How to Tell the Difference Between Male & Female Seahorses

Seahorses are famous for their ability to gender bend: the males incubate the embryos in their bodies, essentially becoming pregnant. However, the physical differences between the genders, especially outside the breeding season, are subtle. If you just see one seahorse, you might not be able to tell whether it is a male or female at first glance. With a pair or group, distinguishing between the sexes is more straightforward.

Things You'll Need

  • Plastic ruler
  • Guidebook
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Instructions

    • 1

      Compare the sizes of the seahorses. Normally the female is significantly larger than the male.

    • 2

      Examine the colors of the animals. Female seahorses usually have brighter colors than the males.

    • 3

      Observe the seahorses' behavior. Males have one stereotypical male quality--they are more aggressive. In a large group, males may fight for a female. Seahorses fight by entangling their tails and head butting each other.

    • 4

      Examine the front of the seahorse. Males have a pouch extending from the bottom of the belly down that is especially obvious in "pregnant" males.

    • 5

      Measure the seahorse by placing the ruler close to it. Compare your measurements to the averages for males and females of that species in a guidebook. Assuming the seahorse is fully grown, the height provides an indication of whether it is a male or female. Seahorse measurements are taken from the tip of the tail to the top of the head. You might have to estimate part of the tail length.