Fish people oddly want? (7)
I believe the answer is:
Here is my best explanation:
'fish' is the definition.
(pollack is a kind of fish)
'people oddly want?' is the subsidiary indication.
'oddly' means one should take alternating letters.
'want?' becomes 'lack' (wanting is a kind of lacking).
The alternate letters of 'people' are 'pol'.
(Other definitions for pollack that I've seen before include "Fish of the cod family" and "Food fish of the cod family".)