Sashimi Swordfish Sudoku Technique

Updated 11 August 2026

A Sashimi Swordfish is the three-line sashimi pattern: one of the three base lines is missing a candidate at one of the cover lines, but the fish still proves the same finned-style eliminations once the fin’s box is found.

When a Sashimi Swordfish applies

A Finned Swordfish keeps all three base lines close to a full Swordfish shape, with one stray candidate acting as a fin. A Sashimi Swordfish is thinner: one of the base lines has a candidate that would normally sit inside the three cover lines, but instead sits outside them, so that base line contributes only one cover-line cell rather than two or three. The line has been “cut”, in the same sense as the Sashimi X-Wing, and the displaced candidate becomes the fin.

The proof is unchanged from any other finned fish. Every cell that sits inside the three cover lines, outside the three base lines, and shares a unit with the fin, cannot hold the digit — because either the fin holds it, or the base lines settle back into a shape that covers the cell some other way. The sashimi cut only changes how thin the base lines are allowed to be, not the elimination rule itself.

As with the X-Wing’s sashimi variant, this pattern is stricter to confirm than a regular Finned Swordfish, since one base line is down to a single relevant candidate, but it still reaches real eliminations that a plain three-by-three Swordfish would miss.

Worked example

Column 1 has one candidate for 1 in the cover rows: r7c1. Column 7 has two: r4c7 and r6c7. Column 5 also has two candidates for 1 overall, but only one of them, r4c5, falls inside rows 4, 6 and 7 — the other, r9c5, sits in row 9, outside the chosen cover rows. That leftover candidate is the fin, and column 5 supplying only one cover-row cell is the sashimi cut.

r9c5 sits in the bottom-middle box, the same box that holds r7c4, r7c5 and r7c6. r7c6 was carrying 1 and 9 before the deduction. Column 5 is already one of the fish’s own base columns, so it is excluded from the elimination search regardless; r7c6 sits in column 6, inside the box, and inside cover row 7. Whichever cell in the base lines actually holds 1, r7c6 cannot, because it shares the fin’s box and column 5 cannot itself be the source of that elimination. The solver removes the 1 and leaves 9 behind.

How to spot a Sashimi Swordfish

1. Look for a thin base lineFind three lines where a digit’s candidates mostly line up across three cover lines, but one base line has only one candidate inside them.
2. Find that base line’s leftover candidateConfirm the thin base line has exactly one more candidate for the digit, sitting outside the three cover lines. That is the fin.
3. Check which cells share the fin’s boxLook at the cells inside the cover lines, outside the three base lines, and keep only the ones that also share a box with the fin.
4. Eliminate the digit thereRemove the digit from that narrower set of cells, remembering that cells inside a base line itself are never eliminated.

Common mistakes

• Requiring every base line to reach two or three of the cover lines. A sashimi cut means one base line only reaches one.
• Eliminating the digit from a cell that sits inside one of the base lines. Base-line cells are exactly where the digit may still legally go.
• Missing that the fin has to fall in a single box shared with the target cells. If the fin’s remaining candidates spread across more than one box, the pattern does not qualify.
• Confusing which line is base and which is cover. The sashimi cut always applies to a base line losing a cover-line candidate, not the other way around.