Dear Blue Lobster:
I have two fresh water blue lobsters and I hope to breed them. I can't tell if there male or female. Can you help me determine their gender? How can you tell if they are male or female? Also, does it matter if one is about 1/8 of an inch smaller than the other?
Dear Gentle Sir:
Unfortunately, checking a cray's gender is not as easy as lifting its legs and peeking. It involves being able to classify your cray by species, molting phase, and health. It's no surprise that even most professionals can only guess at gender and typically use breeding pools instead of breeding pairs.
Knowing your cray's species is the first step: Do you have a Red Swamp Crayfish (Procambarus clarkii) or a Red Bayou Crayfish (Procambarus kentii)? Without first knowing the species, gender identification becomes difficult, if not impossible, as we shall see below.
A crayfish's phase is the next important thing to know. A phase is simply a morphological structure the cray adopts for mating. Their phase changes at molts and comes during breeding season. Crays exposed to videos of mating pairs have also molted into a breeding phase.
The structural differences are unique among genera and species. For instance, a male Red Jaconda Cray (Cancerita rojoña) during non-breeding Phase I resembles a female Clouded Cray (Cancerita nublado), a closely related species. As you can see, this gets complicated.
Overall health is one last factor. Obviously, a cray whose appendages have been chewed off completely will be difficult to sex, as will one which is too small to study closely. Also, not all cray species exhibit sexual dimorphism, so size isn't a good identifier unless you first discern the species.
One method of sexing crays scientists have had some success with has been taking cray whose gender is known, grinding it into a paste, and releasing the paste into a holding tank with other crays of the same species. The crays that respond first will be members of the opposite gender to the ground cray, as they respond to the pheremones in the offal.
Good luck identifying your cray's species, gender, and phase. If you're lucky you'll have a well-known species you can identify quickly and without much mess.