Breeding in catfishes

4.3.3 Induced ovulation and or spawning In its natural breeding ground, a
ripe ready-to-spawn brood fish can
produce ripe sexual products
within a short time when suitable
environmental conditions occur.
Elsewhere, breeding has to be induced. Basically, there are two ways to
induce ovulation (the final ripening
of the eggs) and spawning (the
release of eggs in the presence of
the male) under artificial
conditions.
1. Simulation of suitable
environmental factors, which
would trigger the fish's own
hormones to govern and direct the
final ripening process of the
gonads.
2. Administration of gonadotropic
hormones, which may cause the
final ripening of the gonads. A combination of these two
methods is sometimes adopted, as
in the case of the Chinese technique
of propagation. 4.3.3.1 Inducing spawning without hormone treatment. Some pond spawners can be stimulated to
spawn by providing: a. nests, b. artificial spawning surface
(Kakabans), c. spawning receptacle, or d. conditions simulating the decisive
natural environmental conditions. Some of these methods can also be
combined to obtain even better
results. Induction of spawning by providing nests. This method is commonly practised for the
propagation of nest spawners, such
as pike-perch, European catfish,
etc. The nest used for pike-perch
consists of flat bundles of dry,
bushy roots of willow tree, grasses,
etc. or the same materials fixed on
frames. Today, an old synthetic net
spread between two sticks, and “artificial grass” fixed on a
frame are also used as nests. These
nests are placed on the natural
spawning ground shortly before
the spawning season and are
c hecked for signs of spawning every 2–3 days. The nests with
eggs are collected and transferred
to the hatchery. In the farm, the framed nests (50
cm × 50 cm) are placed on a hard
bottomed storing pond (500–2 000 m2 surface area), at the rate of one nest for every 8–10 m2. Depending on the number of nests, the
re quired number of male and
female pike-perch brood fish are
stocked when the water
temperature is about 10°C. The
nests are checked every 2 or 3 days and those with clumps of eggs are
removed for controlled incubation.
These double-shelled eggs can be
easily transported in boxes or
baskets, taking care to keep them
moist throughout. In the case of European catfish,
tent-like nests are made of dry
bushy roots of willow tree, or
branches of thuja or pine tree.
Then, 3 or 4 of these nests are placed in a pond (1 000–2 000 m2 surface area) and adequate
number of brood fish pair are
released in it. The spawning can be
easily detected because of the
vigorous movements of the
spawners. The nests with eggs are removed for controlled incubation. In the case of some gouramis (e.g.,
the giant gourami), the mere
providing of nest materials can
stimulate nest building and
subsequent spawning. Induction of spawning by providing artificial spawning surface of Kakabans. The Kakabans are mat-like structures measuring a few m2 in area. They are made of dry grass, pine tree branches, or
similar material fixed on a frame.
The Kakabans are either fixed to
the pond bottom with sticks, or are
held about 20–30 cm below the
water surface (Figure 16). The common carp of tropical and
subtropical are as willingly spawn
on Kakabans, scattering their sticky
eggs on this artificial surface. They
do not spawn in muddy bottomed
ponds unless Kakabans are provided. After spawning has
taken place, the Kakabans covered
with eggs are removed from the
pond and transferred to nursery
ponds, where they hatch out and
grow without the danger of becoming infected by parasites
from their parents. This spawning technique can be
easily applied even under primitive
conditions. The Kakabans with eggs
can also be conveniently
transported by covering the eggs
with moist cloth or grass. This technique can also be adopted for
other fish with spawning habits
similar to that of the common carp. Induction of spawning by providing receptacles. Some fish, such as the channel catfish, require
some hiding place while spawning.
They also guard and aerate their
eggs. Usually 45 l milk cans or oil
barrels are used as spawning
receptacles in ponds or closed-off part of ponds. Soon after they are
placed in the ponds, the ripe brood
fish spawn in these receptacles,
from which the eggs are removed
and incubated under controlled
conditions. Other pond-spawning catfish can also be stimulated to
spawn by providing spawning
receptacles (Figure 17). Clay, plastic, or cement-concrete
pipes of larger diameter (20–25
cm) can be used to stimulate
spawning in other fishes, such as
Plecostomus plecostomus in Venezuela and Clarias batrachus in the Far East. All of these are based on the
“nest stimulus” or “receptacle
stimulus” techniques, which
induce the brood fish to spawn. An
essential pre requisite for this is the
gravid condition of the males and females during the natural
spawning season. It is always
advisable to introduce one or two
males fewer than females, since the
males are known to fight with each
other when they out number the females. Induction of spawning by simulating decisive natural environmental conditions. The method of controlled propagation
of common carp is based on this
technique. This technique is also
known as Dubisch method. Ponds
used for this purpose are termed
“Dubisch ponds. The decisive natural conditions to
bring about spawning in common
carp are as follows:
1. suitable water temperature (18°–
22°C), 2. grass-bottomed spawning ground,
3. water saturated with dissolved
oxygen,
4. slowly rising water level,
5. presence of the other sex, and
6. absence of other fishes, especially
carnivorous fishes. Spawning ponds with the above
characteristics and measuring 100– 1 000 m2 each can be easily prepared. As an alternative, a rice
patch can also be converted for this
purpose. A stable source of clean
filtered water is an essential
requirement, however. A spawning pond of this type is
constructed as follows. A ditch 2–3
m wide and 0.6–0.8 m deep is dug
adjacent to the main dyke of the
pond, to serve as a refuge for the
breeders. A draining structure is then placed at one end of this
ditch. The other parts of the pond
are made to slope slightly toward
the ditch and are covered with
short grass. When the pond is fully
inundated, about 30–50 cm water will cover the grassy area . When the water temperature and
weather conditions are suitable,
one or two sets of spawners, each
set consisting of 2 females and 3
males, are introduced into the
inundated ditch. They are kept there for a few days, during which
period a gentle continuous flow of
water is maintained in the pond by
regulating the draining structure.
The draining exit is then closed and
more filtered water is drawn into the pond bringing about a slow
rise in water level. The rising water
gradually inundates the grassy
area. This operation triggers the
breeders into vigorous spawning.
A day after the spawning, the fish are carefully netted out
from the pond This removal
serves to prevent cannibalism and
the infection of the offspring by
parasites from the parent fish. This technique has also been
successfully employed to breed
some of the other fishes, such as
pike, tench, crucian carp, buffalo
fish, Puntius spp., etc. It should be possible to adopt this technique for
the induced breeding of any pond-
spawning fish that may be selected
for culture. 4.3.3.2 Induction of ovulation and spawning. Induced ovulation and spawning achieved through
hypophysation amounts to a
“short cut” of the natural
process. In nature, ovulation in a
fish is regulated and brought about
by its own gonadotropic hormone (s), produced and stored by the
pituitary gland. The stored
hormone is released into the blood
when all the requisite conditions
become favourable. But in the
hypophysation technique, gonadotropic hormone extracted
from the pituitary of some other
fish (donor) is injected into the
breeder and this brings about the
final ovulation. General considerations. Hypophysation is presently the
most commonly used technique for
the artificial propagation of fish. It
is employed not only in
propagation experiments, but also
in the commercial production of millions of young fish. Like all other techniques, this
technique too has its own
limitations. Some of the sensitive
fish such as the pike-perch cannot
tolerate the treatment, while
others may ovulate only irregularly. Then again, the
breeders whose ovaries have not
yet reached the adequately ripe
stage fail to respond to
hypophysation. It is a fundamental
rule that hypophysation will be effective only when the eggs in the
ovary have reached the resting or
dormant phase after the
completion of vitellogenesis. The
eggs are then materially ready for
further development to be triggered by gonadotropin(s). Pituitary glands of donor fishes,
collected fresh or preserved, are
used in hypophysation. It is
necessary that these glands contain
an adequate amount of stored
gonadotropic hormones to bring about successful spawning. The pituitary gland (hypophysis)
acts as an intermediary between
the brain and the gonads. Its cells
produce and store gonadotropins,
and release them only when the
gland receives the necessary command. The gonadotropin
content of the pituitary gland
varies during different seasons and
during different stages in the life of
the fish. Immature fishes have only
a small quantity of gonadotropin in their pituitary, while after natural
spawning the spent fish are
completely bereft of
gonadotropins in their pituitary.
On the other hand, the
gonadotropin content is at its highest level in the pituitary of
sexually ripe fishes when their
gonads have reached or nearly
reached the resting phase and
throughout the duration of the
resting phase. Since spawning migration is also triggered by
gonadotropin, the pituitary of such
migrating fish has a lower level of
gonadotropin content. In view of
these varying contents of
gonadotropin, it is important to choose the right time for collecting
the pituitary glands. Dosage. During natural ovulation, the fish is able to precisely regulate
the dosage of its own hormone.
Hence, there is no wastage. In the
case of hypophysation technique,
where in hormone from an external
source is injected, there is usually considerable wastage. This is
mainly because it is difficult to fix
the exact dosage, with the result
that generally more hormone than
required is injected into the
breeders. Ovulation is a complicated process
lasting several hours, with its exact
duration depending on
temperature. It is possible to
differentiate ovulation into 2
phases, viz., preovulation and ovulation. In the pre ovulation
phase, the migration of the nucleus
is completed and the egg absorbs a
large quantity of fluid (hydration).
Its size now is nearly the same as
its final size at ovulation. If hypophysation is unsuccessful, the
eggs stop developing at this phase
and the breeder may easily die due
to the necrosis of eggs which may
cause internal poisoning. The hormone dosage required can
vary significantly from fish to fish
of the same species and from
technique to technique. The dosage
actually depends on the
“readiness” of the females; their age, size, sensitivity and many
other factors. In tropical and
subtropical areas where the
metabolism of fish is far higher
(due to higher temperature) and
where the probability of wastage of hormone is, therefore, greater
than in temperate regions, usually
two or more doses are
administered. Generally, two doses
are given: the introductory or
preparatory dose, and the decisive or final dose. A single, full (100 percent) or
knock-out dose is given when the
breeder has been in the resting
phase for a long time. The
preparatory dose is about 10
percent of the total dose. If a further preparatory dose is to be
administered, again only 10
percent of the total dose is given.
Generally, for a total dose, about
2.5–3 mg (1 gland) of hypophysis
would be required per kg weight in the case of large breeders
weighing over 5 kg; 1.5 mg (0.5
gland) for medium sized fishes (2–
5 kg); and 0.75 mg (0.25 gland) for
small fishes (0.5–2 kg). It is
advisable to avoid over dose in preparatory injection, since it may
lead to partial ovulation, there by
upsetting the normal schedule. Between the preparatory and
decisive doses, there must be a
minimum lapse of 14 hours. The
maximum lapse is 24 hours, but
very rarely can it extent to 48
hours. When more than one preparatory dose is required, there
should be a span of 24 hours
between doses. The males, as a rule, are only given
one dose of hormone, usually at
the time when the females are
given the last decisive dose. It is
important that the males are not
administered the hormone earlier, since that may result in releasing
the sperm before the females are
ready to ovulate. The dosage of gonadotropin
hormone extract is expressed
either in milligrammes or as a
number of acetone-dried
hypophysis glands. The acetone-
dried pituitary gland of a 1.5–2 kg common carp, weighs 2.5–3 mg.
This size of hypophysis is taken as
a unit, when the dosage is
expressed in terms of number of
glands. The “gland unit” is easy to use.
Glands of approximately the same
size are taken for preparing the
dose. The other method of
calculating the dosage by weight is
more difficult, but is certainly more precise. A little excess hormone in the
decisive dose does not harm the
fish. An over dose of 10–15 percent
is generally given to be on the
safer side. For the total, or 100
percent dose, usually 1 to 1.5 glands (i.e. 3.0–4.5 mg) of
hypophysis are administered per
kg weight of the female. If the
calculated dose requires more than
five glands, one more gland is
usually added “for the mortar”. If the pituitary gland is available in
already pulverized form, a good
balance or a spoon of known
volume would be required to
measure the exact dosage. The dry
pituitary marketed in pulverized form can be easily adulterated with
brain tissue. Therefore, it is
advisable that the farmer buy his
hypophysis only from reliable
sources. The recommended single decisive
dose for males is 0.5 gland (1.0–1.5
mg) per kg of body weight
regardless of their length.
However, there is no need to
administer hormone to males found to be oozing milt. It is always advisable to be a little
liberal while calculating the
decisive dose. Hence, farmers are
advised to increase the required
dosage by 10–15 percent. A
principle to follow in practice is not to administer too much of
hormone in the preparatory dose
and too little in the decisive dose. When the decisive dose is
administered in two or three parts,
the time lapse between the
injections should not be more than
6–8 hours. Methods of hormone administration. There are several variations in hormone
administration methods. Each
method may have some
justification, but may not be
universally applicable. The
technique adopted is generally dependent on the species of fish,
local conditions, and working
methods developed by the local
scientists and technicians .
However, none can be proclaimed
as the only definitive technique. As a rule, the females generally
require higher doses of hormone
than the males, with split doses
producing better results than a
single large dose. The different methods of hormone
administration, as generally
practised, are detailed below. Single injection method. The calculated 100 percent dose, or the
knock-out dose, is given in a single
injection. It will be successful only if
the female is other wise fully ready
for spawning, as those that are in
their spawning migration or are captured on the spawning ground.
Suitably fed fishes achieve this
condition during the second half of
the breeding season. Among the majority of fish species,
males are better prepared for
spawning than females and,
there fore, a single dose suffices. If
the hormone administered to them
amounts to an overdose, or is not synchronized with the gonad al
maturation of the females, it may
result in the wild discharge of milt
before the females are ready. Preparatory and decisive doses method. The preparatory dose, which is about 10 percent of the
decisive dose, advances the
gonadal development up to the
pre ovulation stage. It is generally
given about 18–24 hours prior to
the decisive dose (100 percent of the calculated dose). This is a
generally successful sequence of
hormone administration in the
temperate and sub tropical regions.
This method also holds good for
nervous and difficult-to-handle fish. Sometimes the interval between
the preparatory and decisive doses
can be shorter than that indicated
above. About 14–18 hours suffice
during the latter half of the
spawning season, given that the water temperature is higher than
the normal spawning temperature.
If the females are less than 1 kg in
weight and are in ripe condition for
hormone treatment, an interval of
only 6 hours is sufficient. (a) One preparatory and two decisive doses In tropical regions, where the
metabolism in fish is more rapid,
the decisive dose is given in two
equal instalments or two
instalments of 40 percent and 60
percent, with an interval of 6–8 hours.

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