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olfaction

Chemical sensory, similar to smelling, used by fish for many purposes including capturing prey and navigation. Trout and salmon use olfaction as one way of finding their natal streams to spawn.

opercle

A bony "flap" behind a fish's head that protects the gills.

organism

A living thing consisting of one or more cells.

An individual form of life, such as a plant, animal, bacterium, protist, or fungus; a body made up of organs, organelles, or other parts that work together to carry on the various processes of life.

A system regarded as analogous in its structure or functions to a living body: the social organism.