Gracious! An angel fish? (4,8)
I believe the answer is:
holy mackerel
'gracious an angel' is the definition.
The definition suggests a singular noun which matches the answer.
'fish?' is the wordplay.
I cannot quite understand how this works, but
'fish?' could be 'mackerel' (mackerel is a kind of fish) and 'mackerel' is present in the answer.
The remaining letters 'holy' is a valid word which might be clued in a way I don't see.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for holy mackerel that I've seen before include "Gosh!" , "Sacred fish (invoked in surprise)" .)