Physical Characteristics
Most species possess a swim bladder (except in Gonorynchus). The swim bladder is usually divided into two chambers. A smaller anterior chamber is partially or completely covered by a silvery peritoneal tunic. A larger posterior chamber may be reduced or absent in some groups. Minute, unicellular, horny projections known as "unculi" are commonly present on various body parts and are only known from ostariophysians.
Many ostariophysians have the characteristic of an alarm substance that is part of a fright reaction. This is a pheromone produced in epidermal club cells, and is similar or identical in all ostariophysians. When the fish is injured, this pheromone is released; other fish of the same species or similar species can smell this pheromone, causing a fright reaction. However, some fish possess the alarm substance without the fright reaction or lack both the alarm substance and the fright reaction to the alarm substance.
Read more about this topic: Ostariophysi
Famous quotes containing the word physical:
“The axioms of physics translate the laws of ethics. Thus, “the whole is greater than its part;” “reaction is equal to action;” “the smallest weight may be made to lift the greatest, the difference of weight being compensated by time;” and many the like propositions, which have an ethical as well as physical sense. These propositions have a much more extensive and universal sense when applied to human life, than when confined to technical use.”
—Ralph Waldo Emerson (1803–1882)