Last part of fish Alan halved (5)
I believe the answer is:
final
'last' is the definition.
(I know that last can be written as final)
'part of fish alan halved' is the wordplay.
'part of fish' becomes 'fin' (fish have fins).
'halved' means to take half the letters.
'alan' cut in half is 'al'.
'fin'+'al'='FINAL'
(Other definitions for final that I've seen before include "Like one's journey to cemetery" , "Concluding" , "Conclusive" , "Coming at the end" , "Last in a series of games or contests" .)