How Goldfish Are Classified

Anyone who has ever been to a large pet store, or who has seen a program on the goldfish as a species, knows that there are an amazing range of varieties, involving differences in the eye, fins, and body color, that can be very exciting additions to your aquarium or pond.

But as a species, the goldfish is usually broken down into three categories that relate primarily to their color or appearance of color. Because all goldfish have transparent scales, "color" that you see is more often a result of the influence of light on the lower layers of the dermis, the deepest layer of its skin.

The three groups of goldfish are known as metallic, nacreous, and matt. The metallic name is self-explanatory, and applies to those varieties with gold or silvery appearances. Nacreous goldfish have a pearlescence to their scales, which is also self-explanatory, and means that they have the same sheen as pearls, which are created by layers of nacre shed by mollusks to cover grains of dirt that get inside their shells. Matt goldfish are like matt paint. They are a flat, non-shiny or reflective color.

Goldfish have a substance known as guanine in their dermis. The level at which it exists, can dictate the color of the fish. In metallic goldfish, there is a good supply of guanine in the upper dermis, which allows for more reflection of light through the transparent scales.
Nacreous goldfish have guanine deeper in the dermis, which means less reflection, and a diffused, pearly glow. Matt goldfish have no guanine at all, and their bodies reflect no light because of that, so the "finish" to their outside, is very flat and dull.

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