FISHERIES 251 



duced to new water which is seldom fished, trout may breed in 

 large numbers, eat up their food supply and so become small and 

 ill-conditioned. Dr. S. F. Bush (1933) of Natal University College 

 has recently started work on this subject in South Africa, where 

 also the Cape piscatorial society has been active in ascertaining the 

 best conditions for sporting fish. Mr. R. E. Dent in Kenya has 

 collected valuable information which is included in a chapter on 

 trout in a book by S. and E. B. Worthington (1933), where other 

 matters relating to East African freshwater fisheries are discussed at 

 some length. Dent's studies are being carried further by Mr. H. 

 Copley, who is devoting attention to the food supply for trout in 

 Kenya streams. 



Since trout need cold water (less than 60° F.) for breeding, they 

 cannot enter into serious competition with the indigenous warm- 

 water fish. The altitude down to which they will thrive varies 

 roughly according to the distance from the equator; in Kenya 

 the lower limit of breeding is about 7,000 feet, in Tanganyika on 

 the Western Usambaras 5,500 feet, and in Nyasaland about 4,500 

 feet. Where fish are required for distribution at lower altitudes, as 

 in Kenya, an indigenous 'carp' ( Tilapia nigra) has been used with re- 

 markably good results . The most interesting experiment was made in 

 Lake Naivasha, where this fish was introduced in 1 925. In the course 

 of three years it had multiplied in such numbers that a predator 

 fish could be introduced to feed on it, and since there is no suitable 

 indigenous fish, the large-mouthed black bass, a native of America 

 which has been naturalized in parts of Europe, was taken to Lake 

 Naivasha. This species has multiplied in its turn so that the lake, 

 which is within easy reach of the settled parts of Kenya, is much 

 frequented for sport, and adjoining land has risen markedly in 

 value. Lake Naivasha lies in an entirely closed drainage system, 

 separated by ranges of mountains from the major rivers of East 

 Africa, so that there is no risk of the black bass escaping to any 

 other water and causing damage to other fish. The introduction 

 of the same fish to open drainage systems in South Africa and 

 Southern Rhodesia, however, is an experiment which appears to be 

 fraught with considerable danger to indigenous species in the 

 rivers concerned. 



Lake Bunyoni in the Kigezi district of Uganda has been the 



