poor fish vs stupid person

poor fish and stupid person both are nouns.

Word	Noun	Adjective	Verb	Adverb
poor fish	Yes	No	No	No
stupid person	Yes	No	No	No

As nouns, poor fish and stupid person are synonyms defined as:

Other synonyms of poor fish include dolt, dullard, pillock, pudden-head, pudding head, stupe, stupid.

poor fish (noun)	stupid person (noun)
a person who is not very bright	a person who is not very bright