Unexpected fish, a lone catch at sea (10)

I believe the answer is:

coelacanth

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

'unexpected fish' is the definition.
'coelacanth' can be an answer for 'fish' (coelacanth is a kind of fish). I am unsure of the 'unexpected' bit.

'a lone catch at sea' is the wordplay.
'at sea' indicates an anagram.
'a'+'lone'+'catch'='alonecatch'
'alonecatch' anagrammed gives 'COELACANTH'.

Can you help me to learn more?

(Another definition for coelacanth that I've seen is " bony fish".)

I've seen this clue in The Times.

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