To breed most machrobrachium species shrimp you just need to make them happy, with good water quality and no fish to eat any offspring. Also the males can be quite agreesive and territorial, so give them plenty of caves and the like for them to establish nice little territories. In time they will breed. It is important however that their aquarium is quite mature, and that filtration is not too harsh, as the young have an abbreviated larval stage of about 4 days (freshwater) before metamorphosing into shrimplets. As such they require plenty of tiny food stuffs in the water column in order to feed, hence the need for a mature set up which tends to have these as standard.
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