Seafood that's line caught (3)
I believe the answer is:
roe
'seafood' is the definition.
(roe is a kind of seafood)
'line caught' is the wordplay.
'line' becomes 'row' (row is a kind of line).
'caught' shows a homophone (sound like) (to catch something can mean to hear it).
'row' is a homophone of 'ROE'.
'that's' is the link.
(Other definitions for roe that I've seen before include "Fish eggs; small deer" , "Mass of fish's eggs" , "shy animal" , "Lobster's ripe ovary" , "Swift runner" .)