Broadly stated, a fish is a cold-blooded vertebrate
(an animal with a backbone) which lives in water, and usually possesses
paired fins, gills, and scales.
Most of the fishes in this taxon that are familiar to us belong to the
class Osteichthyes, Bony Fishes. They are characterized from other fishes
by having a skeleton that is reinforced by a hard matrix of calcium phosphate.
How Does a Fish Breathe?
Most fish breathe by drawing water over four or five pairs of gills
that are located in chambers covered by a protective flap, the operculum.
This enables the fish to breath while stationary; sharks lack operculi
and must move to pass water over the gills. Some fish breathe air while
a few may even absorb air through their skin if they lack scales.
Reproduction
Details in reproduction of bony fishes vary extensively. Most species
are oviparous, reproducing by external fertilization after the female
sheds large numbers of small eggs. However, internal fertilization and
live birth characterize other species. Some bony fishes display complex
mating rituals.
Skin
The skin of bony fishes is often covered by flattened bony scales that
differ in structure from the toothlike scales of sharks. Glands in the
skin of a bony fish secrete a mucus that gives the animal its characteristic
sliminess, an adaptation that reduces drag during swimming and acts as
a barrier to infections.
The Swim Bladder
Another adaptation of most bony fishes not found in sharks is the swim
bladder, an air sac that helps control the buoyancy of the fish. Bony
fishes are generally maneuverable swimmers, their flexible fins better
for steering and propulsion than the stiffer fins of sharks.
Endangered Species
Several distinct classes of bony fish evolved by the end of the Devonian
period: the ray-finned fishes and the fleshy-finned fishes. Nearly all
the families of fishes familiar to us are ray-fins.
One species of particular concern in the Thompson-Okanagan region belongs
to the Minnows, Family CYPRINIDAE. This family is composed of a great
number of fishes, usually of small size. They have no adipose fin or teeth
in the mouth. Instead, they have well-developed "pharyngeal"
teeth in the throat.
The Chiselmouth (Acrocheilus
alutaceus), of the family CYPRINIDAE, is one example
of a species found in only a few rivers and lakes of the Thompson-Okanagan
region of southern British Columbia.
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