Fish with many an expert (4)
I believe the answer is:
dace
'fish' is the definition.
(dace is a kind of fish)
'with many an expert' is the wordplay.
'with' is a charade indicator (letters next to each other).
'many' becomes 'd' (**).
'an expert' becomes 'ace' (ace is a kind of expert).
'd' next to 'ace' is 'DACE'.
(Other definitions for dace that I've seen before include "Small river fish" , "Chubby swimmer" , "Freshwater fish" , "Fish in the carp family" .)