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Breeding Egg layers
Separate male and female hormones are produced in fishes. During spawning period
the female releases eggs in the water and the male simultaneously release milt close
to the eggs. The eggs are thus fertilized outside the body of the female (external
fertilization). Based on the type of incubation egg laying fishes are further classified
into five
Egg scatterers laying non-adhesive
eggs
Egg scatterers laying adhesive eggs
Egg depositors
Egg buriers
Nest builders
Egg scatterers laying non-adhesive eggs
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Zebra fish (Danio spp.) is considered as egg scatterer, which lays non-adhesive
eggs. Like many aquarium fishes, zebra fish also eats away its own eggs and spawn
after breeding. As the precautionary measure, the bottom of the aquarium should
be loaded with a layer of round pebbles of about 6-8 cm diameter. The breeding pair
has to be well fed with live food like small zooplanktons.
During breeding the male female ration should be maintained at 2:1 or 3:1. The female
is introduced in the breeding tank one day earlier than the males. The eggs require
2-3 days hatching time, if the temperature is favourable. As soon as the tiny hatchlings
are seen in the aquarium tanks the parents are to be removed. The hatchlings take
2 days to absorb their yellow yolk sac. After 2 days, they are fed with infusorians
for 4 days. Subsequently rotifers and smaller zooplanktons can be fed for 1 week,
after which they can be provided with powdered formulate feed.
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Egg scatterers laying adhesive eggs
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Gold fish (Carassius spp.) is considered as egg scatterer laying adhesive
eggs. When secondary sexual characters appear, the male and female gold fishes are
selected and kept in circular glass tanks (24’’x 12’’x 15’’)
or ferro-cement tank (3.5 ft. x 2.5 ft.) after disinfecting the containers with
1 ppm solution of potassium permanganate. The water used should be a mixture of
ground and filtered pond water. The tanks should be placed where some early morning
sunshine and no sunlight afterwards fall. Since goldfish eggs are sticky in nature,
they require a surface to adhere. For this various artificial nets or submerged
aquatic plants such as Hydrilla can be used. The nets should float close
to the surface of water. The water temperature should be maintained between 20o
and 30o C.
The spawner and milter in the ratio of 1:2 are released into the breeding tank in
the late evening hours. Egg laying usually takes place within 6-12 hrs. The moment
spawning is over nets should be transferred to a different container, or parent
fishes are removed from the breeding tank. Generally a female lays about 2000- 3000
eggs. Healthy eggs are golden transparent at the beginning and gradually the transparency
decreases. Unfertilized eggs will remain opaque. Under ideal condition, within 3
days, the eggs hatch-out with a hatching rate of 80-90%. When the young larvae start
to float the nets and aquarium plants can be removed.
Barbs (Rasbora spp.), small fishes that move in groups are ideal for a
well-planted community aquarium. A temperature between 25° and 28° C is
optimum for their breeding. They are difficult to breed but can lay up to 250 eggs/female.
Like barbs they require soft, slightly acidic (pH 5.5) environment. After conditioning
male and female are placed in a tank planted with flat leaved plants. Once spawning
occurs, as indicated by the sliminess of the female fish, remove both parents from
the breeding tank. The eggs laid on the underside of the flat levels will hatch
after 24-36 hr and the resultant hatchlings become free swimming after 3-5 days.
At this stage the tiny hatchlings should be fed infusorians and newly hatched brine
shrimp. As they grow bigger they should be fed zooplanktons, like Moina
and Daphnia.
Among the egg buriers, the killi fish (Aplocheilus spp.) is the most important.
They lay their eggs in a soft peat at the bottom of the tank or in densely planted
aquarium tanks. They are good jumpers; therefore, they should be kept in covered
aquarium. The eggs are capable of remaining viable even under dried condition and
hatching may be possible even after some weeks or months, when placed again in water.
In drought condition, parents may die but their eggs remain alive until the next
rain. They rarely grow up to 3-4 cm in total length and are short lived.
The common nest builders are Gourami, Siamese fighter and Angelfish. They are bubble
nest builders and incubate their eggs in floating nests, specially made by the male
fish.
- Gourami (Osphronemus spp.):
Among the nest builders gouramis are the most popular. For breeding purposes
males and females are kept separately in different tanks for a week and fed with
live food. When the abdomen of female becomes grossly, distended with eggs it is
transferred to a smaller breeding tank with water level of 5-6” at 28o-30o
C. The tank should contain plenty of fine-leaf plants such as Cabomba and
some floating plants. The water hardness of 100-200 ppm and pH of 7.0-7.5 are ideal.
After 1-2 days, mature male is introduced in the breeding
tank. A transparent perforated plastic sheet or a glass is covered over the tank
to keep the humidity and temperature at high level, which help to maintain the bubble
nest in good condition. The male soon begins to build the bubble nest. This is possible
by engulfing a large gulp of air at the water surface and converting it into many
smaller bubbles that are passed into gill chamber and coated with an anti-burst
agent before release.
After making the nest, the female deposits a large number of eggs in the nest. After
breeding, female is removed, while males guard the nest. Hatching takes place within
24-36 hr and the moment fry swim freely from the nest, males are removed from the
tank. The young ones are given infusorians at this stage and after a week newly
hatched artemia and small cladocerans are provided. As they grow they accept all
kinds of prepared feeds.
- Siamese fighter (Betta splendens):
Adult fish attain sexual dimorphism at a length of 6 cm. It is best to attempt breeding
with fishes that are about 9-12 months old. Allow one male to every 2 or 3 females.
Females should be at least the same size as the male. Males are kept in small aquaria
of 2-5 litre capacity, while females are kept in tanks containing 25-50 litres of
water. Another breeding tank containing 50 litres water (depth 15 cm) and having
leaf plants like Myriophyllum and Cabomba, is required. The tank
has to be partitioned into two using fine mesh net. In one half females and other
half male fish is placed. Water temperature is maintained around 27°C.
The male starts building a bubble nest quite quickly and once this is underway,
the partition net is removed. At this crucial stage male should accept the female,
otherwise male starts vigorous display of chasing which ultimately leads to fin
tearing of female. Fighters often spawn in early morning and within a few hours
200-300 eggs are laid. As the eggs are shed and fertilized, they sink to the bottom.
Males then collect them in his mouth and spit them into the bubble nest. At the
end of spawning females are removed and male is left to guard the nest for 3 days
after which it is removed. The eggs hatch after 36-48 hr. The smaller fry become
free swimming after 5 or 6 days during when they can be fed with infusorium and
egg-yolk. After 3 or 4 days, frys generally accept fine dry foods. The temperature
of the water should be warm at around 27° C.
Bubblenest of siamese fighter
fish
- Angelfish (Pterophyllum spp.):
The mature angelfish having straight top and bottom fins without any bowing or bend
is selected. They should be healthy, strong, robust and active. Unfortunately it
is very difficult to differentiate between a male and female angelfish externally.
In the beginning, 6-8 potential breeders are selected which can be set in a 100-litre
tank and they are fed well with live food. The fish soon make pairs and start displaying
breeding and courtship behavior. They spawn on broad-leaved Amazon sword plants
in the aquarium. Angelfish prefer water with a 6.0–8.0 pH, with 6.5-7.4 being
ideal, a water hardness of 50–130 ppm, and a temperature range of 24–30°
C.
The female will deposit a line of eggs on the spawning substrate, followed by the
male who will fertilize the eggs. This process will repeat itself until there are
a total of 100-600 eggs. The pair will take turns maintaining a high rate of water
circulation around the eggs by swimming very close to the eggs and fanning the eggs
with their lateral fins. In a few days, the eggs will hatch and the fry will remain
attached to the spawning substrate. During this period, the fry will not eat and
will survive by consuming the remains of their yolk sacs. At one week, the fry will
detach and become free-swimming. Fry can now feed on brine shrimp and after 2 weeks
feed on powdered artificial feed.
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