Hello and thank you for your message,
Unfortunately from what I know there is no way to sex the dusky jawfish. You can read more about this in this article, but below is an excerpt from it:
"Mating, spawning, and the rearing of jawfish fry has been successful in home aquariums. A 4' tank is recommended for the pair in so much as natural territories of jawfish range from 1 - 3'. In spawning season (Spring through Fall), sexual dichromatism is present in some species. The Yellow head jawfish gains black spots on the ventral side of the head, while the Blue spot jawfish's posterior becomes white. Outside of spawning season there is no sexual dichromatism."
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