Migrating Fish
Many species of fish do reproduce in freshwater, but spend most of their adult lives in the sea. These are known as anadromous fish, and include, for instance, salmon, trout and three-spined stickleback. Some other kinds of fish are, on the contrary, born in salt water, but live most of or parts of their adult lives in fresh water; for instance the eels. These are known as catadromous fish.
Species migrating between marine and fresh waters need adaptations for both environments; when in salt water they need to keep the bodily salt concentration on a level lower than the surroundings, and vice versa. Many species solve this problem by associating different habitats with different stages of life. Both eels, anadromous salmoniform fish and the sea lamprey have different tolerances in salinity in different stages of their lives.
Read more about this topic: Freshwater Fish
Famous quotes containing the words migrating and/or fish:
“It is as when a migrating army of mice girdles a forest of pines. The chopper fells trees from the same motive that the mouse gnaws them,—to get his living. You tell me that he has a more interesting family than the mouse. That is as it happens.”
—Henry David Thoreau (1817–1862)
“Until they saw, over the mists
of Venus, two fish creatures stop
on spangled legs and crawl
from the belly of the sea.
And from the planet park
they heard the new fruit drop.”
—Anne Sexton (1928–1974)