Ultimately, chowder is fish dish (7)
I believe the answer is:
rissole
'dish' is the definition.
(rissole is a kind of dish)
'ultimately chowder is fish' is the wordplay.
'ultimately' indicates one should take the final letters.
'fish' becomes 'sole' (sole is a kind of fish).
The last letter of 'chowder' is 'r'.
'r'+'is'+'sole'='RISSOLE'
(Other definitions for rissole that I've seen before include "Fried and breadcrumbed dish" , "Losers I find in the chopped meat dish" , "Fried ball of minced food" , "Croquette" , "Compressed meat and spices in breadcrumbs, fried" .)