Crossword Genius

Chicken an unfit alternative for fish (9,4)

Ross

I believe the answer is:

yellowfin tuna

I'm a little stuck... Click here to teach me more about this clue!

'fish' is the definition.
The answer and definition can be both animals as well as being singular nouns.
Maybe they are linked in a way I don't understand?

'chicken an unfit alternative' is the wordplay.
'chicken' becomes 'yellow' (as in cowardly).
'alternative' is an anagram indicator (an alternative ordering of the letters).
'an'+'unfit'='anunfit'
'anunfit' is an anagram of 'fintuna'.
'yellow'+'fintuna'='YELLOWFIN TUNA'

'for' is the link.

Can you help me to learn more?

I've seen this clue in The Irish Times.
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