Jellyfish

Extreme Used by Smart Hint

A height's candidate cells across four rows (or columns) line up in the same four columns (or rows) — eliminate it everywhere else in those columns or rows.

Cells that establish the pattern
Where the conclusion lands
Height ruled out

How it works

The same fish one size larger again: four rows, four columns. Follow height 1 down the top four rows.
Row 1 allows it in columns 1-2, row 2 in columns 2-3, row 3 in columns 3-4, row 4 in columns 1 and 4. Four rows, and between them only columns 1, 2, 3 and 4.
Four rows each need their 1, and only those four columns can provide one — so all four columns are used up before the bottom row gets a look in.
Strike 1 from the bottom row's first four cells. Its 1 must be in the last column.
This is the top of the fish ladder: a five-row fish on a 5x5 board would just be restating that every row needs a 1.