Freshwater

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Part II: Fish and How to Care for Them
Make sure that your tank is large enough to provide ample swimming room
for your aquatic friends.
When moving fish from one location to another, you must remember that gills
are made out of fine tissue that can collapse if removed from water. The gills
are structurally supported by the weight of the water itself. So it is very
important that you keep your fish in water while moving them, to avoid causing
any damage to their gills, bodies, and fins which can be crushed by lack
of water support.
The labyrinth organ method
A certain group of fishes (known as the Anabantids), found in Asia and Africa,
are able to breathe air directly from the atmosphere, using a specialized
organ called the labyrinth. The labyrinth, located inside the head behind the
gills, has evolved over time to take oxygen directly from the air as a supplement
to extracting it from the water.
Anabantids include bettas, gouramis, and paradise fish. In the wild, many of
these fish live in dirty, poorly oxygenated waters full of strange-looking creatures.
(Not unlike a good day at our public pool.) These fish tend to have
wide bodies and enlarged fins.
The physical shape of the labyrinth organ gives rise to its name, which literally
means “maze.” The labyrinth contains rosette-shaped plates that have
thousands of oxygen-absorbing blood vessels, which gather air that is
inhaled. The inhaled air is then trapped inside a group of folds (which resembles
a sponge) and is eventually absorbed into the main bloodstream.
Anabantids can survive in a smaller aquarium space than that which is normally
provided (usually 10 or more gallons) because they can extract oxygen
from the air. However, this does not mean that anabantids can or should be
kept in very crowded conditions or extremely tiny tanks. Even though they
have the ability to breathe “extra” air, these fishes still add as much waste to
the water as their tankmates and need proper space and filtration for healthy
living.
You will often see betta fish for sale in small jars. The reason many dealers do
this is to keep the males separated so that they don’t fight. This is not a good
practice for the home aquartist to pick up and use. Don’t keep labyrinth fish
in small bowls or hanging vases for decoration purposes. Give them a good
healthy aquarium environment with plenty of room instead.