fauna op the african lakes. 523 



Pisces. 



The fish of Tanganyika constitute no inconsiderable proportion 

 of the animal forms which are known from the lake, since there 

 are now recorded from its waters no less than 146 species. This 

 result is mainly due to the activities of the three British ex- 

 peditions and more recently the Belgian expedition under the 

 late Louis Stappers, though a number of smaller collections have 

 added considerably to our knowledge. 



There was a period during which the fish fauna of Tanganyika 

 had probably been more carefully investigated than those of the 

 other big lakes, but at the present time this is no longer the case. 

 So far as Victoria JSTyanza is concerned, this is due particularly 

 to the researches of the late "W, G. Doggett, M. Alluaucl. 

 E. Degen, and E. Bayon, while in Lake Nyasa the recent 

 collectors have been F. Fiilleborn and E. L. Rhoades. It is 

 nevertheless very doubtful whether all the fish forms which in- 

 habit these vast inland seas have as yet been even approximately 

 discovered, for each extensive collection still adds new species, 

 often of very striking appearance. At the same time it will be 

 agreed that the investigations of many explorers, spread over 

 a fairly considerable period of years, must have furnished data on 

 which it is possible to rely, even though further knowledge may 

 occasion some revision in points of detail. 



The fishes are better rejoresented in the lakes than an 3^ other 

 group. Nyasa appears to form an exception, as in that case 

 the number of Rotifera even exceeds tha,t of the fishes. This 

 is due to the inclusion of a large number of extra-lacustrine 

 records. 



In the list which follows, 308 species of fish are enumerated, 

 and it is a point of considerable interest that only three of these 

 are recorded from outside the continent. They are Clarices 

 lazera, Tilapia nilotica, and Haplocliroinis desfontainesii, all known 

 fiom Syi'ia, with which, through the valleys of the Jordan and 

 Nile, there is believed to have been communication in former 

 geological times. 



The outstanding features in the case of Tanga,nyika will be 

 seen to be firstly the large number of different forms found 

 M'ithin the limits of a single lake, and secondly the remarkably 

 lai'ge percentage of those forms which are not known to occur 

 elsewhere. 



35* 



