ON THE RELATIVE VALUE OF CERTAIN LARVIVOROUS FISHES FROM
THE PUNJAB, WITH NOTES ON THEIR HABITS AND HABITATS
By HAMID KHAN, M.Sc., LL.B., Ph.D. (Cantab.), F.A.Sc., Game Warden, Punjab
(Received for publication on 16 January 1942)
IT has been well recognized that fish play an
important part in regulating and controlling the
intensity of malarial infection. In India, from
time to time, various zoologists and medical men
have called attention to the fact that there are
several species of fish in this country which feed
on mosquito larvae [Sewell and Chaudhuri, 1912].
Of late years, literature has been slowly gathering
in volume on the proved utility of Indian fish as
mosquito destroyers. Much of this literature
has been reviewed by Prashad and Hora [1936].
Of the later works, mention may be made of
contributions by Sen [1937], Roy [1938], Hora and
Nair [1938], John [1940] and Job [1941, 1, 2 and 3].
The Fisheries Department in the Punjab has
been making free supply of larvivorous fish from
its Fish Farms to various public bodies, Anti-
Malarial Officers, and Public Health Departments
for the last 12 years or so and also been conducting
various experiments on the capacity of indigenous
and exotic larvivorous fish for destroying mosquito
larvae and on their tenacity to live in stagnant
waters. An opportunity is now taken to present
the results of these investigations in this paper.
MATERIAL AND METHODS
The material for study was collected from tanks
situated on the estate of Punjab Agricultural
College, Lyallpur, and lying in the vicinity of the
Fisheries Laboratory where investigations were
carried out. The tanks are brick laid, fed by canal
water and are mainly used for storing water for
cattle. They are all stocked with larvivorous
fish, and it is interesting to note that mosquito
larvae are rarely found in these tanks, though they
may be present in abundance in the pools formed
in the supply channel, which feeds the tanks.
Sometimes when a tank is understocked, the larvae
make their appearance and further introduction of
these fish soon frees it of the mosquito menace.
The tanks are rich in Crustacea, Rotifers, Diatoms
and Euglena Corixa (Rhynchota), larvae of Coleop-
tera, Diptera, Hymenoptera and a few Gastropods.
Of the aquatic weeds, Hydrilla is met in two of
the four tanks, while decayed leaves and algæ
are present in all of them.
The fish caught from the tanks were killed by
pithing their head with a pair of forceps imme-
diately on capture and brought to the laboratory
for systematic examination of their gut contents.
They were dissected on the day of their capture,
the time that elapsed between the capture and
dissection of the fish varied from 15 to 30 minutes.
The fish were cut open ventrally, the gut removed
on a slide and its contents gently squeezed out
from one end and examined under the microscope. 1
The number of mosquito larvae in a tank was
determined by collecting the larvae with a hand
net, each along four square feet surface area of the
tank 2 . A small conical linen net, 12 inches wide
at the mouth and 24 inches deep, with a bamboo
handle was used. Counting of mosquito larvae
was done by suction with a filter pump, which
was attached to a tap and water allowed to run.
At the suction end of the filter pump a bottle,
fitted with a rubber cork with two glass tubes,
was inserted. One glass tube was connected with
the suction end of the filter pump and the other
tube was used for collecting the larvae which were
placed in a dissecting dish. The larvae as they
were sucked into the glass bottle could easily be
counted in a very short time.
Gaseous analysis of water for determination
of dissolved oxygen was done by modified
Winkler's method as recommended by American
Public Health Association [1936], and of absorbed
oxygen by Forchammers' method [Stocks, 1932].
The amount of carbon dioxide was determined
by Seylers' method as described by Kemmerer,
Bovard and Boorman [1923-24] and pH values
were found by Hellige Comparator.
LARVIVOROUS SPECIES OF FISH IN THE PUNJAB
The larvivorous fishes of the Punjab, according
to the system followed by Prashad and Hora
[1936], may be grouped into three main divisions :
1. Predaceous species, such as Cat-Fishes (Silu-
roidea), and Murrel (Ophiocephalidae). Their
utility as larvivores is marred by their predaceous
habits, as in their adult stage they feed on smaller
species of fish. Introduction of such fish in tanks
where smaller species have been stocked is, there-
fore, not recommended;
1 . The stomachs of Colisa and Ambassis were cut open
and their contents removed. The contents of intestine,
however, were gently squeezed out for qualitative study
of food. Job [1941, 2], recommends slitting open the gut
for allowing the preservative to act on the gut contents.
For qualitative and quantitative study it is desirable to
cut open the gut, wash and remove the contents with
a brush. As the present study was made on freshly
killed fish, it was not considered necessary to cut open
the gut for the action of the preservative.
2 . An approximate estimate of the number of mosquito
larvae and Crustacea present in the tanks was made by
use of hand net. For determination of mosquito-larvae
density, methods described by Christophers, Sinton and
Covell [1936], and Job [1941, 1] are recommended.
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