Fishy figure not generous about room (6)
I believe the answer is:
merman
'fishy figure' is the definition.
The answer and definition can be both people as well as being singular nouns.
Maybe there's a link between them I don't understand?
'not generous about room' is the wordplay.
'not generous' becomes 'mean' (I can't explain this - if you can you should believe this answer much more).
'about' means one lot of letters goes inside another.
'room' becomes 'rm' (abbreviation).
'mean' going around 'rm' is 'MERMAN'.
Can you help me to learn more?
(Other definitions for merman that I've seen before include "Ethel --, singer" , "fishy character" , "Fabulous creature" , "Half man, half fish" .)