Notes: Looks best with 3 rows of fish, max 30x30px. Bigger can work too but taller than 90px or wider than 220px overflows/looks janky.
Creatures like crabs/snails look good on a fourth row, because they're in the sand. See examples.
No scrollbar, so more than four lines and it doesn't wrap and will overflow.

Critters made so far:

3 lines of 20x20px images, with a space in-between, no line breaks above

1 line of 20x20px images, with a space in-between, 3 line breaks above

1 line with 80px tall image, no line breaks above

1 line with 220px wide image, one line break above (borrowed from DA)

A whole bunch of 20x20px images, with a space in-between, no line breaks above, with scrollbar for vertical overflow

A bit of experimenting with 20x20px invisible spacers and multiple images of diff sizes