520 On a new Fish from British East Africa. 



white; fins greyish, soft dorsal, anal, and caudal with nume- 

 rous small darker spots which may form vertical bars on the 

 caudal ; ,the latter with the posterior edge of a faint pink. 



Total length GO mm. 



Lake Magadi, a hot soda lake in bottom of Rift Valley, 

 British East Africa, at an elevation of 1980 feet above sea- 

 level. The lake is perfectly isolated, the nearest water being 

 the Southern Euaso Nyiro, a river rising in the Mau plateau 

 and flowing into a natron lake on the boundary of Britisli, 

 German, and East Africa. The fish were caught by Mr. J. 

 W. Graham in warm water (up to 120° Fahr.), and several 

 specimens have been presented by him to the British 

 Museum. 



Special interest attaches to this new Tilapia, one of the 

 smallest of the genus, from the conditions under which it 

 lives. I am indebted to Mr. Graham for the following notes 

 concerning the habits : — 



" The fish were discovered in various isolated springs of 

 soda liquor on the eastern shore of Lake Magadi, a natural 

 soda deposit at the bottom of the 'Great Rift Valley,' in 

 latitude 2° south and at an elevation of 1980' above sea- 

 lavel. In some cases the thermal springs in which the fish 

 are found run out in the form of a very shallow stream (1" to 

 6" deep) over the soda-mud flats ; in others the springs are 

 quite isolated, forming pools, and can have no connection 

 with adjacent springs except during very exceptional rains, 

 and then for but a short time. The temperature of the 

 various springs varies, but the fish have been found in all 

 temperatures from 80° F. to 120° F. Apart from the occa- 

 sional intercommunication between the springs mentioned 

 above, there is no connection at any time with other possible 

 breeding-grounds, fresh water or otherwise. In other words, 

 there are no streams entering the lake nor are there any 

 running out of it. The springs are completely landlocked. 

 The fish are very active in their movements and show great 

 alarm on the approach of human beings. They probably 

 mistake them for birds of prey, although at no time during 

 the two years the fish have been under my observation have 

 any birdt, been noticed to be feeding on them. The principal 

 food of the fish appear to be the green- and pink-coloured 

 algte surrounding the sources of the various springs, and the 

 fish will climb up a trickle of water to the height of a foot or 

 more above the normal soda-liquor level in order to reach 

 this food. The algre are so plentiful as to look like slimy 

 moss around the springs. The fish were breeding in December 

 last, the male making a nest in the sand and females 



