58 U. S. BUREAtr OF FISHERIES. 



taining an efficient and almost self-operatino- natural moscjuito 

 control. 



These studies also illustrate the general attributes that a species 

 of fish should possess in order to be of value in mosquito control. 

 They are: First, that it will eat mosquito eggs, larvae, and pupae, 

 when accessible, at least as readily as other food; second, that it 

 can maintain itself in the habitat and biota to which the mosquito 

 belongs; third, that it can propagate rapidly under the conditions 

 afforded by the bodies of water concerned ; fourth, that it is abundant, 

 widely distributed, and adaptable ; and, fifth, that it is active and of 

 aggressive habit. There are other qualities requisite for particular 

 conditions, but the usefulness of any species is limited by the de- 

 gree to which it departs from the maximum of the five characteristics 

 named. 



SUMMARY. 



1. No fish to which mosquitoes are more than an incidental item of 

 the diet has been found in the fresh waters of the northeastern States. 



2. Several species of small fishes and the young of some larger ones 

 native to these waters eat mosquito larvse, pupae, and eggs more or 

 less habitually. 



3. The most important of these mosquito repressors are the com- 

 mon sunfish, the mud minnow, and the common killifish. 



4. Fishes are far more detrimental to culicine than to anopheline 

 mosquitoes. While in the aggregate fishes destroy vast numbers of 

 eggs, larvae, and pupae and (along with other enemies) probably pre- 

 vent mosquitoes from becoming everywhere an intolerable nuisance, 

 the destruction is never complete. Some breeding of mosquitoes con- 

 tinues in nearly all bodies of fresh water even when well stocked with 

 mosquito-eating fishes. 



5. This imperfect suppression arises through conditions limiting 

 the efficacy of the fishes, most important of which are (a) the barriers 

 that almost all natural bodies of water afford and which prevent the 

 fishes from finding the young mosquitoes, and (h) abundance of 

 other food for the fishes. Water contaminated by an excess of decay- 

 ing vegetation, or otherwise, favors mosquito production, inasmuch 

 as most native mosquito-eating fishes do not thrive in such water. 



6. The most prevalent barriers are the shallow water and marginal 

 vegetation. 



7. In ponds formed by dams provided with head gates a simple, 

 effective, and economical method of controlling and reducing the 

 marginal vegetation is by lowering and raising the water level peri- 

 odically, thus alternately drying and drowning the plants. In ponds 

 and lakes of fixed level mechanical means of clearing the margins 

 must be employed. 



8. The most practical method of keeping the per capita food sup- 

 ply low is by overstocking with a variety of small fishes. Reduction 

 of the vegetation also diminishes the supply of fish food. 



9. Rapid multiplication of small fishes should be encouraged by 

 providing suitable nesting sites and protection for the fry. 



10. The common sunfish is the most useful species for ponds and 

 lakes generally. With it may be associated the long-eared sunfish, 

 roach, some of the smaller minnows, black bass, etc. If there is much 

 aquatic vegetation, the blue-spotted sunfish will prove a valuable 



