The scales on this egg are not just any kind of common scale: they are scales of pure gold, which make them highly valuable. Removing a single scale from a Koin egg, however, will drastically reduce the hatched creature's life expectancy and ability to see.
A Koin egg that is left untouched by greedy predators, which is rare, hatches and develops into a beautiful, shimmering fish whose composition is pure gold. Koins glow with various hues of yellow and orange under both sunlight and moonlight and are known to sparkle even in the dark.
Koins' eyesight, unlike many other species of freshwater fish, is superb and crystal clear. With careful watch, they are known to scavenge the floor of the Ark River for lost jewelry, pearls, diamonds, and other valuables and return them to a safe place. "Koin Hunting" has become a popular pastime among Arkians, although it's a bit of a misnomer, as you aren't actually hunting Koin creatures themselves but instead their hidden stashes in the riverbed.
Arkians will occasionally find a pile of Koin treasures but many of them are stolen away quickly by Dragolds before they're even spotted.