Immature frogs (8)
I believe the answer is:
tadpoles
'immature frogs' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for tadpoles that I've seen before include "Little swimmers" , "Larvae of frogs or toads" , "Baby frogs" , "Stop deal (anag.)" , "Pond-life" .)