Turbot Fish

A Turbot Fish is a single-digit solving technique that uses a loop of odd length. The minimum length is 5, forming a fish-shaped pattern that gave the technique its name. Longer loops are possible, but they are better known as Fishy Cycles.

Here is an example of a Turbot Fish:

.-------.-------.-------.
| . | . | . | . | . . . |
| . X . | . X . | . . . |
| . | . | . | . | . . . |
:-------+-------+-------:
| . | . | . | . | . . . |
| . X . | . | * | . . . |
| . | . | . X . | . . . |
:-------+-------+-------:
| . | . | . | . | . . . |
| . | . | . | . | . . . |
| . | . | . | . | . . . |
'-------'-------'-------'

The candidates in columns 2 and 5 are strongly linked. The pattern causes either r5c2 or r6c5 to be true. Since r5c6 can see both these candidates, it can be eliminated.

This pattern is also known as Skyscraper.

The following pattern is also a Turbot Fish:

.-------.-------.-------.
| . . . | . - . | . . . |
| . * . | . X . | . . . |
| . . . | . - . | . . . |
:-------+-------+-------:
| . . . | . - . | . . . |
| - X - | - - X | - - - |
| . . . | . X . | . . . |
:-------+-------+-------:
| . . . | . - . | . . . |
| . . . | . - . | . . . |
| . . . | . - . | . . . |
'-------'-------'-------'

The candidates in row 5 and column 5 are strongly linked. The pattern causes either r5c2 or r2c5 to be true. Since r2c2 can see both these candidates, it can be eliminated.

This pattern is also known as 2-String Kite.