The Price of Fish

Fresh cod was £18.99 per kilo at Morrison's supermarket - real cost not realised until after purchase.  Check on the internet showed the best price for the same cod  at Peterhead fish market was £3.50 per kilo.  Who makes the money (£15.49 per  kilo sold)?  Not the fishermen who put in the most effort - no wonder Morrison's can afford the massive extension to our local store. But then I guess it's always been like that.