250 SCIENCE IN AFRICA 



and northern fish such as herring or cod would stand Uttle chance 

 of survival if loosed in African waters. Many freshwaters, however, 

 are isolated from each other, and since most fish are incapable of 

 being distributed naturally over land, some productive waters have 

 remained practically barren offish life up to the present day. The 

 introduction of suitable fish to these is therefore important in 

 several ways: new food supplies can be made available; since many 

 good waters are within easy reach of towns, recreation can be 

 afforded to Europeans; the popularity of angling as a rival sport 

 to hunting may have a beneficial effect in the difficult work of 

 game conservation; and the sale of fishing licences is a source of 

 revenue. 



In tropical Africa the high mountain streams are almost devoid 

 of fish, and certain lakes and rivers in the lower lying areas are 

 similarly barren. In Kenya, for instance, the indigenous fish, 

 though extremely abundant in the lower reaches of the rivers, are 

 restricted, with very few exceptions, to waters less than 7,000 feet 

 above sea-level. In Lake Naivasha again, at 6,000 feet, there was 

 formerly only a very small fish of no value. The reasons for this 

 peculiar distribution are to be sought in the recent geological 

 history of the continent and in past climatic changes, while ecolo- 

 gical factors such as water temperature and food supply also play 

 their part. 



To the European in Africa, especially in parts of the Union and 

 in the East African highlands, the lack offish in the streams very 

 naturally suggested trout for the purposes of food and sport; so 

 many introductions of brown and rainbow trout have been made 

 since the beginning of the century, with the result that some of the 

 best trout fishing in the world is now to be had in Africa, especially 

 in Kenya and Natal. During the last few years trout have been 

 established in many of the rivers in Tanganyika, at suitable alti- 

 tudes on Mount Ruwenzori in Uganda, in Nyasaland, and else- 

 where. Trout have also proved successful in the Union of South 

 Africa, and in the Cape Province there are well-developed trout 

 hatcheries at Pirie, King William's Town, Stellenbosch, and Jon- 

 kershock. 



The management of trout fisheries in the tropics and South 

 Africa calls for research on a number of problems. When intro- 



