Why Do Goldfish Turn White in the Dark? A Natural Phenomenon Explained

In a quiet tank tucked away in a shadowy room, a goldfish swims gently in circles. Once radiant with bright orange and shimmering gold, its scales now seem pale—almost ghostly white. To an untrained eye, this might look like a health issue or a sign of aging, but there's a much simpler explanation behind this subtle transformation: light—or more specifically, the lack of it.

Goldfish (Carassius auratus), beloved for their vibrant hues, actually owe their beautiful coloring to more than just genetics. While inherited traits do play a role in determining whether a goldfish will be red, orange, white, or even black, environmental factors like lighting significantly influence how these colors are expressed over time.

The Science of Pigmentation

Goldfish, like many animals, have pigment-containing cells in their skin called chromatophores. These cells come in various types, each reflecting or absorbing light in specific ways. The most important ones in this case are melanophores (responsible for black/brown hues), xanthophores (yellow), and erythrophores (red/orange).

These chromatophores don’t just produce pigment—they react to light exposure. When a goldfish lives in a well-lit environment, the cells are stimulated, and the vibrant colors are maintained. In contrast, when the fish is kept in constant darkness, those cells become less active or “dormant.” Over time, the color fades—often leading to a white or pale appearance.

Darkness and Disappearing Color

This isn't a quick process. The change usually occurs gradually, and it’s reversible to some extent. Once reintroduced to a brighter environment, many goldfish begin regaining their colors. However, prolonged exposure to darkness might cause permanent fading in some cases.

Interestingly, this change isn't a sign of illness. Goldfish in dark environments can still remain healthy and active—as long as their other basic needs are met. It’s just their outward appearance that alters.

Some goldfish owners first notice this transformation after placing their tanks in dimly lit areas, covering tanks at night for extended periods, or moving them to rooms without windows. It's a harmless side effect of their biology adapting to new surroundings.

An Evolutionary Leftover?

While domestic goldfish have long been bred for beauty, their ancestors—wild carp—had duller coloring that served a purpose: camouflage. These fish lived in murky rivers and ponds where bright coloring wasn’t an asset. The tendency for color to fade in darkness may be an evolutionary remnant, showing how adaptable goldfish remain even after centuries of selective breeding.

A Reminder About Environment

This phenomenon is a gentle reminder that lighting matters in more ways than one. For aquarium owners, it's not just about showcasing the beauty of their aquatic pets—it also affects the physical traits of the fish themselves.

If you want to preserve the brilliant color of your goldfish, ensure their environment mimics natural light cycles. Providing them with at least 12 hours of light daily can help maintain their iconic hues.

Final Thought

A goldfish’s color isn’t just skin-deep—it’s a living reflection of its surroundings. When darkness takes over, it doesn't hurt the fish, but it does gently erase the fiery orange we’ve come to associate with them. It’s a fascinating insight into how something as simple as light can alter the very identity of a living creature. In a way, it shows us how nature constantly adapts—even in the smallest glass bowl on your desk.

Hungry for More?

Nature is full of subtle magic. From color-changing fish to glow-in-the-dark scorpions and beetles that "bleed" on purpose, the animal kingdom never stops surprising us. Curious to learn more weird and wonderful facts about other creatures? Stay tuned as we dive deeper into animal adaptations that defy logic—but are 100% real.