How to Stop Goldfish Spawning

Raising goldfish can be a rewarding experience, but an aquarium can easily become overcrowded when the fish are allowed to spawn and procreate at will. This can leave you with a difficult decision: Add a second tank that you will have to take care of, or somehow get rid of the baby goldfish. The easiest way to avoid this dilemma is to take steps to prevent the goldfish from reproducing.

Things You'll Need

  • Tank thermometer
  • Magnifying glass
  • Fish bowl
  • Fish net
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Instructions

    • 1

      Check the tank's thermometer. The normal temperature for goldfish is 65 to 68 degrees. Water temperature of 70 degrees or warmer induces spawning. Lower the tank temperature immediately.

    • 2

      Change the water less frequently. Goldfish spawn more readily when the water is fresh, so if you normally change 20 percent of the tank's water every few days, change it less less often.

    • 3

      Use the magnifying glass to check the sex of your goldfish to avoid male and female pairs in the same tank. Determining the sex of goldfish is more difficult when the fish are small, but spawning usually starts when they are ages 2 to 3. Mature males will develop tubercles or whitish bumps on their head or gill covers.

    • 4
      A separate fish bowl can provide protection for the female during spawning.

      Watch your goldfish. When spawning starts, the male will chase the female around the tank and ram into her many times. He does this to expel her eggs so that he can fertilize them. If you observe this aggressive behavior, use a net to transfer the female to a fish bowl by herself for about a week. The separation will break the spawning cycle and help keep her safe.

    • 5

      Look for eggs in your tank. Remove any eggs immediately before they hatch into fry. If there might already be eggs in the tank, add a few bottom-feeder fish to eat them.