My GF asked why saltwater fish are so much more colorful. Not having an answer wouldn't be masculine so I came up with one on the fly.

Well babe, through evolution the smaller shallow water fish became more brighter and colorful so that predators would be able to easier spot them. then I thought about it and that can't be right. Evolution gives you tools of survival not demise. So does anyone have a better answer just in case one of her college professors ever ask and I make her look like a fool. I answered it like it was a stone cold fact so I think I sold her on it.

I would say that saltwater fish aren't inherently more colorful than freshwater fish, if anything the opposite is true. If you remove the coral reef species, you have many others like cod, pollock or herring that have little of the rainbow in them.

Here's a paper that may lend some insight:

http://www.ncbi.nlm....df/11079407.pdf

There's more out there, but I'm pretty sure this is the study that kicked it all off (about the right time) - and it helps this is available to everyone.

Todd

Your concern seems to mainly be about reef fish, most northeastern saltwater fish I have seen are dull colored.

On the topic of fish coloration, I wonder why tropical fish in pet stores are colorful all year long while northern fish need special temperature conditions to get colorful.

Tropical reef fishes live in a stable environment, while temperate species go through cold and warm seasons.

Quiz her fresh or salt with these. Neither fresh nor especially salt are shown at the peak of color, but I went with what I have in my tanks right now [and pics handy].
as to temporate marine species showing color, you need to do some snorkling on a sunny day to see some color. It's not like coral reefs, but plenty color none the less.
Get back in the estuaries and find some sheepshead and mummichugs in breeding colors and you will think they were tropical. Both species hold their iridescence in captivity BTW.




I bet the rest of the folks here can come up with some killer shots of freshwater fish far more colorful than the ones I put up.
Let's see 'em!

Edited by mikez, 27 February 2010 - 11:58 AM.

I got this one sampling with Jan this fall. It's a freshwater fish .... saltwater fish..... freshwater fish ..... saltwater fish .... anadromous!



Plus I am glad I kick netted a salmon, I am glad Jan took a pic before I released it. It's my current bragging fish.

Good point FirstChaos. Her point of reference is the LFS. MikeZ is that your Red Bellied Dace? The more I see pics of those the more I want some. They are beautiful fish.

yeah the red bellies are incredible. mine still have the same color from when we collected them in sept in VA

The first thing you need to do is remember that our own perceptions of fish color are not really important. One must consider how the fish is seen by predators, prey and potential mates in its natural environment.

Saltwater reef fish often seem colorful to us when viewed through 6" of water under metal halide lighting. But, clear water filters out red light very quickly leaving a spectrum of green/ blue light. So, "bright red" fish actually look camouflaged in their natural environment. Since they use their "bright" colors as camo they keep them all year. Serious diver photographers spend as much money on powerful lighting as do reef keepers!
For an example I present the humble squirrel fish:
With extra lighting


With out:


Temperate freshwater fish (that I am familiar with) tend to live in shallower more turbid water. To avoid predators they have to closely match their surroundings. Unless... they are trying to attract a mate. In that case the males need to be seen. Henceforth seasonal spawning colors (at least as far as our primate eyes can detect).

Also remember that different fish have different levels of color vision. One good rule of thumb is spawning colors = color vision. There is no point in changing into a red, blue and green billboard if the ladies can't see color anyway. Fish that are best adapted to foraging in low/ no light conditions generally sacrifice color vision to get better low light detection (rods vs cones). These same fish also tend to lack dramatic spawning colors. (i.e. brook trout vs lake trout)