Spinning reel's catching very young fish (5)
I believe the answer is:
elver
'young fish' is the definition.
(I've seen this before)
'spinning reel's catching very' is the wordplay.
'spinning' indicates an anagram.
'catching' indicates putting letters inside.
'very' becomes 'v' (common abbreviation).
'reel' with letters rearranged gives 'eler'.
'eler' placed around 'v' is 'ELVER'.
(Other definitions for elver that I've seen before include "One may see one upriver" , "Young migratory fish" , "slippery little thing" , "A young 11" , "New slipper" .)