Fish in small trap, wriggling (5)
I believe the answer is:
sprat
'fish' is the definition.
(sprat is a kind of fish)
'small trap wriggling' is the wordplay.
'small' becomes 's' (abbreviation - e.g. clothes size**).
'wriggling' indicates anagramming the letters.
'trap' with letters rearranged gives 'prat'.
's'+'prat'='SPRAT'
'in' is the link.
(Other definitions for sprat that I've seen before include "Parts of a very small fish" , "It's set to catch a mackerel" , "Herring of the east North Atlantic" , "little fish" , "chap on a fat-free diet" .)