Crossword Genius

Various kinds of fish in large cask, as follows (5)

Ross

I believe the answer is:

tunas

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'various kinds of fish' is the definition.
I can't judge whether this defines the answer.

'large cask as follows' is the wordplay.
'large cask' becomes 'tun' (type of container for alcohol).
'follows' is a charade indicator (letters next to each other).
'tun'+'as'='TUNAS'

'in' acts as a link.

Can you help me to learn more?

(Other definitions for tunas that I've seen before include "pears? Exotic, perhaps" , "Two kinds of fish" .)

I've seen this clue in The Guardian.
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