Fish from barrel, nearly empty (5)
I believe the answer is:
tunny
'fish' is the definition.
(tunny is a kind of fish)
'barrel nearly empty' is the wordplay.
'barrel' becomes 'tun' (tun is a kind of barrel).
'empty' suggests removing the centre.
'nearly' with its centre removed is 'ny'.
'tun'+'ny'='TUNNY'
'from' is the link.
(Other definitions for tunny that I've seen before include "Large marine fish" , "Marine fish, the bluefin" , "Warm water food fish" , "Common food fish" , "A tuna" .)