Well done. I'm always impressed when people come up with a cool puzzle mechanic. I'm even more impressed when they come up with good puzzles too.
I gave up on puzzle 5 or 6. Don't get me wrong, I would have kept playing, but having to restart a puzzle because of a mis-click or a mistake is really rough. And I've got other games to rate. I think it is good practice to allow a one-step undo when you die. Now if I get myself into an unwinnable position, that's on me, I'll use a restart button. But I don't think the game would suffer from infinite undo either.
At the very start I didn't realize that they can move sideways. I think I was thinking of that cars game where they only go forward and backward. Having one of two levels where all you do is move one creature sideways is never a bad idea.
On web, at least, the clicking and dragging was really rough. I got unexpected movements when I just clicked and let go a few times. One led to a death when I was already in the clear. The 1x1 shrimp does not like leaving, I've gotta really slam him, lol.
I wanted the level to end when I only had one color left, but mostly because moving then was tedious. If the controls were cleaner I probably wouldn't have had that thought.
I'm giving a bit of criticism, but this is coming from a place of love. If you clean up the graphics a bit, fix the mouse controls, add one or two more mechanics that you sprinkle in later on, then bam! Put it on steam for $1.99, have occasional 50% off sales. I can't guarantee that it will sell, but it will deserve to be there.
Also, I need something better than color to keep track of who eats who. I don't have any good ideas, but we should brainstorm some up.