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 ‘Teport 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 larvie, pupae, and 
eges 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, larve, and pupa, 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 pre ‘alent 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, t 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 with a variety of small fishes. Reduction of 
the vegetation also diminishes the supply of fish food. 
The common sunfish (Hupomotis gibbosus) is the most useful 
species for ponds and lakes generally. With it may be associated 
the long-eared sunfish (Lepomis auritus), roach (Abramis chrysoleu- 
cus), some of the smaller minnows, black bass, etc. If there is much 
8 Barney, R. L., and Anson, B. J.: Life History and ‘Eeology of the Pigmy Sunfish 
(Elassoma zonatum). Ecology, Vol, I, No. 4, October, 1920, pp. 241-256. 
