Re: how do you tell a boy crayfish from a girle crayfish when they are babys?

Hi Vanessa,

When I got your question to answer, I did a lot of thinking about crayfish, then I looked in some books that I have, then I asked a friend who knows a lot about crustaceans (the major group of animals that crayfish belong to) what he thought. He told me that it would be very difficult to determine the sex of a juvenile crayfish without dissecting the animal and looking at its internal structures. I assume you don't want to do that with your crayfish, so you probably won't be able to tell if they are male or female until they grow to adulthood.

Even when sexually mature, male and female crayfish look an awful lot alike, and you can't tell them apart without very close examination. If you want to try sexing your adult crayfish to see if you really have one female and one male, here's what you'd do:

Your crayfish walks on four pairs of legs that are on its thorax -- go take a look at your crayfish and see for yourself. These legs, plus the pair of claws, are called thoracic walking legs. In mature male crayfish, there is a gonopore (a small opening through which gametes are released to the outside of the body) at the base of the 5th pair of walking legs. In a female crayfish, the gonopore is located at the base of the 3rd pair of walking legs. Mind you, these gonopores are very small and difficult to find, so don't be too disappointed if you can't see them.

The following websites have pretty nice photos of the anatomy of male and female crayfish. Click on the numbered dots to pull up information about anatomical structures, including the gonopores. You can actually see them in these photos! To orient you to the animal's position in these pictures, the head is to the right, and the tail is to the left.

I hope this answers your question, and that you enjoy your pet crustaceans. They do make good pets, as long as you keep them fed and their water relatively clean. Good luck!

Allison J. Gong
Mad Scientist