---
title: "Finned Swordfish: Sudoku Technique #32 | Sudoku Flow"
description: "Finned Swordfish: A fin is one extra cell on a base line that stops a Swordfish from being complete, so the candidate is removed only from cells in the fin's…"
url: https://sudokuflow.com/lessons/finnedSwordfish/
language: en
---

[Sudoku technique lessons](https://sudokuflow.com/lessons/) / Finned Swordfish

Lesson 32

# Finned Swordfish

## The rule

A fin is one extra cell on a base line that stops a Swordfish from being complete, so the candidate is removed only from cells in the fin's box, outside the base lines, that lie on one of the Swordfish's three crossing lines.

## Step by step

1. 9 almost forms a Swordfish in three base rows. If one extra cell were not there, every 9 candidate in those rows would sit in one of only three columns. That one extra cell is the fin.
2. Either 9 is in the fin, or the Swordfish is complete. Either way we can remove the candidate 9 from the cells of the fin's box that lie in one of the three columns and outside the three base rows.

[Read the full lesson, with more examples →](https://sudoku.rubigogames.com/techniques/finned-swordfish.html)

In our app, when this technique is the next step, the hint names it and shows you why, step by step. No ads, free to download.

[App Store iPhone, iPad, Mac](https://apps.apple.com/app/apple-store/id6502922368?pt=125379530&ct=sudokuflow_cta&mt=8) [Google Play Android](https://play.google.com/store/apps/details?id=com.rubigogames.sudoku&referrer=utm_source%3Dsudokuflow%26utm_medium%3Dcta%26utm_campaign%3Dlesson)

## Try it on more boards

Each board is a real puzzle from our app, at a moment where Finned Swordfish applies. Find the step yourself, or tap Hint and the app's own hint walks you through it.

Finned Swordfish practice board:

```text
.  .  6  | .  3* .  | .  .  .
1  3  .  | 5  .  2* | .  6  .
.  .  8  | 6* 9  .  | .  .  3
---------+----------+---------
4* 5  1* | 7  2  8* | 6* 3* 9
.  8* .  | .  6* .  | .  5  .
6  .  .  | .  1  5* | 7  8  .
---------+----------+---------
3* 6* 4  | 2* 7* .  | 8* .  5
9  1* 5* | .  .  3  | 2  7* 6*
8* 7  2* | .  5  6  | 3  .  .
```
Digits marked * were filled in by a player; the others were printed with the puzzle.

![Sudoku app icon](https://sudokuflow.com/assets/app-icon.png)

## Want more boards like this?

We also make a Sudoku app for iPhone, iPad, Mac and Android. There are no ads in it at all, it works offline, and when you ask for a hint it shows you the technique instead of just filling in a number.

[App Store iPhone, iPad, Mac](https://apps.apple.com/app/apple-store/id6502922368?pt=125379530&ct=sudokuflow_web&mt=8) [Google Play Android](https://play.google.com/store/apps/details?id=com.rubigogames.sudoku&referrer=utm_source%3Dsudokuflow%26utm_medium%3Dweb%26utm_campaign%3Dsite)

Sudoku Flow is made by Rubigo Games, the developer of the Sudoku app recommended on this site.