Buying an Aquarium for a Child or Teen in Melbourne Buying an Aquarium for Child or Teen in Melbourne | Page 17

In addition, fish often possess a characteristic organ, the air bladder. This is a long bag
filled with gas and lying in the body cavity. It may be entirely closed, or it may
communicate with the alimentary tract by means of a duct, or tube. Sometimes it is divided
into two rather distinct parts, which communicate with each other. The air bladder
controls the specific gravity of the fish, as the driving tanks of a submarine govern its
buoyancy, or vice versa really.
 Lateral Line
Upon careful examination of the majority of freshwater aquarium fish, a line may be
observed running from the head along the side of the body. This is a series of tubes filled
with a gummy secretion and with stiff bristles at the base. The function of this lateral line
is to direct vibrations of low frequency, and act as the fish’s ear, it is a specialized part of
the lateral line system to warn of danger, help with distance, sense obstacles that cannot be
easily seen and avoid predators.
 Nostrils
It may seem odd indeed that fish have what seem to be nostrils, but they do have nostrils
none the less. In fact, fish often have 4 nostrils. They are actually organs of smell and do
not perform any function in breathing, since they do not open to the mouth or gills.
9.0 Stocking Your Aquarium Evenly With the Correct Number of Fish