There are several advantages to buying whole fish from your local fishmonger and doing the filleting yourself.
Most fishmongers buy whole fish directly from the fishing boats and then they pay their staff to fillet, skin, bone and pack the fillets ready for sale in their shop. This amounts to a significant labour cost. In most fish factories (and decent sized fresh fish shops) professional fish filleters cut the fillets and then other staff do layer packing, weighing etc. All of this labour increases the cost of the fish fillets you buy, so you really will save if you do your own filleting.
When you buy whole fish you can check the freshness quite easily whereas it takes more experience to tell the difference between fresh fillets and fillets that are past their use-by date! Everyone who works in the seafood industry knows this, and unfortunately some fishmongers do get away with selling fish fillets that have been cut from fish that would never pass inspection if left whole.
Any fishmonger who has a few tubs of 14 day old fish sitting in the chiller with grey gills, sunken eyes and a rank smell knows that they can still sell that fish if they want to. All they need to do is fillet them, cut off the rotten yellow belly flaps, wash the fillets in iced water, pop them on a clean white tray with a sprig of parsley and put them in the shop display.
Now, we are not claiming all fishmongers do such things but we have been around the industry long enough to know that it certainly does happen, and much more than you probably think.
If you fillet your own fish you can make use of the head, wings and frame which typically just get tossed in the bin.
For example: fish wings are very tasty on the BBQ or they can be used to make stock. You can also use the fish frame and head in stock. Some fish, like WA Dhufish even have a large scallop of cheek meat in the head that you can cut out.
Fish heads also make great bait for your crayfish pots!
Take a look at our free fish filleting tutorial videos if you aren't sure how to fillet the fish you buy.