Earning it's stripes!

As lovers of natural, botanical-style, blackwater aquariums, it's almost impossible for us not to love the little fishes which inhabit tropical streams, flooded forests, and  ponds. The habitats are as alluring and intriguing as the many fishes which reside in them.

And of course, that includes the characins- "Tetras", as we have come to call them collectively.

It always amazes me how they all have such vibrant color delineation and contrast, and I got to thinking about just why it is that these little fishes have such intense coloration and, in many cases, contrasting stripes.

In particular, the Neon Tetra, (Paracheirodon inessi) has such a dramatic coloration and pattern that you just had to figure it was for some reason other than just the fact that it looks awesome! (Yeah, Nature really couldn't give two f - - -s about aesthetics, as we know...) Turns, out, I have not been the only one wondering about this stuff.

Scholars have been researching it for years!


A couple of Japanese scientists (Takehide Ikeda and Shiro Kohshima ) were curious about this same thing, and they had a hypothesis about the stripes that was published after they conducted some field studies on fishes of blackwater biotopes (!) in the Peruvian Amazon, along with some aquarium observations as well, back in 2009.

They found that the lateral stripe in the Neon is actually kind of inconspicuous in the blackwater environment...unless viewed from an angle of about 30 degrees..Similar to an angle of attack that a predator might take when pursuing the Neon! From this angle, the stripe is actually "projected" in a near "mirror image" to just beneath the surface of the water.

Totally confusing to a would-be "Neon-muncher!":

"...Although they appeared bright in colorless water, their stripes appeared darker in blackwater. In addition, the visible are of their stripes was small and their brightness decreased, unless they were observed with a limited viewing angle (approximately 30 degrees above the horizon). The results show that from the viewpoint of approaching submerged predators, a bright mirror image of the stripes is projected onto the underside of the water's surface, providing a dramatic visual target while the real fish remains less conspicuous..."

This became known as the "Mirror-Image Decoy Hypothesis" (sounds incredibly sexy intellectual, huh?), and is a brilliant explanation (pun sort of intended) for the unique coloration of the Neon (and possibly the Cardinal Tetral, Glowlight Tetra, and several other Tetras as well, though to a different extent! Although it could be construed that the Neon (and by extension, the Cardinal) have evolved this "decoy coloration" further than many other species, which have a darker-colored lateral stripe and a lighter dorsal stripe, the opposite of the Neon!

"Fish Stealth."

Interestingly, Neons can alter their color intensity somewhat as well; for example, at night, when the colors are "duller- which also helps them blend in a bit more in various water and lighting conditions. Essentially, they change color in response to the lighting and environmental conditions in which they reside as an anti-predatory measure. However, the "Mirror Image Decoy" appears to be a specific adaptation to the blackwater environments from which these fishes predominantly hail from.

Ad one could make that stretch, when enjoying other small Tetras from blackwater habitats- that the coloration corresponds to the characteristics of the habitat directly. In other words, fishes which hail from areas of lighter substrates would likely be light on top, to better blend in with their habitat from above, and vice versa with dark stripes on top.

That would explain some interesting color patterns in many of these small fishes, right?

So we as hobbyists enjoy the chromatic brilliance and color combination of the Neon Tetra, while the fish "enjoys" the protection afforded by this little trick of optics!

And it all started in blackwater.

Kind of a "win-win" adaptation, right?

And that is one theory about how the Neon "earned its stripes!"

Stay curious. Stay educated. Stay inspired. Stay observant...

And Stay Wet.


Scott Fellman

Tannin Aquatics


Volume 86, Issue 3 pp 427-441)


Scott Fellman
Scott Fellman


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