Visual artist capturing head of turbot, a large fish (5,3)
I believe the answer is:
manta ray
'large fish' is the definition.
(I've seen this before)
'visual artist capturing head of turbot a' is the wordplay.
'visual artist' becomes 'manray' (visual artist Man Ray).
'capturing' indicates putting letters inside.
'head of' indicates taking the first letters.
The initial letter of 'turbot' is 't'.
't'+'a'='ta'
'manray' going around 'ta' is 'MANTA RAY'.
(Other definitions for manta ray that I've seen before include "large fish" , "Devilfish" .)