FISH CONTROL 



173 



up into money, even assuming that such a procedure is prac- 

 ticable. Again, in the writer's opinion, there is no other method 

 so effective for controlling breeding in shallow wells, some kinds 

 of cisterns, low culverts that hold water, etc. It is also believed 

 that fish control, either by itself or in conjunction with ditching, 

 is the best and cheapest method of control for flowing streams 

 and ditches, marshes, swamps and many other types of mosquito 

 breeding-place. 



Fish control has its limitations, however. It is not applicable 

 usually to rain-water pools, since they soon dry up and the fish 



(Photo by E. II. Magoon, C. E.) 

 Fig. 116. — The bucket indicates the water's edge. The water area concealed 

 by the vegetation affords an ideal breeding-place, as it is inaccessible to the 

 larva eating fish, which keep the rest of the pond free from larvae. 



would die. Nor, as already intimated, is it feasible to stock a 

 breeding-place with fish and depend upon their unaided efforts to 

 eliminate mosquito breeding. On the contrary, they will have to 

 be helped from time to time. 





HOW FISH DESTROY LARVAE 



Some interesting observations on the manner in which fish 

 detect and destroy mosquito larvae and on the marvelous self- 

 protective instincts manifested by the larvae are recorded by 

 Hildebrand, 1 who says, in speaking of Gambusia affinis: 



"I took several large Anopheles larvae from dense vegetation and 

 placed them in open water among top minnows. With one larva was a 



1 "Fishes in Relation to Mosquito Control in Ponds," U. S. Bureau of 

 Fisheries, 1919 



