Re: Can a crayfish lay eggs that are not fertilized?

Hi Sherri,

Wow, I think it's cool that your 3rd grade students are learning about crayfish! They're really interesting animals, aren't they?

Crayfish, like many crustaceans, are obligate copulators. The following information generally applies to the familiar malacostracan crustaceans such as crabs, lobsters, and crayfish. The sperm of these animals are not flagellated and do not swim, so to insure fertilizaton the male must place them directly onto or into the female's body. Usually the female stores sperm for a while, then as the eggs are laid they pass over the sperm and are fertilized. She carries the fertilized eggs on her pleopods (abdominal appendages, also called swimmerets) and cares for the embryos until they hatch.

According to The Crayfish Corner, mating in North American crayfish occurs in the fall, and gravid females (referred to as "in berry") are seen the following spring and early summer. Thus female crayfish can store sperm for about 6 months. In the case of your crayfish, I don't think it's likely that the eggs she laid are fertile, for a couple of reasons. First of all, even if she's as old as 15 months, in May 2003 (the last time she had been in contact with a male) she would have been only about 6 months old, which is probably too young to be sexually mature. Second, even if she had mated in May 2003, it's likely (but not certain!) that the sperm would be dead by now.

Based on my personal experience with marine crabs kept in captivity, I can tell you with absolute certainty that mature females are quite capable of producing clutches of eggs even if they haven't mated. I have collected juvenile female rock crabs (Cancer antennarius ) and kept them for up to two years. One of them, named Brutus in honor of her truculent personality, produced two clutches in the time that I kept her. She had not been in contact with other crabs since I brought her into the lab, so the eggs were unfertilized, but the absence of male contact didn't prevent Brutus from ovulating.

All things considered, I'd have to say that your crayfish's eggs are unfertilized and won't hatch. Still, it will probably be a good learning experience for your students to observe how she carries the eggs under her abdomen and fans them with her pleopods.

I hope this answers your question! Thanks for sending it to us.

Allison J. Gong
MAD Scientist

References:
Ruppert and Barnes, 1994. Invertebrate Zoology, 6th edition. Saunders College Publishing.
Brusca and Brusca, 2003. Invertebrates, 2nd edition. Sinauer Associates, Inc.