Little Benjamin holds large fish (6)
I believe the answer is:
blenny
'fish' is the definition.
(blenny is a kind of fish)
'little benjamin holds large' is the wordplay.
'little' becomes 'l' (abbreviation).
'benjamin' becomes 'ben' (short for Benjamin).
'holds' means one lot of letters goes inside another.
'large' becomes 'ny' (I can't justify this - if you can you should give a lot more credence to this answer).
'l' inserted into 'ben' is 'blen'.
'blen'+'ny'='BLENNY'
Can you help me to learn more?
(Other definitions for blenny that I've seen before include "Spiny-finned fish" , "slimy fish" .)