Greek character managed a laugh for fish (7)
I believe the answer is:
piranha
'for fish' is the definition.
(piranha is a kind of fish)
'greek character managed a laugh' is the wordplay.
'greek character' becomes 'pi' (letter from the Greek alphabet).
'managed' becomes 'ran' (both can mean organised or was in charge of).
'a laugh' becomes 'ha'.
'pi'+'ran'+'ha'='PIRANHA'
(Other definitions for piranha that I've seen before include "This predator" , "Small voracious carnivorous fish" , "Efficient flesh remover" , "fish chewed up" , "Small carnivorous freshwater fish" .)