Filleting a round fish
Take a whole sea bass, trout or mackerel down to two clean fillets, with the bones left for stock and very little flesh left on the frame.
Why it works
A round fish has a thick, rounded body with an eye on each side and one fillet on each flank. The backbone runs down the middle, with a row of ribs curving around the belly cavity and a line of fine pin bones running out sideways into the thickest part of each fillet. Filleting means separating the muscle from that frame in as few long strokes as possible.
Fish muscle is made of short blocks of flesh held together by thin sheets of connective tissue. That tissue is weak, which is why fish flakes when cooked and why it tears if you saw at it. A flexible blade that stays flat against the bones and moves in long, smooth strokes lets the flesh peel away along those natural seams. Short hacking cuts break the blocks apart and leave ragged edges and wasted flesh.
Doing it yourself has real advantages. Whole fish are easier to judge for freshness than fillets, they usually cost less per kilo of usable flesh, and you keep the head and frame for stock. You also control the thickness of the trim and how well the bones are removed, which matters when you plan to sear skin-side down or serve the fish raw.
The first fish you fillet will be untidy. After four or five the movement becomes automatic. Start with mackerel or trout, which are small, soft-boned and cheap, before moving on to sea bass, cod or a side of salmon.
What you need
- Flexible filleting knife: A blade of 15 to 20 cm that bends against the bones; it must be very sharp, because a dull one tears the flesh.
- Fish scaler: Lifts scales quickly; the back of a cook's knife does the same job a little more slowly.
- Fish tweezers: Flat, wide-tipped tweezers grip pin bones without crushing the flesh around them.
- Kitchen scissors: Strong scissors clip off fins and open the belly faster and more safely than a knife.
- Large chopping board: Long enough to lay the whole fish flat, set on a damp cloth so it cannot slide.
- Kitchen paper: Dry the skin and your hands so nothing slips; a wet fish is a dangerous fish.
Step by step
Choose a fresh fish
Look for clear, bright, slightly bulging eyes and gills that are red or deep pink and moist. The flesh should spring back when pressed and the skin should be shiny with scales firmly attached. It should smell clean and of the sea. Dull, sunken eyes, brown gills or a sour smell all mean the fish is past its best.
Tip: Ask the fishmonger to gut it for you if you are new to this; filleting is the skill worth practising first.
Scale the fish
Hold the fish by the tail and scrape from tail to head against the lie of the scales with a scaler or the back of a knife. Work inside a large clear plastic bag, or in a sink full of cold water, so the scales stay contained. Run your fingers over both sides and the belly afterwards to find any you missed, then rinse and pat dry.
Tip: Skip scaling if you plan to skin the fillets. Mackerel and trout have scales so fine they barely need it.
Trim the fins and gut if needed
Snip off the dorsal, belly and side fins with scissors, cutting towards the tail. If the fish is not gutted, insert the scissor tip into the vent and cut up the belly to the head. Pull out the innards, then scrape away the dark bloodline along the spine with a spoon or your thumbnail. Rinse the cavity under cold water and dry the fish inside and out.
Cut behind the head
Lay the fish on its side with the back facing you and the head pointing towards your knife hand. Make an angled cut just behind the gills and the side fin, slicing down to the backbone but not through it. This marks where the fillet starts and gives you a clean edge to work from.
Tip: Angle the blade towards the head so you capture the thick meat behind the gill plate.
Run along the backbone
Turn the knife so it points towards the tail and rest it in the cut at the top of the spine. Draw it along the back from head to tail in long strokes, keeping the blade almost flat and pressed lightly against the bones. Lift the opened flesh gently with your other hand as you go so you can see the bones. Each stroke should go a little deeper until you reach the backbone.
Tip: Let the knife do the work. If you need force, the blade is either blunt or cutting into bone.
Free the fillet over the ribs
Once you are past the backbone, follow the curve of the rib cage down towards the belly, keeping the blade angled against the ribs. Towards the tail there are no ribs, so slide the knife straight through and out the end. Finish by cutting the belly skin free and lift the whole fillet away in one piece.
Tip: Some cooks cut through the thin rib bones and remove them from the fillet afterwards. It is quicker but leaves more trimming to do.
Turn over and repeat
Flip the fish so the head again points towards your knife hand and the back faces you. Repeat the cut behind the head, the stroke along the backbone and the release over the ribs. The second side is harder because the frame is less stable, so go slowly and keep the fish flat with your free hand.
Remove the pin bones
Lay the fillet skin-side down and run a fingertip from head end to tail along the centre line to find the row of pin bones. Grip each one with tweezers and pull towards the head end, at the angle the bone lies, so it slides out without tearing the flesh. Small fish such as mackerel are easier to deal with by cutting a thin V-shaped strip out along the bone line.
Tip: Draping the fillet over an upturned bowl makes the bones stand up and easier to grip.
Trim the belly
Cut away the thin, fatty strip along the belly edge and any remaining rib bones or membrane. Square off the fillet if you want neat portions. Keep the trimmings for fishcakes, soup or stock.
Skin the fillet
Put the fillet skin-side down with the tail end towards you and cut through the flesh about 1 cm from the tail, down to the skin. Grip that tab of skin with a little salt or a piece of kitchen paper. Hold the knife still at a shallow angle against the skin and pull the skin towards you while wiggling it gently from side to side. The fillet comes away clean while the knife barely moves.
Tip: Pull the skin and keep the knife still. Pushing the knife forward is how fillets get cut in half.
Common round fish at a glance
| Fish | Bones and difficulty | Best cooking |
|---|
| Mackerel | Small, soft bones; easy. Pin bones are best cut out in a strip. | Grill, pan-fry skin-side down, cure or smoke |
| Trout | Fine bones that lift cleanly; easy. Scales are tiny. | Pan-fry, bake, hot smoke |
| Sea bass | Sharp dorsal spines; medium. Scale well if you keep the skin. | Crisp-skin sear, roast, raw as crudo |
| Sea bream | Spiny fins and tough scales; medium. | Sear, grill, bake whole or as fillets |
| Cod and haddock | Large, obvious pin bones; flesh flakes easily, so handle gently. | Roast, poach, batter and fry |
| Salmon | Large fish; medium to hard because of size. Long pin bone row. | Sear, roast, cure, raw if suitable for it |
| Perch and pike-perch | Very sharp spines on fins and gill covers; medium. | Pan-fry in butter, poach |
Troubleshooting
The flesh looks torn and ragged.
The knife is blunt or you are sawing back and forth. Sharpen the blade, then use long single strokes from head to tail. Keep the fish cold, because warm flesh is softer and tears more easily.
Too much flesh is left on the frame.
The blade is angled up into the fillet rather than flat against the bones. Lower the angle until you can feel the knife tick over each bone as it moves. Scrape what remains off the frame with a spoon and use it for fishcakes or tartare.
I cannot find the pin bones.
Run a fingertip slowly along the centre of the fillet from head end to tail, pressing lightly; they catch against the skin of your finger. Bending the fillet over a bowl pushes them up. In some fish, such as trout, they are tiny and soft enough to leave.
The pin bones snap or tear the flesh when I pull them.
You are pulling straight up or towards the tail. Grip close to the flesh and pull towards the head end at the angle the bone lies. Chilling the fillet for 15 minutes firms it and helps the bones come out cleanly.
I cut through the rib bones and they are stuck in the fillet.
Slide the knife flat under the row of ribs from the thick side, keeping it pressed up against the bones, and lift them out as one sheet. Trim off the thin belly flap with them if it is easier.
The knife went through the skin when I was skinning.
The blade angle was too steep, or the knife was pushed forward. Keep it nearly flat, hold it still and move the skin instead. If it tears, regrip the skin further along and carry on.
Knives, spines and temperature
A sharp filleting knife and a slippery fish need your full attention. Raw fish spoils fast, so keep it as cold as you can until it goes into the pan.
- Keep your guiding hand flat on top of the fish and away from the line of the blade, and always cut away from your body.
- Dry the fish, the board and your hands before you start, and put a damp cloth under the board so it cannot move.
- Sea bass, bream, perch, gurnard and weever have sharp fin spines that can puncture skin; cut fins off with scissors before you handle the fish much. Weever spines are venomous: wear gloves, and if you are stung, put the wound in water as hot as you can bear and get medical advice.
- Keep the fish in the fridge at 0 to 4 °C until you start, work quickly, and return the fillets to the fridge on a covered plate as soon as you finish.
- Only serve fish raw if it is very fresh and sold as suitable for raw eating, or has been frozen first as your fishmonger advises.
