316
Relative Value of Certain Larvivorous Fishes from the Punjab
2. Fry of larger carp, such as Rohu [Labeo
rohita (Hamilton)], Mirgal [Cirrhina mrigala
(Hamilton)], Theila [Catla catla (Hamilton)], and
others. Utility of fry of large carps of the family
Cyprinidae as larvivores has also been mentioned
by Thomas [1927], Chatterjee [1933, 1934] and
Prashad and Hora [1936]. When introduced into
the tanks at Lyallpur and Chhenawan, the fry of
carp definitely kept down the incidence of
mosquito larvae. The capacity of carp fry to
devour mosquito larvae was further demonstrated
in the laboratory by feeding them on these larvae,
and in the field by study of their stomach con-
tents which, in addition to mosquito larvae, were
found to contain Crustacea as well, thus de-
monstrating the fact that the fry were top
feeders. But the carp in their adult stage attain
a large size, growing to 3 feet or more in length
and become mostly bottom feeders. It is only in
their early stage ranging in size from 2 to
8 inches, that they feed on mosquito larvae;
3. Small carnivorous species such as those be-
longing to the families Anabantidae, Amb-
assidae and Cyprinidae. These small species
feed on mosquito larvae, and are cultivated in
large number at the Departmental Fish Farm at
Chhenawan. The various species, specially
recommended for stocking tanks and ponds as an
anti-malarial measure by the Department are:
Colisa lalia (Hamilton), Colisa fasciata (Bloch
& Schn.)
(Anabantidae), Ambassis baculis
(Hamilton) (Ambassidae), and Barbus (Puntius)
sophore Hamilton (Cyprinidae) 1 . Gold Fish
(Carassius auratus L.), an exotic species, is also
known to destroy mosquito larvae. The fish is
cultivated at Lyallpur and its introduction in
ornamental tanks is strongly recommended.
CAPACITY TO DESTROY MOSQUITO LARVAE
A. In captivity
(i) Feeding capacity 2 . One specimen of each
of the species Colisa lalia and Ambassis baculis
was kept in a bowl, containing 3¼ lb. of water
and fed continuously for 12 days in the month
of May, on known number of mosquito larvae
each day. The larvae left uneaten in the bowls
at the end of 24 hours were counted. Colisa lalia
was found to have devoured 1,778 larvae during
that period, or 148 larvae per day, and Ambassis
baculis had eaten 1,632 larvae, or 136 larvae per
day (Table I) 3 .
Feeding capacity of Barbus (Puntius) sophore
and Carassius auratus was determined by keeping
three specimens of each species in separate bowls
containing 4 lb. of tank water, and feeding them
in April on known number of mosquito larvae
each day. The larvae left uneaten in the bowls
at the end of 24 hours were counted. Three
Barbus (Puntius) sophore consumed in 15 days
4,101 larvae, giving an average of 90 larvae per
fish per day, and three Gold Fish, in 15 days,
consumed 6,238 mosquito larvae on an average
of 138 larvae per fish per day (Table II).
(ii) Feeding on non-living matter.—Colisa lalia
and Ambassis baculis were fed in an aquarium on
minute pieces of charcoal, as big as mosquito
larvae, early in the morning, when they had been
starved for the whole night. The fish were
hungry and snapped at the particles, but rejected
them soon afterwards.
(iii) Rate of digestion of food. (a) Twenty
Colisa lalia were starved for 48 hours and then
supplied with 3,000 mosquito larvae in an
aquarium. Two to four fish were taken out
at regular intervals and were dissected to examine
their gut contents with the following results :—
Time
15 minutes . .
30 minutes . .
45 minutes . .
60 minutes . .
75 minutes . .
90 minutes . .
Total number of mos-
quito larvae in 20
specimens of Colisa
lalia.
Serial
number
of fish
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
Number of mosquito
larvæ
in
stomach
28
31
28
21
29
11
18
30
23
34
29
22
34
18
26
28
26
29
22
29
511
in
intestine
nil
nil
nil
1
5
3
3
2
8
1
nil
4
5
nil
6
nil
6
4
3
2
53
Total
number
of
mosquito
larvae
consumed
28
31
23
22
34
14
21
32
31
35
29
26
39
18
32
28
32
33
25
31
564
1 The author is indebted to R. B. Dr S. L. Hora'
Director of Fisheries, Bengal, Calcutta, for the identifica-
tion of these species. Coloured illustrations of male and
female of Colisa lalia are given by Innes [1935] on
p. 359, and of Colisa fasciata (male) on page 360:
Ambassidae are illustrated on p. 419-20 and the Barbus
on pages 192 to 200. Figure of Barbus, (Puntius)
sophore is given by Hora and Mukerjee [1938] on Plate
VI, fig. 24.
2 These experiments are not conclusive as, firstly, the
number of specimens used is small, and secondly, the
feeding capacity has been determined during one parti-
cular month. It may vary with the season, and it would
be interesting to investigate the comparative capacity
of these fish to destroy mosquito larvae, in captivity,
during various months of the year.
3 The author is grateful to Mr M. Nazir Ahmad for his
assistance in these experiments.