alevin
Young salmon that have hatched but still have a large yolk that must be absorbed, during which they stay protected in gravel; they may live entirely on yolk or may feed (may also be called "sac-fry").

anadromous
(Greek for "running upward") Fish that are born in fresh water, move to salt water to feed, and return to fresh water to spawn.

catadromous
Fish that are born in salt water, move to fresh water to feed, and return to salt water to spawn.

diadromous
Fish that can live in fresh and salt water, at different times in their lives.

estuary
A site where fresh water and salt water meet.*

fish ladder
Water-filled staircase that allows migrating fish to swim upstream around a dam.*

fry
Next life stage of salmon after alevin, and before smolt (upon reaching 1.25 inches in length, they are sometimes called "fingerlings") (see also "parr").

gill
Respiratory organ of fish.

homing
The behavior of returning to the stream where you were hatched.

iteroparous
Spawn more than once.

opercula
The gill covers of a fish.

parr
Stripes on the sides of salmon fry; sometimes used instead of "fry" to refer to juvenile salmon.

redd
Series of nests dug in gravel by one female salmon.

semelparous
Spawn only once during their lifetime.

smolt
Salmon of a certain size, generally 4-7 inches, that begin seaward migration and smoltification.

smoltification
Process of morphological and physiological adjustment that young salmon of a certain size undergo to live in salt water.

spawning
The act of laying eggs.

* Indicates definitions adapted from Project WILD Aquatic Education Activity Guide, 1992