FISHES IN RELATION TO MOSQUITO CONTROL. 15 
minnows had to be introduced in order to secure mosquito control. 
A similar condition in the presence of sunfishes, the pumpkin seed 
being the most abundant one, was observed by the writer on the 
Potomac River at Bryans Point, Md., in 1912. 
The size and habitat of the pigmy sunfish suggest that it might be 
of value in the control of the mosquito, but the information obtained 
points to the contrary, for Culex larve were plentiful in unprotected 
places in a certain swamp where this fish was quite common. 
The roach minnow, in confinement, at least, appears to destroy 
mosquito larve, as indicated in the following observation. Two 
minnows were left in a “bait well’? when it was abandoned by bait 
collectors. This well was about 10 feet long and 5 feet wide with a 
depth of about 2 feet. The two minnows kept this well wholly free 
of mosquito larvee for several months. Then an oil distributor came 
by, seeing that it was a favorable place for breeding mosquitoes, and 
not knowing of the presence of the fish, sprayed the well with oil. 
The oil killed the roach minnows, and after it evaporated mosquito 
larvee appeared in countless numbers. 
Goldfish, while probably of very little value in large bodies of 
water where other food is obtainable, are useful in confinement. A 
considerable number of fountains stocked with goldfish were exam- 
ined, and if they were properly built so that all parts were accessible to 
fish, and if fairly free of vegetation and débris, no mosquito larvee 
were present. 
CONCLUSIONS. 
1. Gambusia affinis is especially suitable for antimosquito work 
because: (a) It seeks its food at the surface; (b) it is very prolific; (c) 
it gives birth to well-developed young, therefore requiring no special 
environment for depositing and hatching the eggs; (d) it lives and 
thrives under a large variety of conditions and frequents areas espe- 
cially suitable for the support of mosquito larve; (e) it usually lives 
and multiplies in ponds stocked with predacious fishes, providing it 
has very shallow water for refuge. 
2. Plants which have slightly submerged leaves and stems or which 
form floating masses are the chief sources of protection for mosquito 
larve against the top minnow. Such plants should be removed 
from the water or treated in such a way as to make them uninhabit- 
able for the immature mosquito. 
3. Mosquitoes may breed in water so badly polluted that Gambusia 
is almost instantly killed thereby. 
4, Gambusia affinis is of great value in antimosquito work. It 
eliminates the wriggler completely from ponds which are fairly free 
of protective vegetation and débris. If much protection is furnished 
by vegetation and débris, the immature mosquito is not entirel 
eliminated, but the number reaching the adult stage is greatly renee. 
5. The number of top minnows necessary in a body of water in 
order to secure mosquito control depends largely upon the conditions 
which prevail with respect to places of protection, i.e., a much smaller 
number of Gambusia is necessary, if the water is fairly free of hiding 
places for mosquito larvee against fish, than if the reverse is true. 
