Wa. hington, 1908

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FISHES IN THEIR RELATION TO THE
MOSQUITO PROBLEM # * * #

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From BULLETIN OF THE BUREAU OF FISHERIES, Volume XXVIII, 1908

Proceedings of the Fourth International Fishery Congress - = Washington, 1908

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WASHINGTON : : : : : : GOVERNMENT PRINTING OFFICE : 2: 3: 3 3 > 1910

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Issued April, 1910

FISHES IN THEIR RELATION TO THE MOSQUITO PROBLEM
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By William P. Seal

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Paper presented before the Fourth International Fishery Congress
held at Washington, U. S. A., September 22 to 26, 1908

831

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FISHES IN THER. RELATION TO THE MOSQUITO PROBLEM.

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By WILLIAM P. SEAL.

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Some phases of the mosquito problem are extremely simple and easy of
solution, but there are others that have not as yet attracted much attention
and that, in the opinion of the writer, will not be so easily solved. ‘The class
of mosquitoes represented by the rain-barrel wigglers constitutes, with the
salt-marsh species, the most of the mosquitoes, and the most pestiferous of
them as mere annoyances. The problem of dealing with these is one of simple
engineering, filling and draining, with the oil barrel as an auxiliary.

But the Anopheles mosquito is altogether in another class and will require
a very different and more complex sort of treatment. It is, in fact, to a great
extent a separate problem.

Though fewer in numbers than the other mosquitoes, the Anopheles is
more to be dreaded because of its wary and insidious manner of attack and
of its infectious character. It breeds in both quiet and running water, but
always where there is ample protection for its eggs and larve, among and over
masses of aquatic or semiaquatic plants, conferve, duckweed, lily leaves, drift,
floating dead leaves, and débris. And, lying and moving horizontally on the
water, so completely does it assimilate with its surroundings in both color and
shape that it is only discernible to the sharpest vision, generally only by its
movements, which are sidewise or backward on the surface unless seriously
disturbed, when it wriggles down into the water.

After a series of observations and experiments covering several years the
writer is not convinced that Anopheles can be exterminated by any method so far
advanced, or without very great difficulty and the use of every available agency.
The character and magnitude of the problem are not yet understood. Several
years ago, in an examination of Central Park, New York, Anopheles larvae were
found to be abundant, though up to that time the locality was supposed to be
free from them. They were found in unsuspected places, and not where the
other mosquito larvee were found, and they were found abundantly in other
unsuspected places in New York as well. Moreover, although thousands of

833

834 BULLETIN OF THE BUREAU OF FISHERIES.

dollars have since been spent in the attempt to destroy the breeding places,
they are no doubt still occupied, within gunshot of the stately Fifth avenue
homes and nearer to the beautiful playgrounds of the park. The same con-
ditions will be found to prevail in every city.

The most prolific source of Anopheles supply is the ornamental plant pond,
which is becoming one of the most beautiful features of landscape gardening,
public and private. These aquatic gardens provide Anopheles with habitats
closely approximating the conditions it enjoys in nature, with, however, many
protective advantages. Waters of this character can not be treated with oils
or chemicals without destroying their beauty. Thus it becomes a serious
problem how to destroy this pest and yet preserve the beauty of the ornamental
plant pond.

Anopheles, as well as all other mosquitoes, have numerous enemies in
addition to fishes. All the aquatic beetles and their larve (and they are
numerous), the dragon flies and their larve, the boat flies, the crane flies and
their larve (and where these latter are numerous few mosquito larve will be
found), the water skaters, and many others.

The use of fishes for the purpose of destroying mosquito larve is looked
upon generally as an easy solution of the problem, and numbers of species have
been recommended for the purpose, but so far as Anopheles is concerned the
fishes have been generally useless. It is true that by their presence in the more
open spaces they limit the areas in which mosquitoes would otherwise propagate
in great numbers, and no doubt they destroy some Anopheles, as well as some
of all other species of mosquitoes.

All small fishes, whether of the smaller species or the young of the larger
kinds, will be found to eat mosquito larvae with avidity if supplied to them.
This fact alone can not be taken as evidence of usefulness in this respect in a
natural condition. Nevertheless, there is no doubt that the myriads of small
fishes everywhere on the salt marshes and as well in all open waters, salt and
fresh, prevent by their presence such a multiplication of mosquitoes as would
make life unendurable. In this respect even the most insignificant of the fishes
are useful and merit our gratitude.

In considering the usefulness of fishes in this relation the natural habits
and characteristics of a species are the only safe guides. That they will eat
mosquito larve if confined in an aquarium is to be expected. But will they
do so in a natural condition? Will they seek for them as food? Stagnant
water, where there is an abundance of plant life, affords such a great abundance
and variety of larvae and other low forms of animal life that fishes could hardly
be expected to develop epicurean tastes for particular kinds of larve. They
appear rather to gorge themselves with whatever comes in their way. The

FISHES AND THE MOSQUITO PROBLEM. 83

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great need is that there shall be enough mosquito eaters to consume all the
other food that occurs and all the mosquitoes as well. And this means enormous
numbers of fishes. What this involves is yet to be determined. We have no
adequate conception of it.

While, as has been stated, all fishes have some measure of usefulness, if
only in the way of deterrent effect, there are only a few species likely to be found
in waters in which mosquitoes breed, and especially where Anopheles breeds.
The most important of these are: The goldfish, which are introduced; several
species of Fundulus (the killifishes) and allied genera; three or four species of
sunfish; the roach or shiner; and one or two other small species of cyprinoids.
In addition, there are a few sluggish and solitary species like the mud-minnow
(Umbra) and the pirate perch (Aphredoderus), which live among plants. The
sticklebacks have been mentioned in this connection, but the Atlantic coast
species are undoubtedly useless for the purpose, being bottom feeders, living in
the shallow tide pools and gutters, hidden among plants, or under logs and
sticks at the bottom, where they find an abundance of other food.

In the salt marshes there are myriads of killifishes running in and out and
over them with each tide, while countless numbers of other and smaller genera,
such as Cyprinodon and Lucania, remain there at all stages of the tide. So
numerous and active are all these that there is no possibility of the develop-
ment of a mosquito where they have access. Of the killifishes two species,
heteroclitus and diaphanus, ascend to the farthest reaches of tide flow, but it is a
question as to whether they would prove desirable for the purpose of stocking
landlocked waters, since they are much like the English sparrow, aggressive
toward the more peaceable and desirable kinds. Even Cyprinodon, which would
seem to be a valuable small species for the purpose, is viciously aggressive
toward goldfish and no doubt all other cyprinoids. It is characteristic of all
killifishes that they must be kept by themselves in aquaria. They are the
wolves and jackals of the smaller fishes.

As a destroyer of Anopheles the writer has for several years advocated the
use of Gambusia affinis, a small viviparous species of fish to be found on the
south Atlantic coast from Delaware to Florida. A still smaller species of another
genus, Heterandria formosa, ranging from 1'% inch to 7¢ inch in length for
the males to 1 inch or 114 inches in length for the females, is generally to be
found with Gambusia and is of the same general character. Both of these
species are known as top minnows from their habit of being at the surface
and feeding there; the conformation of the mouth, the lower jaw projecting,
is evidence of such feeding habit. Both are to be found in great numbers in
the South in the shallow margins of lakes, ponds, and streams in the tide-water
regions wherever there is marginal grass or aquatic or seniiaquatic vegetation to

836 BULLETIN OF THE BUREAU OF FISHERIES.

afford them shelter from the predaceous fishes. They are also to be found in
shallow ditches and surface drains where the water is not foul, even where it is
but the fraction of an inch deep. In fact, if any fishes will find their way to the
remotest possible breeding places of the mosquito it will be Gambusia and
Heterandria. And they are the only ones, so far as the writer’s observation
goes, that can be considered at all useful as destroyers of Anopheles larve.

To what extent they could be acclimated in northern waters has yet to
be determined. They are to be found in the Ohio Valley as far north as south-
ern Illinois, hundreds of miles above tide water, where the climate must be
quite severe. In 1905, at the earnest request of Prof. John B. Smith, state
entomologist of New Jersey, the writer planted about 10,000 Gambusia and
Heterandria in New Jersey waters. Some 8,000 were planted in one locality
which was thought to afford very favorable conditions. In 1907 Mr. Henry
W. Fowler, ichthyologist of the Academy of Sciences of Philadelphia, and
author of ‘‘ Fishes of New Jersey,’’ found considerable numbers of Gambusia in
the vicinity of Cape May, some 90 miles from where the plant was made. This
opens up a very interesting question. Mr. Fowler contends that Gambusia
should be considered as indigenous to New Jersey. Very strong arguments
to the contrary can be advanced, but the question is not of importance
in connection with this paper, except that it either gives a farther northern
range to the species or that, on the other hand, it shows the possibility of
introducing them.

The writer has come to the conclusion, after many experiments in small
ponds, that a combination of the goldfish, which is ornamental and useful in
the open water, the roach or shiner, which is a very active species, two small
species of sunfish, which live among plants, and the top minnow would probably
prove to be more effective in preventing mosquito breeding than any other
fishes. The goldfish is somewhat lethargic in habit, and is also omnivorous,
but there is no doubt that it will devour any mosquito larve that may come
_ in its way or that may attract its attention. The one great objection is that
it grows too large and that it is cannibalistic, so that when a pond is once stocked
with large goldfish the number of young to survive will be small.

The roach is probably the most widely distributed and abundant of all
the small fishes except the cyprinodonts. It is a very active fish, always ranging
about in search of food.

The two small species of sunfish, of the genus Enneacanthus, are very widely
distributed. They live wholly among plants and feed upon larve of all kinds.

The top minnows are foragers always on the move in the search for food,
skimming over the tops of plants with restless energy.

All of the above-mentioned species are among the most abundant wherever
found. If the range of the top minnows can be extended north it will prove to

FISHES AND THE MOSQUITO PROBLEM. 8

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be a valuable aid. They are quite prolific, throwing off young to the number
of perhaps 10 to 20 at intervals of about a week from April to October. The
young of May will be breeding by July or August the same year, thus giving
a second generation in one summer.

But notwithstanding all that has been said, it is a question in the mind
of the writer whether any combination of fishes will prove effective as against
the Anopheles genus of mosquitoes under present conditions of growing orna-
mental aquatic plants. There must be a change in the construction and
management of the water garden. As these are under the charge of intelligent
men, it is only necessary that the problem should be understood and that
the laws should compel the eradication of Anopheles and provide for an espio-
nage over the places where it breeds. But until some organized branch of
the state governments takes up an investigation of this phase of the problem
in a comprehensive manner nothing will be done. The magnitude of the task
is not yet comprehended. It is quite possible that all of the beautiful masses
of aquatics can be grown on mud alone without destroying their ornamental
character, leaving the large open ones to the water in such a way that the fishes
can do their work easily. In the great wild areas of swamp and stream aloof
from human abodes the problem is more serious and will tax human ingenuity,
but here only the hunter and fisherman are concerned.

At present the attitude of the public mind toward suggested means of
exterminating mosquitoes is good-naturedly tolerant but incredulous. And
while the children are being crammed with Greek, Latin, and geometry they
do not learn how to prevent the breeding of mosquitoes about their own homes
or how properly to screen the houses in which they live. It is a lamentable
fact that even where mosquitoes are most numerous and virulent not one house
in a hundred, it is safe to say, is mosquito-proof. There is an old saying that
“What is everybody’s business is nobody’s business.’’ Practical work to be
effective must be somebody’s particular business. Local boards of any kind
can not easily run counter to individual sentiments and prejudices. It is the
State alone that can overcome local stumbling blocks and inspire respect, and it is
for this reason that attention is called to the seriousness of this problem and
the suggestion offered that it is worthy of the serious consideration of those
whose interest is in the waters where mosquitoes breed and abound—the fish
culturists and fishermen, represented by the fish and game commissions.

In a paper prepared for the meeting of the American Mosquito Extermina-
tion Society in 1905 the writer advanced the opinion that experimentation with
and the supplying of fishes for the purpose of mosquito extermination is at least
as properly the function of fish and game commissions as that of supplying
them in the interests of sport and recreation, which is as much as can justly be
claimed for trout culture. The mosquito problem involves both the comfort

838 BULLETIN. OF THE BUREAU OF FISHERIES.

and health of all classes of citizens. The desirability of the participation of
fish commissions in the work, however, appears to the writer to be a question
that can only be settled by submitting it to those who would be most nearly
concerned with its practical operation, those engaged in fish-cultural work and
who have at their command the necessary equipment and knowledge.

It may be argued that the study of the mosquito problem should devolve
exclusively upon the agricultural departments. In 1900 or 1901 this question
was suggested by the writer, and the Commissioner of Fisheries then decided
that the work properly belonged to the entomological division of the Agricultural
Department. At first thought this seems a logical conclusion; but when we
come to realize fully the magnitude of the task one is compelled to conclude
that its accomplishment will require the combined efforts of all the available
resources of the States and probably of the National Government.

The fish and game commissions have in their service a body of men whose
duties include an espionage of both the land and waters of the States. By
enlarging their powers and authority there is already available a capable organi-
zation which needs only efficient direction and support to accomplish great
practical results in this direction.

There is another side to the question. The fish and game commissions
do not have to the extent that they should the sympathy and support of the
public in general, the prevailing idea being that they represent the interests
of the sportsmen—gunners and anglers. And from this class alone there should
be a vigorous support for such a development, not only because of the promise
of greater comfort in their outings, but also because of the added popularity
it would most surely give to the work of fish and game commissions and to
legislation affecting the waters. If fish culture is to be progressive it must
enlist the sympathy of all classes of citizens. It must justify itself by its use-
fulness. “Those engaged in it and in fish and game protection should welcome
every opportunity to broaden the scope of fish work. There should be a desire
to extend its popularity by enthusiastic support of any line of investigation
or work which will benefit the public at large. There is now a precedent in
the action of the United States Bureau of Fisheries in collecting and sending
fishes to Hawaii for the purpose of mosquito destruction, and there is no reason
why the fish and game commissions with their trained experts should not coop-
erate in absolute harmony with the divisions of entomology, thus avoiding
the creation of dual functions in state work.