18 



U. S. BUREAU OF FISHERIES. 



The study of the natural history and ecology of the pigmy sunfish, 

 Elassoma zonatum^ has been concluded and given publication.^ It 

 appears that this fish, under certain conditions, may have some value 

 in eradicating immature mosquitoes. 



MOSQUITO CONTROL IN NORTHERN WATERS. 



-While in northern States mosquitoes have a less acute relation 

 to public health than in regions where malaria is prevalent, they 

 nevertheless constitute there a distinct menace to health and efficiency, 

 besides being effective in causing a material reduction of property 

 values, especially in regions which are normally resorted to for pur- 

 poses of recreation and recuperation of vigor. During the year Prof. 

 J. P. Moore, temporary investigator, has completed a report upon his 

 observations of the use of fish and other aquatic animals for the con- 

 trol of mosquito breeding in northeastern States. His conclusions 

 and suggestions may be summarized. 



Although 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, nevertheless several species of small fishes and the young of 

 some large ones native to these waters eat mosquito larv«, pupae, and 

 eggs more or less habitually. The most important of these mosquito 

 repressors are the common sunfish, the mud minnow, and the common 

 killifish. 



Fishes are found to be far more detrimental to culicine than to 

 anophelene mosquitoes. While in the aggregate they destroy vast 

 numbers of eggs, larvae, and pupae, and (along with other enemies) 

 probably prevent mosquitoes from becoming everywhere an intoler- 

 able nuisance, the destruction is never complete. Some breeding of 

 mosquitoes continues in nearly all bodies of fresh water even when 

 well stocked with mosquito-eating fishes. This imperfect suppression 

 arises through conditions limiting the efficacy of the fishes, most im- 

 portant of which are (1) the barriers that almost all natural bodies 

 of water afford and which prevent the fishes from finding the young 

 mosquitoes, and (2) the abundance of other food for the fishes. Most 

 native mosquito-eating fishes will not thrive in water contaminated 

 by excess of decaying vegetation or otherwise. 



The most prevalent of the barriers is the shallow water and mar- 

 ginal vegetation. In ponds formed by dams provided with head 

 gates a simple, effective, and economical method of controlling and 

 reducing marginal vegetation is by lowering and raising the water 

 level periodically, thus alternately drying and drowning the plants. 

 In ponds and lakes of fixed level mechanical means of clearing the 

 margins must be employed. 



The most practical method of keeping the per capita food supply 

 low is by overstocking v^ith a variety of small fishes. Reduction of 

 the vegetation also diminishes the supply of fish food. 



The common sunfish {Eupomotis gihhosus) is the most useful 

 species for ponds and lakes generally. With it may be associated 

 the long-eared sunfish {Lepomis auritus) ^ roach {Ahramis cJiTysoleu- 

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



8 Barney, R, L., and Anson, B. J.: Life History and Ecology of the Pigmy Sunfish 

 {Elassoma zonatum) . Ecology, Vol. I, No. 4, October, 1920, pp. 241-256. 



