According to 'Yesterday's Wirral - Port Sunlight' (Ian Boumphrey and Gavin Hunter) Mac Fisheries and a general store were in this large building on the corner of Bolton Road and Bridge Street, until it was destroyed by a land mine in the blitz of 1941.
It must have moved to the Gymnasium, next to the closed swimming pool, at that time. I can only remember it being a 'wet fish' shop, as above, but the general store may have moved, as well.
The other two paragraphs below are from the 'Port Sunlight Village' guide of 1988.