Fishing Tips

Cleaning Flatfish

Posted 4/15/2014

Everyone’s favorite fresh-caught seafood is flounder. Here’s how to clean them like a pro.

Seems no matter where you fish in the coastal waters of the world, there is a flatfish of one species or another available to anglers. In the United States, if we start in New England and work our way around the country to the West Coast, you can encounter Atlantic halibut, yellowtail flounder, black back or winter flounder, four-spot flounder, summer flounder (commonly called fluke), southern flounder, Gulf flounder, California halibut and Pacific halibut. They range from small fish that might average a pound or two, like the winter flounder, to enormous flatties that can reach 9 feet in length and weights to over 500 pounds, like the Pacific halibut. 

They vary in availability and range from estuaries to deep ocean waters. Some are scavengers like the winter flounder, while others are voracious predators like the summer and southern flounders and all the halibuts. Some species are at low levels of abundance, primarily the Atlantic halibut, which has become a very rare catch in U.S. waters, while others are exceedingly abundant, like the fluke. The most common trait is that they are asymmetrical in body shape or for lack of a better term—flat!

Interestingly, they aren’t born that way. All flatfish start life looking rather unassuming as baby fish go until Mother Nature does her sleight of hand. Their eggs hatch into larvae that resemble typically symmetrical fish. The larvae quickly develop into a rounded form with protective spines on the head, over the gills and in the pelvic and pectoral fins. They are born with a swim bladder for buoyancy to make it easier to roam near the surface and feed on plankton, but as they grow they turn into “Frankenfish.” One eye migrates across the top of the head onto the other side of the body, the swim bladder and spines literally disappear, the body coloration on the sightless side turns white, while the other side assumes a darker coloration that provides camouflage for lying on the bottom. That’s important because the bottom is where these critters spend the majority of their time, either scavenging for a meal or lying in wait for a hapless fish or crustacean to get too close – and wham!

Flatfish like this 5-pound fluke are fun to catch and with a little simple knife work, provide some of the best table fare you can pull from the sea.

For anglers in the U.S. flounder are a favorite target species, not because they are a hard-fighting game fish, but because they are fun to catch and great to eat! You can’t get around the fact that most recreational fishermen enjoy catching fish to eat, and flounders are pretty much at the top of the list. Most of the flatfish that anglers catch are of the smaller varieties, so we would like to pass along a technique that many consider the best way to fillet them. 

For the best tasting flounder, try bleeding and icing immediately after landing. Lift the gill plate, cut the gill rakers with a scissor or knife, then put the fish in a live well or bucket of water to bleed out. When that’s done, put the fish on ice in a cooler to firm up the meat for easier cleaning and to maintain the quality. 

Step 1 

To get started, all you need is a fish like this four-pound summer flounder and a long, straight, sharp, flexible fillet knife. The cleaning board with clamp is optional, but if you’re cleaning a lot of fish, it’s a time saver. 


Step 2 

Start white side down, and make your first cut across the tail just forward of the fin.


Step 3 

Insert the point of the knife into the first cut and slide it as far forward toward the head as possible running it alongside the spine, represented by the red line. You’ll be able to feel it. 

Step 4 

With the knife angled just slightly down so the blade is running along the rib bones, slice carefully outward to detach the filet. On larger flounder you might have to reinsert the knife to complete the cut all the way to the head. 

Step 5 

Repeat the process on the belly side of the fish, but make the slice carefully so the knife doesn’t cut into the stomach cavity outlined in red. 

Step 6 

This is what it looks like after the two cuts. The fillet is only attached directly behind the head. 

Step 7 

Detach the fillet with a single cut as shown, being careful not to penetrate the stomach cavity and set it aside.

Step 8 

Turn the fish over and repeat the process on the bottom (white side) fillet.

Step 9 

Carefully remove the feathers, the tiny muscles that power the fins around the flounder’s perimeter. 

Step 10 

Lay the fillets on the cutting board skin side down, and use your finger tips to hold the very end of the tail section. Make a downward cut to the skin, turn the blade almost horizontal to the table, and carefully push the blade toward the far end using a slicing motion to separate the meat from the skin.

Step 11 

When done, you have a single fillet from the top and bottom of the fish that can be divided into four smaller fillets by slicing down the middle where it is thinnest, (the section that was over the backbone). For smaller fish this is not necessary; for larger fish the split fillets are more single-serving friendly.Y