rainbow smelt vs American smelt

rainbow smelt and American smelt both are nouns.

Word	Noun	Adjective	Verb	Adverb
rainbow smelt	Yes	No	No	No
American smelt	Yes	No	No	No

As nouns, rainbow smelt and American smelt are synonyms defined as:

rainbow smelt and American smelt: common smelt of eastern North America and Alaska

rainbow smelt (noun)	American smelt (noun)
important marine and landlocked food fish of eastern North America and Alaska	common smelt of eastern North America and Alaska
common smelt of eastern North America and Alaska