In a basic fish, N base rows confine a digit's candidates to N cover columns, and every candidate in the base rows is inside those cover columns. Finned fish relax that perfect shape by allowing one or more extra candidates, called fins, outside the cover columns.

The important trade-off is that the eliminations become narrower. A basic fish can eliminate from the whole cover set outside the base rows. A finned fish can eliminate only where the basic-fish elimination area overlaps with the fin's block influence.

A fin is an extra candidate in a base house that lies outside the cover houses. In the common row-based form, that means an extra candidate in one of the base rows but outside the cover columns.

For the usual finned fish deduction, the fins must be confined to one block. If there are multiple fins, they must all occupy the same block section so that a true fin would eliminate the digit from the same local block area.

Finned fish use a two-case argument:

Case 1: All fins are false. The remaining candidates form a basic fish, so the digit can be eliminated from the cover columns outside the base rows.

Case 2: At least one fin is true. Because the fins are confined to one block, the digit is eliminated from the rest of that block.

A candidate can be removed only if both cases remove it. In a row-based fish, the target must be in a cover column, inside the fin's block, and outside the base rows. This overlap is the elimination zone.

Finned X-Wing: Level 7 (Very Hard)

Finned Swordfish: Level 8 (Expert)

Finned Jellyfish: Level 8 (Expert)

Finned Squirmbag: Level 9 (Master)

A sashimi fish is a finned fish where the underlying fish would collapse if the fin were removed. In other words, one of the base houses contributes too weakly to form the full unfinned fish without the fin. In an X-Wing, this often looks like one base row having only the fin plus one candidate in a cover column rather than the clean two-corner rectangle.

The elimination logic is the same as a finned fish: either the fin is false and the remaining fish logic applies, or the fin is true and its block removes the candidate locally. The difference is visual. A sashimi fish looks incomplete, so you must recognize the near-fish rather than expecting a perfect fish with one simple extra candidate.

Sashimi X-Wing: Level 7 (Very Hard)

Sashimi Swordfish: Level 9 (Master)

Sashimi Jellyfish: Level 9 (Master)

1. Scan for near-complete fish.

2. Identify any fins: extra candidates in the base houses outside the cover houses.

3. Verify that all fins are confined to one block section.

4. Check where that block overlaps the cover houses.

5. Eliminate only candidates that are removed whether the fins are false or true.

6. Consider the sashimi case when the unfinned fish would be incomplete after removing the fin.

Tip: Start by looking for basic fish and notice when they fail by a small, block-confined set of candidates.

Finned X-Wing: Level 7, Occasional

Sashimi X-Wing: Level 7, Rare

Finned Swordfish: Level 8, Rare

Finned Jellyfish: Level 8, Very rare

Finned Squirmbag: Level 9, Extremely rare

Sashimi Swordfish: Level 9, Extremely rare

Sashimi Jellyfish: Level 9, Extremely rare

Finned and sashimi fish extend classic fish to handle imperfect alignments. The fin restricts eliminations to candidates that lie both in the fish's cover houses and in the fin's block influence. Sashimi fish are finned fish whose underlying fish would be incomplete without the fin, making them harder to recognize visually. These seven techniques bridge the gap between basic fish geometry and abstract chain-based techniques.