PRACTICAL USE OF NATURAL ElsfEMIES OF MOSQUITOES. 71 



living there frequent the shores in shoals and prey upon the various 

 forms of animal life, mosquito larvae included. Many water supplies, 

 however, contain salt and other chemicals, and are polluted from 

 various sources, even from the excrement of game coming to drink; 

 while temporary collections, such as pools, puddles, and irrigation 

 ditches, contain turbulent, muddy water. The level of the water in 

 these different conditions is very variable, and the temperature of 

 the water goes through great variations within a single day, often in 

 midday the heat rising above the limit which most fishes can stand. 

 A fish which would withstand all these conditions would be very 

 exceptional. While we are considering the question of fish intro- 

 duction, the adaptability of the species to acclimatization, its power 

 of enduring long transportation, and its ability to multiply rapidly, 

 even under adverse conditions, are of vital importance to success. 

 In his travels through the land of Oram (Algeria) in 1892, Mr. Vosseler 

 found a widely distributed species occurring in thousands not only in 

 the springs of salt or magnesia water as well as in the irrigation 

 ditches, but also in the highly polluted, badly smelling pools used 

 to water camels, in which 300 to 400 camels often waded in one day. 

 He found the same species afterwards in pure fresh water, in hot 

 springs, and in brackish water. He also found that it inhabits the 

 subterranean waters of the desert and is probably brought up by 

 boring for artesian wells. One of the officers of the garrison situated 

 in the midst of a salt basin without outlet pointed out to Mr. Vosseler 

 that this little fish eats mosquito larvae, which explained the com- 

 parative absence of mosquitoes in that locality. Mr. Vosseler at- 

 tempted the introduction of these fish into Germany and succeeded 

 very well in spite of inadequate preparation. They began to lay 

 eggs within a week of their arrival, and have become accustomed to 

 proper food. They always prefer mosquito larvae and small crusta- 

 ceans. The fish in question is Cyprinodon calaritanus. The female 

 is 8 centimeters and the male 5 centimeters long. The eggs are 

 attached singly to water plants or stones at the rate of one or two a 

 da}^. Mr. Vosseler states that the excellent qualifications of the 

 species are shared by other members of the same family. In German 

 East Africa at least 2 genera and 5 species are known. 



A BRAZILIAN FISH. 



Excellently practical results are reached in Rio de Janeiro by the 

 use of a small fish known as the ''barrigudo" (Girardinus caudima- 

 culatus) which, in the great prophylactic work carried on in that 

 city under the public-health service, is placed in tanks and boxes 

 where it is impossible to use petroleum, and devours the larvae of 

 mosquitoes most voraciously. 



