Livebearers
Majority of people may be astonished upon learning that there are
commonly kept aquarium fishes that give birth to living young instead of
laying eggs. Giving live birth is usually associated with mammals and
the fact that some fish have develop this method, they are as well
considered to have mammalian traits. The truth is, many vertebrate
animals give birth to living young. These fish are called livebearers.
Among other aquarium fishes only one livebearing family
is well represented, the Poeciliidae. Together with this family belong
the less well-known Limias, and Guppies, Swordtails and Platies,
Gambusia and Mosquito Fish (Heterandria). There are several other
Poeciliidi, but are rarely found in aquarium shops because those that
are available are characterised by so many color varieties that fill the
market.
The benefit to an animal that reproduces by giving live birth instead of
laying eggs is so obvious. Because the offspring is already
well-developed and self-sufficient in ability to feed and move away from
any danger or threats. The new generation's survival is somewhat
less unsafe that it is for an egg or vulnerable larvae. The parent need
not produce as many young to insure survival for its kind and in return
the parent animal doesn’t need to expend as much energy and
food
material in producing many eggs or in building nests and caring
for the eggs and powerless young which hatch from them. This energy and
food can be used by the parent for its own needs to survive with only
less effort than if were obliged to cast a larger amount of its
substance as an egg-laying animal. Of course livebearing animals,
including fish don't know all this and have not chosen livebearing over
egg-laying as a more inexpensive method of reproduction, but the advantages are present nonetheless. That
many unrelated animals reproduce in this general way attests to its
effectiveness. While egg-laying fishes typically
produce hundreds or
thousands of eggs each spawning, livebearing fishes only generate few
dozen young at a time.
Keeping the eggs in the female body until the young are well developed
and able to swim directly after they are born reduces the number of eggs
necessary to replace the parent generation.
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