People regularly want fish (7)
I believe the answer is:
Here is my best explanation:
'fish' is the definition.
(pollack is a kind of fish)
'people regularly want' is the wordplay.
'regularly' indicates alternate letters (regularly take one letter, leave next etc.).
'want' becomes 'lack' ('lack' can be a synonym of 'want').
The alternate letters of 'people' are 'pol'.
(Other definitions for pollack that I've seen before include "Food fish of the cod family" and "Fish of the cod family".)