Fish caught on a river trip, finally (4)
I believe the answer is:
carp
'fish' is the definition.
(carp is a kind of fish)
'caught on a river trip finally' is the wordplay.
'caught' becomes 'c' (cricket abbreviation**).
'on' is a charade indicator (letters next to each other).
'finally' says to take the final letters.
The last letters of 'river trip' are 'rp'.
'c'+'a'+'rp'='CARP'
(Other definitions for carp that I've seen before include "Moan; fish" , "Complain continually" , "Nagging fish?" , "Fish often kept in ponds" , "praise? The opposite" .)