NATURALISTIC METHODS OF MALARIA CONTROL 
351 
which many invertebrates and vertebrates 
certainly possess, been intensified into suc¬ 
cessful naturalistic control. 
This subject has been reviewed by Hin- 
man (1934b). As he noted, one should re¬ 
member that a predator that devours large 
numbers of larvae in an aquarium may not 
do so under natural conditions where per¬ 
haps its normal food takes preference. 
However, there have been successes in deal¬ 
ing with certain insect pests of agriculture 
by utilizing predators (Sweetman 1936). 
Fishes that have been most useful in mos¬ 
quito control belong to the order Cyprino- 
dontes, of which the two chief families are 
the oviparous Cyprinodontidae, including 
Panchax, and the viviparous Poeciliidae, 
including Gambusia and Lebistes. The 
males of the Poeciliidae family are differ¬ 
entiated from those of the Cyprinodontidae 
by having an elongate anal fin which is de¬ 
veloped into an organ of copulation. Le- 
bistes reticulatus (“guppies” or “Barba- 
does millions”) is very prolific and has had 
considerable value in the West Indies and 
northern South America, especially in yel¬ 
low fever prophylaxis. But the most im¬ 
portant fish as regards malaria control is 
Gambusia, to some extent G. holbrookii, 
indigenous from Florida to Virginia, but 
chiefly G. affinis Baird and Gerard, of the 
Mississippi Valley, Texas, and North-East¬ 
ern Mexico (Rockefeller Foundation 1924; 
Coveil 1931a). 
This discussion will be limited to Gam¬ 
busia affinis, which Hildebrand (1921) 
has called “by far the most important 
natural enemy of the mosquito known to 
date.” The usefulness of these fishes de¬ 
pends on the following characters which 
they possess: (a) habitat corresponding 
closely with that of larvae; (b) alertness 
and tendency to push into emergent and 
floating vegetation; (c) a high food-prefer¬ 
ence index for larvae in natural surround¬ 
ings; (d) a remarkable fecundity and a 
rapid rate of reproduction in nurseries and 
natural bodies of water; (e) hardiness and 
adaptability to waters deep and shallow, 
open and confined, clean and organically 
polluted, sweet and brackish, in tropical 
and temperate climates; (f) ability to 
withstand handling and transport; (g) 
worthlessness as food for man; (h) infre¬ 
quency with which they have been known 
to be destructive to other fishes. 
In the southern United States Gambusia 
usually can be obtained locally without 
difficulty, but to insure a ready supply it 
is advisable to choose a small shallow pond, 
having an area of 500 to 1000 square yards, 
for breeding of fishes. This stock pond, or 
hatchery, should be cleared of large fishes 
by seining with a fine fish net, or by drain¬ 
ing and cleaning if it can be easily refilled. 
It is also possible to kill all fishes in a pond 
by exploding sticks of dynamite. The 
hatchery can then be stocked with from 100 
to 1000 or more Gambusia. For propo- 
ganda purposes and to safeguard the fishes 
from use as live bait by fishermen, a sign 
post may be erected calling attention to the 
fact that the pond is a Gambusia nursery 
of the Health Department. At suitable 
places in the pond screened shelters of 
3/16 inch wire netting may be built to shel¬ 
ter young Gambusia from cannibalistic 
parents. If the stock pond has an outlet 
this should be screened with 14-16 mesh 
wire to prevent escape of the minnows. 
Inlets should be screened to prevent en¬ 
trance of other fishes. 
Gambusia fishes can be collected by using 
a small net, some three feet deep on a 
12-foot handle or by use of a long bobbinet 
seine. For transportation, ordinary 5 to 
10 gallon milk cans may be used, filling 
with water up to the point where the can 
narrows and using no stopper or else one 
with large perforations. Not more than 30 
to 40 Gambusia should be transported in a 
10-gallon can. 
Gambusia in the latitude of the south¬ 
ern United States will have broods, de¬ 
pending on size of female, of up to 100 or 
more, averaging about 30, every 4 to 6 
weeks from May or June to September or 
October. The fishes arrive at sexual ma¬ 
turity in 4 or 5 months. Gambusia will 
not survive northern winters out-of-doors, 
but if pools and ponds are restocked in the 
