 Like other stingrays, the roughtail stingray is aplacental viviparous: the developing embryo is initially sustained by yolk and later by histotroph ("uterine milk", containing proteins, lipids, and mucus) delivered by the mother through finger-like projections of the uterine epithelium called "trophonemata". Only the left ovary and uterus are functional in adult females. Off the eastern United States, reproduction occurs on an annual cycle with mating in winter and early spring. After a gestation period of 9 – 11 months, females give birth to 4 – 6 (typically five) young in fall or early winter. The newborns measure 34 – 37 cm (13 – 15 in) across. Off North Africa, birthing occurs in June and December, indicating either that females bear two litters per year with a four-month gestation period, or that there are two cohorts of females bearing one litter per year with a ten-month gestation period. The newborns are much smaller than those in the northwestern Atlantic at 8 – 13 cm (3.1 – 5.1 in) across, which would be consistent with a shorter gestation period. The size at maturity also differs between the two regions: off the eastern United States males and females mature at 130 – 150 cm (51 – 59 in) and 140 – 160 cm (55 – 63 in) across respectively, while off North Africa males and females mature at 80 cm (31 in) and 66 – 100 cm (26 – 39 in) across respectively.
