Fish swimming around? Only a little (3)
I believe the answer is:
gar
'fish' is the definition.
(gar is a kind of fish)
'swimming around? only a little' is the wordplay.
'only a little' indicates a hidden word.
'GAR' is hidden in the letters of 'swimming around'.
(Other definitions for gar that I've seen before include "swimmer" , "Pike-like fish" , "A fish; cloth scrap (reversed)" , "Type of fish" , "Creature" .)