Common Goldfish

Brewing Alcohol Without Oxygen

Without oxygen, most vertebrates die within minutes. Goldfish (Carassius auratus) are an exception. Fish of the genus Carassius, the crucian carp and the goldfish, survive prolonged periods without oxygen by producing ethanol as their metabolic end-product. Ethanol is the alcohol in drinks.

Yeast chemistry in a fish The trick rests on a pyruvate decarboxylase, an enzyme (a protein that speeds up a chemical reaction) analogous to the one in brewer’s yeast and the first described in vertebrates. It works alongside a specialized alcohol dehydrogenase.

Four Colors and a Motion Sensor

Goldfish are tetrachromats, meaning they can see four colors: red, green, blue and ultraviolet. Along each side runs the lateral line, a row of sensory organs that helps them detect motion in the water around them. Herons, northern river otters and American bullfrogs can prey on goldfish. To defend against predators, goldfish form large groups called schools, and they warn each other with chemical signals that predators are nearby.

A Bottom-Feeding Pond Bulldozer

Goldfish originated in eastern Asia, including China, Hong Kong, Korea and Taiwan, and the range of the species expanded to most of the world. They tend to live in bodies of water with slow or no movement: ponds, lakes, rivers and marshes.

Size depends on where the fish lives. Goldfish generally reach 15 to 20 centimeters and weigh 100 to 300 grams, though the USGS lists a maximum of 59 centimeters and 3.0 kilograms. In captivity, goldfish grow to about 2.5 to 15 centimeters, and wild goldfish often grow bigger than domesticated ones because their environment offers more resources and space to swim. Lifespan is typically 6 to 7 years, and it has been reported as long as 30 years.

They are generalist omnivores that eat insects, eggs, plants and crustaceans. Goldfish feed at the water bottom, where they stir up sediment and increase turbidity, which is how cloudy the water is.

They are tough: adult goldfish can survive water temperatures between 0 and 41 °C. Young goldfish hatch with dark, pigmented scales, which fade 2 to 3 months later. Females normally spawn 2000 to 4000 eggs at a time, and adult goldfish consume their own offspring.