How to determine a sexully matured fish for breeding

.3.2 Brood fish Sexually ripe and healthy fish are
the prerequisite for any kind of
artificial or semi-artificial
propagation. They can be obtained
from natural waters just prior to
the spawning season, from the spawning ground. wild fish while spawning. Fish gathering in easily detectable shallow spawning
grounds, or migrating in masses toward such places are vulnerable
to easy capture. They can also be
easily captured while actually in
the act of spawning in groups or in
shallow water. The object of such
capture is to procure ripe sexual products for incubation and
rearing under controlled
conditions. Special hatcheries are
generally constructed for this
purpose (for coregonids, common
carp, pike, etc.). This is an old technique, practised mainly in
Europe, for obtaining young fish
for stocking. The coregonids, pike,
common carp, and bream are
propagated by this method. The gear used for such capture are
traps and fyke net for pike, gillnet
for coregonids, simple seine nets
for common carp and bream, and
castnets and covering nets for
common carp and pike. Fish caught this way can be
st ripped easily, since they are
already ripe and in an oozing
condition. Some of them may not
be fully ripe, in which case they
must be held in captivity for a couple of hours before they can
ovulate. The spawners must be
handled with care during the
breeding process. This method
obviates the necessity for building
up and maintaining a brood stock in ponds. 4.3.2.2 Capturing brood fish in their natural habitat. Another alternative to the capturing of
spawning fish from spawning
grounds in the wild, is the capture
of adult wild fish during their
natural breeding time or when
they are migrating to their spawning grounds. This is likely to
yield a good number of ripe
breeders, but these gravid fish are
prone to easy injury during netting
and transport. Moreover, wild
breeders do not easily adjust to life in captivity. They become nervous,
jump about wildly, and may not
feed. In general, their handling is
much more difficult than that of
tamed stock. It is also difficult to
secure adequate numbers of breeders of the required size and
age. It is necessary to use tranquillizers
in the handling and transportation
of such wild fish, particularly if
they are large, as any injuries they
sustain may endanger the success
of the entire breeding operation. A further disadvantage is the high
probability of introducing parasites
into the hatchery. However, this
method also has a definite
advantage in that the farmer does
not have to painstakingly build up and maintain a brood stock in his
farm. Nevertheless, most
commercial hatcheries generally
maintain their own brood stock. 4.3.2.3 Farm rearing of brood stock. In spite of the numerous inherent difficulties, this method is
widely practised all over the world,
since it enables the building-up and
selection of healthy breeders for
eventual stock improvement.
However, proper maintenance of suitable environmental conditions
and adequate food supply is
mandatory. Fortunately, almost all cultivable
fish either attain full sexual
maturity or at least gonadal
maturation up to the “resting
phase” in confined waters. The
river spawners and those that spawn in inundated areas are
difficult cases in this regard, but it
has been possible to breed most of
them through artificial
propagation techniques (e.g.,
Chinese major carps, Indian major carps, and river spawners of the
Orinoco and Amazon basins). In the brood fish ponds, various
factors such as temperature, light,
oxygen content, stocking density,
tranquillity, size, and depth of the
pond and food should generally
approximate the natural requirements of the species
concerned. Therefore, a through
knowledge of these factors is a
prerequisite for the successful
rearing of breeders. Temperature. Even though many fishes can withstand temperature
extremes, it is advisable to rear the
brood stock in a pond where
extreme fluctuations of
temperature do not occur. As
investigations have shown, the normal gonadal development
requires a sum of temperature. The
sum of temperature is expressed in
day-grade. In the temperate be lt of
the world, the gonadal
development of fishes, such as common carp, Chinese carps,
catfish, tench, etc. can be
accelerated by warming up the
environment of the brood fish. The
spawning time can be advanced by
a month by this treatment. During March when the atmospheric
temperature is only 4°–8°C, the
common carp can be made to
ovulate through hypophysation
after warming up its environment
for two weeks. By keeping the common carp brood fish in an
environment of 25°C, it can be
made to breed thrice a year. On
the other hand, its gonadal
maturation can be significantly
retarded by subjecting it to lower temperatures. In temperature,
therefore, the fish culturist has a
handy tool to either advance or
postpone the breeding of a fish. The requirement for illumination varies with different
species. The gonadal development
in salmonids is related to
photoperiods, while in warm water
fishes gonadal development is
adversely affected if the light conditions deviate from the
normal. Many fishes, particularly
catfish, are irritated in illuminated
environments. Turbid waters are
preferred by several species of
fishes, especially river spawners. They become agitated in an
illuminated, transparent
environment, which exercises a
negative effect on their gonadal
development. Even hormone-administered breeders avoid bright light and look for hiding
places. Oxygen. Frequent fluctuations and low levels of oxygen content in
pond water tend to inhibit gonadal
development. To ensure healthy
gonadal development, brood fish
pond water should have an
optimum oxygen level throughout the rearing period. Supplying
fresh, oxygen-rich water,
therefore, is an important
requirement. Stocking density. Although most cultivated fishes are able to
tolerate crowded pond conditions,
the effects of crowded conditions
on gonadal development is often
deleterious. Experience has shown
that 20–50 ripe breeders (weighing 150–250 kg) can be reared in 0.1 ha (1 000 m2) pond area. The number of breeders can further be raised
by stocking fish species of different
feeding habits, as is practised in
polyculture work in India and
China. Combinations in Multi-Species Brood Stock Rearing of Chinese Carp Species No. of fish per ha Average weight of each fish, kg 1. Grass carp as major species: Grass carp 150–200 8–12 Silver carp 60–90 2 Mud carp 600–1 000 0.02–0.05 2. Bighead as major species: Bighead 80–100 7–12 Grass carp 100–120 5 Silver carp 30–50 2 Common
carp 300–500 0.25 3. Silver carp as major species: Silver carp 150–250 3–6 Grass carp 100–130 2 Mud carp 500–600 0.02–0.05 4. Mud carp as major species: Mud carp 1 600–2 300 0.8–1.5 Bighead carp 30–50 5–6 Silver carp 60–100 2–3 In general it is not advisable to
stock would-be breeders along
with market-destined fish,
especially if the latter are fed an
unbalanced diet. However, young
prospective breeders can be reared in restricted numbers along with
ripe breeders. Tranquillity. It is believed that frequent disturbances interfere
with normal gonadal development.
However, the Chinese practice of
netting brood fish once or twice
before hormone administration
and keeping them in crowded conditions (either blocked off by
nets in one corner of the pond, or
suspended in seine nets) serves to
acclimatize the brood fish to
handling and transportation,
reduces post-spawning mortality, and increases the rate of ovulation. Size and depth of pond. The rearing pond for larger brood fish
(2–10 kg or above) should be about 2000–4 000 m2. Smaller brood fish can be raised in smaller
ponds. The depth of brood fish
ponds generally varies from 1 to 2
m. Food. A suitable and adequate food supply is of foremost importance
to brood fish. If the fish are left
hungry or starving, the
vitellogenesis phase of egg
development is affected. If the food
is deficient in essential nutrients, particularly the amino-acids,
vitamins, and minerals, the egg
development is adversely affected,
ultimately leading to the failure in
ovulation. Therefore, breeders
reared on ample natural food or on a protein-rich artificial diet yield
satisfactory results. It is better to
breed a smaller number of brood
fish on qualitatively and
quantitatively satisfactory diet (or
natural food) than to keep a huge stock under half-starved
conditions. The natural diet of
fishes differs from species to
species. It is, therefore, important
to know the food and feeding
habits of the cultivated fish. 4.3.2.4 Age and weight of the breeders. The“first spawners” or “virgins” are usually used for
artificial propagation. Larger fish
produce more eggs, but the
handling of “giants” weighting
over 10–15 kg is rather difficult
and tiresome. The most suitable size of spawners in the case of
common carp, Indian carps, and
Chinese carps is 3–5 kg. Larger
specimens are convenient if
breeders spawn spontaneously
without having to be stripped. Very large fishes are less suitable
for hormone treatment, because of
the requirement of large doses of
hormone and the difficulties in
handling them. The fecundity of medium size fish
(2–6 kg) is generally higher than
that of giant fish. Spawners of 0.5–
2 kg weight are very easy to
handle and strip. Before releasing the breeders in
special spawning ponds for
spontaneous spawning, or before
they are prepared for induced
spawning, the fish culturist should
make sure that they are in a “ready-for spawning condition. Unless their gonads have
developed up to the resting or
dormant stage, they will not
respond to any propagation
technique. Therefore, sorting out of the right breeders is very
important for successful artificial
propagation. 4.3.2.5 Selection of breeders for ready spawning or for hormone treatment. The symptoms indicative of the ready-to-spawn
condition are somewhat similar
among various fishes.How to determine
Females fish for breeding.
1. Well-rounded and soft abdomen,
the fullness of which extends
posteriorly past the pelvis to the
genital opening.
2. The genital opening is swollen,
protruding, and reddish or rose in
colour; its edge is uneven or
fringed.
3. The anus (vent) may also be
swollen and reddish.
4. In some column-living fishes of the
Orinoco river, the abdomen
becomes red coloured. 5. Some fishes develop a nuptial
colour before ovulation.
How to choose male fish for breeding.
1. The male releases a few drops of
thick milt when its abdomen is
pressed slightly.
2. In some male fishes (Chinese carps
and Indian major carps) the dorsal
surface of the pectoral fin becomes
rough.
3. Some male fishes of the Orinoco
and Amazon basins produce a
sound when taken out of the water
(coporo, curimata, curbinata). Many fishes, such as the tench,
exhibit distinctive sexual
dimorphism. It is necessary to
examine the females of some fishes
(grass carp, channel catfish, etc.)
before they are fed, to ensure that the abdominal fullness reflects the
size of the gonads and not gorged
food. Some of the above-mentioned
symptoms may be absent in some
fishes, while there may be
additional symptoms in others. In
the case of cachama (Colossome oculus), the belly of the female becomes soft and rounded only a
little before the actual spawning.
This hard-bellied condition is a sort
of adaptation for the co-existence
of this fish with the aggressive
piranha (caribe). If both sexes are together in the
same pond or cistern, as soon as
the males indicate their readiness
for spawning, the females also
achieve the same condition. Since
the river spawners do not breed in confined waters, there is no need
to segregate their sexes. On the
other hand, the segregation of
sexes is mostly necessary in the
case of pond spawners, since
otherwise it may lead to uncontrolled spawning in the
storing pond (e.g., common carp)
or unnecessary fighting among
males (e.g., catfishes). It is important that the culturist s
carefully observe the brood fish
with respect to their anatomical
and behavioural changes during
their readiness for spawning to
ensure the success of subsequent operations.

Share this: