I'm assuming you're talking about freshwater crayfish? If you are, then it depends on what species of crayfish that you have. I do know however, for the Australian Red Claw crayfish, an excerpt from this link:
http/govdocs.aquake.org/cgi/reprint/2003/704/7040090.pdf
"the female red claw, like native crayfish, attach the eggs to the swimmerets under their tail or abdomen. The eggs remain attached through the incubation period. The incubation period may last 4 to 6 weeks depending on water temperature. At 82F the incubation period averages 30 days. Individual eggs are oval and about 1/10 of an inch in diameter. Females carrying eggs are called “berried†females. Berried females are easily recognized because they tightly curl their abdomen under the body for the first 10 to 14 days after spawning. They are also less active during this period."
And I have read somewhere before that you should seperate the male from the female as soon as you see her with eggs. I would recommend you to download that pdf file if your crayfish is a red claw. It has a lot of useful information IMO...
Hope I am of some help
But then again, if you're talking about saltwater lobsters, I have no clue at all.
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tHNKS FOR UYR HELP