176 MOSQUITO ERADICATION 



abdomen, above and in front of the vent. These spots increase 

 in size and, when they join on the ventral surface, the period of 

 parturition is near. 



The young are extruded singly or in twos and threes; the labor 

 may last from an hour to a day. The proportion of males born 

 to females appears to be about 1 to 8 or 9. As many as six broods 

 a year may be born, each brood ranging from 2 or 3 to 50 or 60. 

 A peculiar fact in connection with the fertilization of the eggs is 

 that, apparently, one copulation is sufficient to produce several 

 broods. 



This little fish is one of the hardiest known. It will live 

 equally well in salt, fresh or stagnant water. In foul or stagnant 



Fig. 119. — Gamhusia affinis, male. (After U. S. Bureau of Fisheries.) 



water, it has been observed to stick its mouth above the surface 

 from time to time, making a sucking noise. The object of this 

 action, it is believed, is to get more oxygen. Its habit of swim- 

 ming near the surface is correlated with the fact that it seeks most 

 of its food near the surface. This habit is what gives the fish 

 its value for anti-mosquito work. 



Gamhusia affinis is a very voracious feeder. One medium- 

 sized female has been observed to eat as many as 165 mosquito 

 larvae in a single .day. The young begin feeding a few hours 

 after they are born, and even at this age, the young fish will 

 swallow a larva half as big as itself. 



THE BARRED KILLIFISH (Fundulus heteroclitus) 



The barred killifish, also known as the mud-fish, pike-minnow 

 and salt-water minnow, is probably one of the most effective 



