Used as a technique for a single digit (_x_), the turbot fish is a short [X-cycle](https://sudokubliss.com/guides/x-cycle) built from four cells that begin and end with strong links (two conjugate pairs). It allows you to eliminate candidate _x_ from cells that see both ends of the pattern.

Many Sudoku players discover turbot fish while learning the logic of advanced techniques like [X-wing](https://sudokubliss.com/guides/x-wing-technique) and other fishy cycles. Whether you're a developing solver or already deep into puzzle solving, this turbot fish technique is a helpful addition to your Sudoku solving toolkit.

## How to Find a Turbot Fish in Sudoku

![Turbot fish example](https://sudokubliss.com/content-uploads/turbot-fish-example.webp) 

Use these steps to easily find a turbot fish for a single digit (_x_) in your Sudoku puzzle:

1. **Find the first strong link (conjugate pair) for candidate (_x_) to begin the turbot fish.** A conjugate pair occurs when candidate _x_ appears only two times in a unit, and because one candidate or the other must be true (the answer), the pair creates a strong link. So find _x_ appearing exactly twice in one unit (row/column/box) to find the first strong link. For example, candidate 8 appears exactly twice in the first block in A2 and B1, creating the first strong link.
2. **Find the second strong link for candidate (_x_) that will end the turbot fish.** In a different unit (row/column/box), x appears exactly twice to create a second strong link. For example, candidate 8 appears exactly twice in column D (D1 and D7), creating the second strong link that will end the pattern.
3. **Find a shared link for (_x_) between the two strong links.** The two strong links must connect to another link that contains candidate _x_. For example, candidate 8 appears three times in row 1, so B1 and D1 create a weak link for the candidate. The turbot fish is a compact alternating inference (AIC) chain, but this [advanced technique](https://sudokubliss.com/guides/sudoku-advanced-strategies) still works when the middle link is strong. However, like in this example, the shared link is often weak.
4. **Target candidates for elimination in cells that see both ends of the fish.** For example, because A7 sees both ends, also called tips, of the turbot fish pattern (A2 and D7), the 8 in A7 can be deleted. Although candidate 8 in B7 shares a row with D7, it can't see the other endpoint (A2), which means it cannot be eliminated.
![Example grids proving turbot fish logic](https://sudokubliss.com/content-uploads/turbot-fish-logic.webp) 

**Why this works:** If 8 is true (or the answer) in A2, then it can't be the answer in A7, and if 8 is true in D7, then the 8 cannot be the answer in A7\. Even with the weak link, you can prove this to be true by following the logic.

* **Starting with 8 true in A2:** If 8 is true in A2, it automatically eliminates 8 from A7 because it's in the same column. So you don't need to follow the chain through to make the pattern work.
* **Starting with 8 false in A2:** If 8 is false in A2, then 8 has to be true in B1\. If true in B1, then 8 must be false in both D1 and E1\. That means 8 must be true in D7, and 8 has to be eliminated from A7.

Either way, an 8 cannot be the answer in that cell because one tip or the other must contain candidate _x_ (in this example, 8).

## Standard Turbot Fish Examples

A standard turbot fish is simply a four-cell X-chain (not a fish pattern) that starts and ends with a strong link. One strong link must be diagonal within a block and the second strong link must be found within the same row or column.

Other [solving strategies](https://sudokubliss.com/guides/sudoku-tips-and-strategies) may be considered turbot fish, but they go by their own names and have their own solving strategies. For example, [skyscraper](https://sudokubliss.com/guides/sudoku-skyscraper) and empty rectangle are types of turbot fish, but they don't follow the standard, simple pattern. A [two-string kite](https://sudokubliss.com/guides/2-string-kite) is also considered a type of turbot fish, but it uses a weak leak on the diagonal in a block.

### Turbot Fish in a Row

![Turbot fish in a row example](https://sudokubliss.com/content-uploads/turbot-fish-in-a-row-example.webp) 

Find a standard turbot fish with a second conjugate pair in a row by following these steps:

1. **Look for the first strong link between two diagonal cells in a block.** F1 and D3 both have a strong link with candidate 5 because candidate 5 appears just twice in that block.
2. **Find the second strong link for the same candidate in a row.** Candidate 5 appears only twice in row 6, creating a strong link between D6 and E6.
3. **Find the shared link with the same candidate to connect the two strong links.** D3 and D6 create a weak link for candidate 5 because it appears three times in that column, and it connects both strong links into a chain.
4. **Eliminate candidate _x_ (5) from cells that see both endpoints.** F5 shares a column with F1 and a block with D6, so the 5 in F5 can be eliminated. Note that the 5 in F8 only sees F1\. Because it doesn't see both ends of the chain, candidate 5 cannot be eliminated from that cell.

### Turbot Fish in a Column

![Turbot fish in a column example](https://sudokubliss.com/content-uploads/turbot-fish-in-a-column-example.webp) 

Find a standard turbot fish with a second conjugate pair in a column by following these steps:

1. **Look for the first strong link between two diagonal cells in a block.** Candidate 4 creates a strong link between A1 and C2 because 4 appears just twice in that block.
2. **Find the second strong link for the same candidate in a column.** Candidate 4 appears only twice in column E, creating a strong link between E2 and E8.
3. **Find the shared link with the same candidate to connect the two strong links.** C2 and E2 create a weak link for candidate 4 because it appears four times in that row, and that link connects both strong links into a chain.
4. **Eliminate candidate _x_ (4) from cells that see both endpoints.** A8 shares a column with the first cell in the first strong link (A1), and it shares a row with the last cell of the second strong link (E8). So the 4 in A8 can be eliminated. Note that the 4 in A5 only sees A1\. Because it doesn't share a unit with the other endpoint (E8), candidate 4 cannot be eliminated from that cell.

Sometimes you just need one elimination to unlock an [expert](https://sudokubliss.com/expert) or evil-level puzzle. So the next time you're [playing Sudoku online](https://sudokubliss.com), try finding a turbot fish when you get stumped and see if it enhances your solving strategy.