An organism that lives exclusively in salty or marine environments and cannot survive in freshwater.
From Greek 'halo-' (salt) plus 'biont' (from 'bios' meaning life, plus the agent suffix '-ont'). The term was coined in modern scientific taxonomy to describe organisms specifically adapted to salt water habitats.
Some fish are halobionts—they'll die if you put them in fresh water—while other fish are 'euryhaline,' meaning they can handle both salt and fresh water, which is why salmon are such incredible athletes (they literally change their body chemistry to switch habitats).
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