Fish and cask ale for starter? (4)
I believe the answer is:
tuna
'fish' is the definition.
(tuna is a type of fish)
'cask ale for starter?' is the wordplay.
'cask' becomes 'tun' (tun is a kind of cask).
'for starter?' suggests taking the first letters (I've seen 'for starters' mean this).
The initial letter of 'ale' is 'a'.
'tun'+'a'='TUNA'
'and' acts as a link.
(Other definitions for tuna that I've seen before include "Common food fish" , "swimmer" , "Fish sold in cans" , "Marine food for your strange aunt" , "Sea creature" .)