The characters are not anthropomorphicThat's just how they look to each other.
The human world in "Pool Party Panic" was the real world.Milo preferring the fish world over his own life, so he ended up committing suicide by drowning in Chelsea's pool.
Fish Hooks - humans are extinctNotice - there are NO human characters ( Pool Party Panic doesn't count) besides Bud. However, Bud acts almost like programmed and sometimes acts like an animal (see "Peopleing"). Humans are probably extinct and Bud became animalistic due to being last human left The pets, however, had scientific experiments. And notice - animals are very, very, cheap and affordable. Nobody is buying them. Due to these facts, humans are probably extinct or on the brink of extinction in the Fish Hooks world. And the horrible human-like creature that hatches from a penny in Peopleing is actually a mutant, but not a human. It's egg just looks like a penny.
Snake has a crush on MouseThere is a lot of these moments in Fish Hooks.