Finned Swordfish
Short answer: a Swordfish in which one row has a cell outside the three columns. If that cell — the fin — sits in one box, then either the Swordfish is real or the fin holds the shape, and both put the shape in that box. Strike it from the covered cells there.
What a finned Swordfish looks like
Clean Swordfish are rare. Finned ones are not — as a fish grows, the chance that every line stays perfectly inside the pattern falls away, so most three-line fish you meet will have a fin on them. That makes this the most useful page in the fish family, and the one worth learning even if you never find a clean Swordfish in your life.
Everything about the pattern is the same as a plain Swordfish; only the payoff shrinks. Instead of clearing all three columns, you clear the part of them that lies in the fin's box — usually one or two cells, occasionally enough to break the puzzle open.
How to use a finned Swordfish
- Look for three rows that nearly agree. List, for each row, the columns that can still hold your chosen shape. You want three rows whose columns pool to four — three real ones plus one intruder.
- Identify the fin. The intruder is the fin: one or two cells in a base row sitting outside the three columns. If they are spread across two boxes there is nothing to be had, so stop there.
- Take the intersection. The elimination is the cells that lie in one of the three columns AND in the fin’s box, and that are not part of the pattern. Nothing outside that intersection is safe.
- Strike and re-scan. Remove the shape from those cells only. Then look again from scratch — a finned fish elimination often turns the position into one where a plain X-Wing or a locked candidate becomes visible.
The same trick at other sizes: finned X-Wing for two lines, finned Jellyfish for four. If the fin turns out to be in the pattern's own box rather than outside it, you had a plain Swordfish all along and can strike the columns entirely.
Finned Swordfish vs Swordfish
A plain Swordfish is cleaner to explain and far more satisfying to find, but if you only look for clean ones you will do a lot of scanning for very little. The finned version reuses the entire search — same shape, same rows, same list of columns — and only changes what you do when the pool comes to four columns instead of three. In practice you are not learning a second technique, you are learning not to give up on the first one.
Find Finned Swordfish in your own grid
Paste a puzzle and this page will look for Finned Swordfish in it — the same pattern shown above, in your grid instead of ours. Nothing is uploaded; it runs in your browser.
Frequently asked questions
Can a finned Swordfish have two fins?
Yes, as long as both are in the same box. The argument only ever needs "if the fish is false, this box holds the shape", and two cells in one box still guarantee that. Two fins in different boxes guarantee nothing.
Why is the elimination so much smaller?
Because you have proved less. A clean Swordfish rules the shape out of all three columns; a finned one only rules out the cells where the two possible worlds overlap. Small eliminations are still eliminations, and this one is often the only move on the board.
Is a sashimi Swordfish different?
Only in name. Sashimi means the pattern also has a gap — one base row does not reach every column — and the reasoning and the elimination are unchanged, so it is not treated separately here.
Should I look for these before or after wings?
After. XY-Wings, skyscrapers and colouring are quicker to scan for and eliminate more when they hit. Reach for a finned fish when the cheaper techniques have all come up empty.