gsf wrote:this one requires 3 swordfish

Congratulations! - first puzzle I have seen in this category!

Analysis

First: Swordfish (with Swordfish dual, both with cp 2+2+2 / ep 2+2+1) (one choice)

Second: Swordfish (with Jellyfish dual) (cp 2+2+2 / ep 1+1+1) (one choice)

Third: Swordfish (with Jellyfish dual) (cp 2+2+2 / ep 1+0+0) (one choice)

[cp: cell pattern / ep: elimination pattern]

No branch of the solution path (when non-splus techniques are treated as iterative group).

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For classificaton, maybe it's relevant to distinguish between the various fish types (subtypes):

1. JF/5-F (Jellyfish with a 5-fish dual)

2. JF/JF (Jellyfish with a Jellyfish dual)

3. SF/6-F (Swordfish with a 6-fish dual)

4. SF/5-F (Swordfish with a 5-fish dual)

5. SF/JF (Swordfish with a Jellyfish dual)

6. SF/SF (Swordfish with a Swordfish dual)

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