Gender Differences in Comet Goldfish

Goldfish are the most commonly kept pet fish in the United States. The comet goldfish is often grouped with the common goldfish, but it is in fact a variation of the common goldfish species. Telling these species apart is difficult, and more so trying to determine a fish's gender. Take into account the physical differences and mating behaviors of the comet goldfish to properly discover the fish's gender.

  1. Size Differences

    • Comet goldfish, in general, tend to be smaller than the common goldfish.

      The male comet goldfish tends to be smaller and have a more slender body than the female. Unless you are a professional fish breeder, it is nearly impossible to tell the gender of the fish until it reaches maturity. Maturity occurs when the fish grows to about 3 to 5 inches, and maturity can happen in as little as 10 months, or it can take up to three years for the fish to reach maximum maturity.

    Internal Differences in Male Comet Goldfish

    • The male comet uses its slender build to pursue the female.

      The male comet goldfish will begin to develop small bumps, called tubercles, on its gill plates and head once it reaches maturity. The goldfish's abdomen will become firmer and may develop a ridge, to assist the male with conducting reproductive activities. The vent on the tail end of the fish where excrement is released is more concave in comparison to the female's vent.

    Internal Differences in Female Comet Goldfish

    • The female will be bullied by the male to release her eggs.

      Much like the male, the female will develop tubercles on her body, though they will only appear on her gill plates. The female comet during mating season will also be larger, thicker and have a supple body, as she must have a softer body to safely carry the eggs. Her tail vent actually sticks outward, allowing for easier release of the eggs.

    Male Comet Goldfish Behavior During Mating

    • Chasing is a common action used by egg-laying fish for breeding.

      The male will pursue the female to no end until she releases her eggs for fertilization. The slenderness and aerodynamic body of the male is used to constantly chase the female until she is ready to spawn. Sometimes the male comet becomes too aggressive in his pursuits and begins to physically push the female at any chance he gets, or he may pursue the female to the point of exhaustion.

    Female Comet Goldfish Behavior During Mating

    • Fish will only release eggs where they believe it is safe.

      The female comet will grow thicker from the presence of eggs and will look a bit lopsided because of the egg growth. She must constantly dodge the advances of the male comet until she is ready to release her eggs. Once she feels the eggs are ready, she will release them where the male can easily fertilize them and where they will safely grow.