South American resistance eat fish (7)
I believe the answer is:
sardine
'fish' is the definition.
(sardine is a kind of fish)
'south american resistance eat' is the wordplay.
'south' becomes 's' ('S' can be a synonym of 'south').
'american' becomes 'a' (common abbreviation - e.g. in organisation names).
'resistance' becomes 'r' (abbreviation).
'eat' becomes 'dine' (dining is a kind of eating).
's'+'a'+'r'+'dine'='SARDINE'
(Other definitions for sardine that I've seen before include "Small fish, usually canned" , "FRENCH FISH" , "Rinsed a (anag) - fish" , "A diner's small fish" , "Stonefish OR? Stone" .)