes common to both regions; they are clearly immigrants into Africa from the East, and it is a remarkable fact that these immigrants have penetrated to the most distant limits of Africa in the west as well as in the south,—viz. the Labyrinthici, represented by two genera closely allied to the Indian Anabas; the Ophiocephalidæ and Mastacembelidæ, a few species of which have penetrated to the west coast, singularly enough being absent from the eastern rivers; the Ariina, represented by several species, of which one or two are identical with Indian, having extended their range along the intervening coasts to the east coast of Africa. The Cyprinoids also afford an instance of an Indian species ranging into Africa, viz. Discognathus lamta, which seems to have crossed at the southern extremity of the Red Sea, as it is found in the reservoirs at Aden and the hill-streams of the opposite coast-region of Abyssinia.