EIGENMANN— YELLOW FEVER AND FISHES. 205 



General Gorgas was called to Guayaquil and he started a campaign 

 against the mosquitoes. The yellow-fever mosquito is domestic, liv- 

 ing in the huts and houses of men. In many places drinking water 

 is stored in rain barrels. In these the mosquitoes breed. Each fam- 

 ily rears its own fever mosquitoes. It would be easy to keep mos- 

 quitoes from breeding by covering the water with a film of oil. But 

 the native will have none of it. It was found that a fish in each 

 barrel keeps the water free from mosquitoes and thus prevents the 

 spread of yellow fever if a case is accidentally introduced. 



Various fishes were tried at Guayaquil and two were finally se- 

 lected as best. They are the " huaijas " and the " chalacos " of the 

 Guayaquil fishermen. They are abundant and easily obtained in 

 Guayaquil. 



Recently I obtained specimens of both sorts and found that they 

 are old friends, long known to naturalists as Lcbiasina himacidata, 

 and as Dormitafor latifrons. The latter, the " chalacos " of the fisher- 

 men, is a chuckle-headed fish, of the family Gobiidse. It reaches a 

 length of over a foot and lives principally in the mouths of rivers in 

 the area affected by the tide, all the way from Guayaquil to Cali- 

 fornia. It is therefore available to exterminate mosquitoes in barrels 

 all along the fever-infested coast of western tropical America. A 

 close relative, Dormitator maciilatiis, lives in the same sort of places 

 in the West Indies and on the Atlantic side of the tropical mainland. 



The "huaijas" (Lebiasina himacidata) should in time become 

 even a much more valuable fever eradicator, because it is adjusted to 

 live in much higher altitudes than the chalacos. I have caught it all 

 the way from sea level to 7,000 feet elevation. It can, therefore, be 

 used in the entire fever belt, for yellow-fever mosquitoes do not reach 

 as high as 7,000 feet. I have caught it in great numbers in the most 

 unlikely places. At present it is known to inhabit only the rivers 

 from Lima, Peru, to the region of Guayaquil. It should be possible 

 to introduce it in all the tropical parts of America. Related species 

 extend as far north as Panama. 



I became acquainted with it in Lima and later caught it inland 

 from Paita. About Lima it is known as "liza de agua dulce," or 

 sweet-water mullet. It is used as an aquarium fish in Lima and is 



