Don't worry, not every Garfield ends in cold-blooded murder. Some end with a live animal inside a character.
The last two days have featured Garfield interacting with another talking animal. On first glance, today's strip makes more sense than yesterday's joke which relied on a dog being illiterate, but a cat being able to read. Here, Garfield gives the set-up ("There's a great big world out there")... but since it's not his own punchline ("Your stomach IS fat!"), I can't figure out what he was trying to tell the fish in the first place.
Nor do I know why if Jon continues to insist on buying fish, he not only refuses to put them in aquariums of the proper size, with rocks in the bottom, but puts them on the same table where Garfield's meals are eaten.