Major cultivable species for aquaculture

1.3 Major cultivable species for aquaculture: freshwater

Introduction

All kinds of fishes are not cultivable as they have different feeding habits.
Some of the fish feeds on only plant origin food, so they are called
herbivorous while other fish feeds on insects and its larvae are called insectivorous.
Some other fish feed on only fish, they are called carnivorous and while some
other fish feed on any thing available in the pond ecosystem and are called
omnivorous

In culture practice mostly fish of Carp family are cultured as they do not disturb
the others, grow fast and give good production.

Cultivable  Fresh water fishes

Carps form the largest fish family in the world. They have large scales on the body and lack
teeth. Many carps have a pair of barbels (small hair like processes on the jaw
or on the head) while a few have more than two pairs. Several species
of carps are found in the Indian waters. Among
them catla, rohu and rnrigal are the commonly recommended Indian
major carps. Their characteristics and identification marks are briefly described
here.

1. Catla catla

· Catla (Catla catla) is
found naturally in the major rivers of India. It is characterized by
its big head, high back, heavy body, heavy lower jaw and the mouth opening
upward.

· There are no hair like processes on the jaws.

· The back of the fish is gray while
the sides are white in colour.

· But according to the environmental situation
catla may be darkish in colour.

· Catla generally attains maturity during the
second year.



They mostly feed on
the macro fauna

· The mouth being open upwards they collect their food from the upper surface
of the water. Hence it is known as a surface feeding fish.

· If plenty of feed is
available and in less crowded situation catla fish may grow up to five kilogram
per year. They usually attain an average weight ranging between 800 to 1000
grams per year.

2. Rohu

· Rohu (Labeo rohita) is also found commonly in the Indian
rivers.

· The body is long and round; the
head is small and slightly pointed; the back is bent and slopping down
both towards the front and back.

· The upper and lower lips have fold or
frills. On the upper lip there may be two hair like structures.

· In general rohu has slightly
reddish gray scales; however the scales on the back have dark brownish
colour while those on the underneath and lower sides have less white scales.

· One of the easily
identifying marks is that it has reddish fins (wings).

· Rohu mainly gathers its feed from the middle layers of
water column and hence they are known as
middle feeders. This is in confirmation to the direction of the opening of
the mouth which is situated at the mid point opening forward (as opposed to up
ward or downward opening) making it easy for them to gather the feed at
the middle layers of water.

· When they are young they feed on the micro fauna but as
they grow up they start feeding on the micro flora like algae and decayed
organic materials.

· Besides they also feed on
small worms, shell fishes and other lower forms of aquatic life

· Though rohu can grow up to
3.5 kg weight within a year in the commercial composite fish
culture they are found to grow up to only an average weight ranging between 600
to 1090 grams per year.

·  However it is to be mentioned here that among the
recommended carps for commercial growing, rohu is tastier than others. Rohu
matures in the second year of its life.

3. Mrigal

· Mrigal (Cirrhinus mrigala) also like catla and rohu is
commonly found in the  Indian rivers.

· The body of mrigal is longer and less thicker than rohu.

· The head is small and
pointed,,- The mouth opens downwards; the lower lip has no folds or frills
like the rohu. But the upper lip has two hair like structures called barbels.

· In general the scales are yellowish white in colour though
the. scales at the back have a grayish
look.

· Mrigal matures in the second
year of its life.

· Mrigal gather feed mainly
from the bottom layers of the water column.

· When they are young they feed on micro fauna like
crustaceans and rotifers; but as they grow bigger they
feed mostly on the decaying plant materials.

· They also eat on the algae
and other small plants. Like rohu the average live weight gained in one year is
between 600 to 1000 grams though it has the capacity to grow up to 3 to 3.5 kg per
year under sufficient feed availability

Exotic Carps

There are three exotic carps silver carp, grass carp and common carp are
introduced into India and are recommended
for the composite fish culture.

1. Silver carp

· Silver carp (Hypophthalmicthy molitrix) though native of
China was introduced into India from Japan in 1959 and is now a well
established fish among the fish farmers

· It has a flat body, round mouth opening upward, slightly protruding lower
jaws, small eyes.

· The scales are comparatively smaller and white in colour.

· Silver carp gathers feed from the top layers of water
column and hence like the Indian carp catla is a surface feeder.

· When they are young they feed mainly on the micro fauna
but later they mostly feed on the micro and small plants.

· Though they have the
capacity to grow up to 5.5 kg per year under the composite growing conditions
they are found to attain an average weight between 1 to 2.5 kg per year. This
also matures in the second year of its life.

2. Grass carp

· Grass carp (Ctenopharyngodon idella) was originally found
in the big riversof China and Russia.

· But it was brought to India
from Hongkong. It has flat head, short and round face; lower lips are longer
than the upper one; the mouthis round.

· The back is dark gray and
the lower region and abdomen are white.

· They mature by the end of the 2nd year.

Grass carp feeds
mainly on micro fauna till they are about 1.7 to 1.8 cm long.

· Thereafter they feed mostly on all types of aquatic plants.
They are voracious eaters and can consume
grass and other leaves as n1uch as eight times its body

weight per day and
attains weight up to eight kilogram per year.

· This fish can be extensively grown
to control the aquatic weeds in canals, ponds and lakes.

· Besides aquatic plants grass carp also can eat green fodder
grasses. But in the composite fish culture
people do not bother to feed sufficient- ly the grass carp and hence the
weight gain may be less than the optimum.

· It can also grow in slightly saline
alkaline water.

3. Common carp

· Common carp (Cyprinus
carpio) is originally from Russia and China but has been introduced
to India in 1939 through Sri Lanka. There are three types of common carps:

· (a) common carps with small
scales covered allover the body called scale carp,

· (b) those with shining
3;fid big scales covered all over the body called mirror carp and

· (c) Those with only few
scales on the body called leather carp. However the
scale and mirror carps have become popular in India due to its ability
to survive in hot climate.

· The colour varies from gray
to orange. From the physical shape of view two types of common I carps
are noticed one with big stomach and other with long body.

· The body is flat on both sides. The mouth can be
extended forward as it opens up. The lips are thin and smooth.

· There are four barbels (hair like structures) on the upper
lips with one pair slightly bigger than the
other pair.