"Chicken of the sea" (4)
I believe the answer is:
tuna
'chicken of the sea' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for tuna that I've seen before include "Large salt water fish" , "Type of fish" , "A fish; sounds like piano juster" , "Fish, often tinned" , "Tinned food fish" .)