Page 68 - Encyclopedia of Aquarium and Pond Fish, 3rd Edition

66 FRESHWATER FISH: BREEDING

to 90°F (32°C). The disadvantage of speeding up gestation is
that higher temperatures also quicken the rest of the life cycle
of the fish, thus shortening their life span.
Although most livebearers produce offspring readily, even in
a community tank, few of the fry survive to adulthood because
they are eagerly devoured by other tank occupants— often
including their own mother. To avoid this unnecessary carnage,
you can transfer the pregnant female to a breeding trap, or
spawning box. The breeding trap, which hooks over the side of
the tank or floats freely in the water, has a birthing chamber
that houses the female. Small holes or slits in the
floor or walls of the chamber allow
newborn fry to escape into a secondary
Breeding traps protect newborn The lower chamber, where they can develop in
livebearers from their mother and chamber safety, out of reach of the female and
other tank occupants. In the trap protects the separate from the main tank. Once they
fry from
above, the mother rests in the top being eaten
section, while the fry slip through have grown too large to be eaten, the fry
a slit in the floor into the lower Air trapped under each can be released into the main aquarium.
chamber. The trap on the right has end provides buoyancy Avoid buying small breeding traps, since
a double birthing chamber, Slits in the floor of the birthing
to house two pregnant females. chamber allow fry to pass through gravid females will become distressed if they are
confined in too small a space. Do not wait until
spawning can be triggered by making a partial water change immediately before the birth before transferring the female,
and dropping the water temperature slightly. Feeding extra since this is likely to cause her to abort her brood. The ideal
live foods will also help, since invertebrates naturally become time to move her is about a week before the brood is due.
more numerous in the floodwaters at this time. In contrast,
annual killifish can be brought into breeding condition by
lowering the water level and slightly increasing the
temperature, since in the wild they spawn when the sun NEWLY HATCHED FRY
begins to dry up the pools in which they naturally live. After hatching, a young fish is initially sustained by nutrients in the
It is usually possible to tell from the changing appearance remains of its yolk sac, which attaches to the underside of the fish’s
and behavior of the fish that spawning is imminent. The males body. In this picture of Arawana fry (see p.182), the yolk sacs are the
may take on a more intense breeding coloration and show reddish-orange “bags” dangling beneath the fish. Only when the
yolk sac has been fully absorbed will a fish start to swim around the
aggression toward one another. They will actively pursue aquarium actively seeking food. Until that time, it rests on the floor
the females, whose body becomes swollen with developing of the tank or elsewhere out of sight. The fry that emerge from the
eggs. In some species, you may also notice that the fish eggs are usually tiny replicas of the adult fish. In a few species, such
perform courtship rituals or carefully clean spawning sites, as discus, the young have a body shape very different from their
such as rocks or leaves. This is the time to transfer the fish to parents’ but come to resemble them as they increase in size.
a spawning tank (see p.65). In territorial species that spawn in
pairs or small groups, always move the females first to allow
them to settle in the tank before the males are introduced.
Communal spawners can be introduced as a shoal.

Breeding livebearers
Livebearers need little encouragement to breed in aquariums.
Like egg-layers, they benefit from protein-rich conditioning
foods, but many originate from relatively stable habitats and
are not seasonal spawners, so they do not need environmental
changes to trigger spawning. The water temperature does,
however, influence the gestation period. For example, at
77°F (25°C), gestation in guppies takes 28 days, but this
figure falls to just 19 days when the temperature is raised

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