Why is it that tropical saltwater fish are so much more colorful than their freshwater counterparts?

Because, believe it or not, in the sunny, clear, shallow waters around coral reefs, the best way to hide is to be brightly colored in that brightly colored environment. However, in most freshwater habitats you need to be brown, green or silver to disappear or look like something that is not edible. Hence, colorful fish are found in the tropical oceans, and “boring” fish are found in ponds, lakes, rivers and streams.

I suppose that makes sense. But you can certainly see the bright, colorful fish swimming around in the shallow waters in Hawaii. Although I’m sure they are probably better hidden from underwater predators with that colorful reef in the background.

The bright color in fish usually warns predators that they are poisonous. Thus, they will less likely be eaten.

When we see reef fish in aquariums or in photographs, we’re struck by their bright colors, but this is largely because we’re viewing them in full-spectrum light. In their natural environment, beyond a few meters of depth, most of the longer wavelengths of light have been filtered out. This radically alters how the pigments are perceived. Red would appear as black since there is virtually no red light, and blue would blend with the predominantly blue ambient light. Most underwater photos are taken with artificial light which supplies wavelengths not normally present where these creatures live.

@Harp- Perhaps, but most of these fish live in coral reefs and not a few meters underwater, don’t you think?

@AstroChuck Ah… But these coral reefs are a few metres underwater, see?

@AstroChuck The part of the reef with the greatest number of fish species is not the shallow reef flat, but the fore reef, which extends down well below the point at which red is filtered out, which happens at about 10 meters. 10 meters is still considered the upper reaches of the fore reef.

Fish species certainly venture between zones, and many will seek feeding opportunities in shallow areas where their colors make them more conspicuous, but these are also not the areas where most of the larger reef predators lurk. Down where the larger predators are, colors are less of a liability.

Ah, gotcha. Thanks.
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