Crossword Genius

No starter for Ruth, one eating fish (5)

Ross

I believe the answer is:

egret

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

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

I don't understand how the rest of the clue works.

Can you help me to learn more?

(Other definitions for egret that I've seen before include "White wading bird" , "One of a pair of waders" , "Wading bird like a heron" , "white fish eater" , "Greet (anag) -- wading bird" .)

I've seen this clue in The Sun.
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