This gets asked a lot. First answer was not helpful so here’s the real answer from John Wiessinger at eNaturalist–
If you look on the underside of the tail, you’ll see small, paired extensions called swimmerets. In females, they’re all about the same but in males, the first pair (those closest to the body) are enlarged and fold up toward the head. The male's specialized swimmerets allow the male to fertilize the female…
Next time you want this sort of answer, use the right terms in the search–
“How to sex ________” or “Sexing ______”
See, science can be fun.
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