system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why is saltwater marine life usually so much more colorful and vibrant?
gpt
If you’re talking about aquarium fish, it isn’t because they’re saltwater. Plenty of saltwater fish are boring. It’s because they’re tropical. Animals throughout the tropics are more colorful  and if you were going through the trouble of having a saltwater tank (which is very difficult to take care of), then you might as well select the most colorful and interesting looking ones. And in the ocean, there are way more to choose from.

People think the reason tropical animals are more colorful is that given the biodiversity and density it’s more important for species to find each other for mating than to avoid predators.