When a friend gets the last portion of fish (7)
I believe the answer is:
finally
'the last portion of fish' is the definition.
I can't judge whether this defines the answer.
'when a friend' is the wordplay.
'when' becomes 'fin' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'a friend' becomes 'ally' (an ally is a friend or supporter).
'fin'+'ally'='FINALLY'
'gets' acts as a link.
Can you help me to learn more?
(Other definitions for finally that I've seen before include "when all is said and done" , "for ever" , "At last" .)