Fish finally landed by expert (4)
I believe the answer is:
dace
'fish' is the definition.
(dace is a kind of fish)
'finally landed by expert' is the wordplay.
'finally' indicates one should take the final letters.
'by' means one lot of letters go next to another.
'expert' becomes 'ace' (ace can informally mean very good).
The final letter of 'landed' is 'd'.
'd'+'ace'='DACE'
(Other definitions for dace that I've seen before include "Fish in the carp family" , "Freshwater fish" , "Small river fish" , "Chubby swimmer" .)