This fish looks and sounds flat? (6)
I believe the answer is:
plaice
'this fish looks' is the definition.
'plaice' can be an answer for 'fish' (plaice is a kind of fish). I am not sure about the remainder of the definition.
'sounds flat?' is the wordplay.
'sounds' shows a homophone (sound like).
'flat?' becomes 'place' (flat is a type of residence or place).
'place' is a homophone of 'PLAICE'.
'and' acts as a link.
(Other definitions for plaice that I've seen before include "Edible flatfish" , "Large flat fish" , "Large flatfish" , "A succulent flat-fish" , "Flat fare" .)