Fish people oddly want? (7)
I believe the answer is:
'fish' is the definition.
(pollack is a kind of fish)
'people oddly want?' is the wordplay.
'oddly' means one should take alternating letters.
'want?' becomes 'lack' (wanting is a kind of lacking).
The alternating letters of 'people' are 'pol'.
(Another definition for pollack that I've seen is " Food fish of the cod family".)