Looking for a fish that is REALLY flashy?
Something that catches your eye as you walk by?
Try a little school of Neon Tetras!

But do they really glow in the dark, or do they just reflect light? And why do they glow anyway? Is it to attract mates, scare predators, or just to show off?
Here, we'll reveal the secrets behind these flashy fish, and help you decide if they're right for your aquarium.

Neon tetras are one of the most popular and colorful freshwater fish in the aquarium hobby. They are native to the Amazon basin, where they inhabit blackwater and clearwater streams with acidic pH and low mineral content. They belong to the same family of fish as piranhas, but they are much more peaceful and harmless.

 

Do Neon Tetra fish actually glow in the dark?

The short answer is no, not technically.

Neon tetra fish do look like they produce light when it's dim, but not 'glow' in the way you might think. They do not produce their own light, like some bioluminescent organisms do. Instead, they have a special ability to reflect and enhance the light that falls on them, making them appear to glow. This process is called fluorescence, and it is different from phosphorescence, which is when an object emits light after being exposed to light.

Here's the science:
Fluorescence is a phenomenon that occurs when certain molecules absorb light of a specific wavelength and then re-emit it at a longer wavelength. For example, a fluorescent object might absorb ultraviolet (UV) light and then re-emit it as visible light. This is why some objects, such as highlighters, your teeth, or a white tshirt, appear brighter under a black light.

Neon tetra fish have fluorescent pigments in their skin and scales that can absorb blue or green light and then re-emit it as red or orange light. This makes their colors more vivid and intense, especially under artificial lighting. However, this also means that they need some source of light to glow in the dark. If you turn off all the lights in your room, including the aquarium light, you will not see them glow. But if you shine a flashlight or a black light on them, you will see them sparkle like little stars.
This is why so many of us love to keep them in dim blackwater tanks. In addition to mimicking their natural habitat, and those tannins being oh so beneficial... that tea stained water also really sets off their trademark 'glow'!

Why do neon tetras appear glow in the first place? What is the evolutionary advantage of having this ability?

There are several possible explanations for this, but none of them are conclusive. One hypothesis is that fluorescence helps neon tetras communicate with each other and form schools. By reflecting and enhancing each other's colors, they can signal their presence and location to their mates and avoid predators.

Another hypothesis is that fluorescence helps neon tetras camouflage themselves among the plants and algae that also fluoresce under natural sunlight. By matching their flash to their surroundings, they can blend in and avoid detection.

A third hypothesis is that fluorescence helps neon tetras attract prey or mates by making themselves more visible and noticeable. 

This seems counterintuitive, right?

By displaying their colors more brightly, they can lure in smaller fish or impress potential partners.

Want to see a REAL light show? 

When the lights are all off at night, grab a flashlight and shine it on your tank. 

Hard to believe these guys are completely natural.... They almost look fake!

 

If you’re interested in learning more about neon tetras and the common myths surrounding them, check out our blog post titled 'Myth Busting: Neon Tetra Edition'!.

 

Neon tetra fish are amazing creatures that can add color and life to your aquarium. They do not glow in the dark by themselves, but they can reflect light that makes them look like they are glowing under certain conditions. They have fluorescent colors that help them survive and reproduce in their natural habitat.

Isn't natural selection amazing?

Thank you for reading!