Small fish - the smallest present (6)
I believe the answer is:
minnow
'small fish' is the definition.
(I've seen this before)
'smallest present' is the wordplay.
'smallest' becomes 'min' (abbreviation for minimum).
'present' becomes 'now' (both can mean the current period).
'min'+'now'='MINNOW'
'the' acts as a link.
(Other definitions for minnow that I've seen before include "Very small freshwater fish of the carp family" , "Fish; underdog" , "Tiny freshwater fish" , "Very little fish" , "Small fry" .)