Upon reaching sexual maturity the female is typically inseminated by a male each time she molts. The spermatophores are stored in the closed thelycum of the female, which is a modification to the posterior thoracic sternal plates and is a flesh covered chamber which can maintain viable sperm throughout the inter-molt period. The stored spermatophore is lost each time the female molts, so the female must be inseminated each molt cycle if fertilised eggs are to be produced. Insemination only occurs within a few hours of molt when the female’s shell and thelycum are still soft. The mechanism by which a male and female find each other in this short time in turbid estuarine or coastal water is not known. Since P. monodon occurs at low population densities in North Queensland and throughout most of its geographical range in Australia, it must be a highly efficient mechanism. In the North Atlantic lobster (Homarus americanus), the male produces a chemical signal (pheromone), which can attract pre-molt females from great distances. In the lobster mating takes place within 30 minutes after the female completes her molt (Cowan and Atema 1990).

Mating in P. monodon has only been observed in captive broodstock. Generally, mating takes place at night immediately after the female molts. The female is followed by one or more males which swim parallel to her. The male bends its body so there is ventral-ventral contact and turns perpendicular to the female. A spermatophore pair is released from the male’s terminal ampullae and inserted through the slit between the lateral plates of the female thelycum into the chambers underneath; there are two separated chambers, each for one of the two spermatophores, on either side of the thelycum ridge (Motoh 1981). Courtship and mating varies from 0.5 to 3 hours and requires parallel swimming over considerable distances. For mating to occur successfully in captivity large rectangular holding tanks may be required for uninterrupted swimming during mating (Primavera 1988). Alternatively, successful matings can be obtained in circular 4 meter diameter tanks having 1 meter water depth.