Mashed tater and fish (5)
I believe the answer is:
tetra
'fish' is the definition.
(tetra is a kind of fish)
'mashed tater' is the wordplay.
'mashed' indicates an anagram.
'tater' with letters rearranged gives 'TETRA'.
'and' is the link.
(Other definitions for tetra that I've seen before include "starter for four" , "Accosting and detaining (someone)" , "Small tropical fish" , "With four parts" , "Small brightly-coloured fish of aquariums" .)