sea trout vs Salmo trutta

sea trout and Salmo trutta both are nouns.

Word	Noun	Adjective	Verb	Adverb
sea trout	Yes	No	No	No
Salmo trutta	Yes	No	No	No

As nouns, Salmo trutta is a hypernym of sea trout; that is, Salmo trutta is a word with a broader meaning than sea trout:

sea trout: silvery marine variety of brown trout that migrates to fresh water to spawn
Salmo trutta: speckled trout of European rivers; introduced in North America

Other hypernyms of sea trout include brown trout, salmon trout.

sea trout (noun)	Salmo trutta (noun)
silvery marine variety of brown trout that migrates to fresh water to spawn	speckled trout of European rivers; introduced in North America
any of several sciaenid fishes of North American coastal waters
flesh of marine trout that migrate from salt to fresh water