How to Determine if an Oscar Fish Is Male or Female

Oscar fish (astronotus ocellatus) are a type of fish that belong to the cichlid family. They are freshwater fish native to the Amazon and are commonly used in household freshwater tanks. Oscar fish are considered to be sexually monomorphic, as sex cannot be differentiated by simply looking at the fish. Often people attempt to identify the sex by looking at the color, size of the fin and overall size of the fish, but these methods are inaccurate. The best method of identification is through observation of the spawning process.

Things You'll Need

  • 2 Oscar fish
  • Active freshwater tank that is at least 48 by 15 by 18 inches kept at 26-30 degrees C
  • 8 by 10 inch piece of slate
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Instructions

  1. Process

    • 1

      Make sure your Oscar fish are at least 18 moths old. Oscar fish will start breeding at this time. The time frame may vary depending on the water warmth, food and size of the tank. If the appropriate conditions are kept, spawning will occur about once a month.

    • 2

      Raise the temperature of the freshwater tank to 28 degrees C. This will encourage the spawning process.

    • 3

      Place the piece of slate into the fish tank. The Oscar fish will use choose the flat surface of the slate to lay eggs on.

    • 4

      Observe the fish. They should become more aggressive toward other fish that come near their nesting area.

    • 5

      Notice a couple of days before the Oscar fish spawn--they will stop eating and the female Oscar fish will begin to show a creamy white egg tube. This is the first identification of sex.

    • 6

      Observe the female lay eggs. She will lay from 12 to 20 at a time until around 1,000 to 2,000 eggs are laid.

    • 7

      Watch as the male Oscar fish will be swimming closely behind the female. The male will have a protrusion from below the belly closer that looks like a thorn. This is the male genitalia of the Oscar fish and he will be fertilizing the eggs.