An anadromous fish, born in fresh water, spends
most of its life in the sea and returns to fresh water to spawn. Salmon,
smelt, shad, striped bass, and sturgeon
are common examples.
A catadromous fish does the opposite - lives in
fresh water and enters salt water to spawn. Most of the eels are
Why do scientists classify fish?
Since common or colloquial names of fish vary from place to
place (menhaden, for example, are known by at least three different
names, and striped bass are called "stripers" in New England and "rockfish" in Chesapeake Bay),
investigators would have no way of
differentiating among species without a uniform naming system. The
system used to name the 20,000 odd fishes known to science is called
"the binomial system of nomenclature." It usually consists of a
scientific name in two parts, the generic and specific names, or three
parts if subspecies have been described.
The words of the names are
latinized regardless of the language or alphabet of the study and are
frequently descriptive of a significant feature of the organism.
The generic name generally applies to several species showing basic
characteristics while a specific (species) name is based on a few
characteristics applying to one species, separate and distinct from all
others. (Example: The generic name Morone applies to white perch,
white bass, and striped bass; the species names for those three fishes
are Morone americanus, M. chrysops, and M. saxatilis.)
Mainly by two methods: Growth "rings" on scales, and/or
ringlike structures found in otoliths (small bones of the inner ear),
are examined and counted. The rings correspond to seasonal changes in
the environment and can be compared to the annual rings of tree trunks.
A series of fine rings are laid down in scales for each year of life in
summer, the rings grow faster and have relatively wide separations; in
winter, slower growth is indicated by narrow separations between
rings. Each pair of rings indicates one year. Because scale rings are
sometimes influenced by other factors, scientists often use otoliths,
whose ringlike structures also indicate years of life.
A few weeks or months (some of the small reef fishes) to
50 years or more (sturgeons)
Longevity information is still sparse, but scientists have learned that
species live 10 to 20 years in temperate waters.
Yes, many do. These are called viviparous fishes. The sea
perches of the Pacific coast, for example, give birth to living young
of considerable size, sometimes one-fifth the size of the mother.
Several kind of sharks produce living young