I have never heard 'another kettle of fish' but hey I've not spoken to every English speaking person in the world either I think it's visual in origin. If you put a lot of fish together into a small space (like a kettle) they are all over the place, on top of eachother and trying to jump out--same idea as "opening a can of worms."
Random English phrases... I also like mixing them: 'he was half a brick short of two planks'...
I love the colors and design and concept
that squirrel on the tree is great