Observations on the biology of the common torpedo (Torpedo torpedo, Linnaeus, 1758) and marbled electric ray (Torpedo marmorata, Risso, 1810) from Egyptian Mediterranean waters

Abstract

The reproductive biology and diets of Torpedo torpedo and T. marmorata from Egyptian Mediterranean waters are described. Males and females reached a maximum size of 39.1 and 40.8 cm total length (TL), respectively, in T. torpedo and 38.6 and 61.2 cm TL, respectively, in T. marmorata. The size at maturity of males of T. torpedo and T. marmorata is 18 and 25.5 cm TL, respectively, and of females, is 22 and 35.5 cm TL, respectively. Both species exhibit aplacental viviparity. T. torpedo has a restricted breeding season, and individual females appear to breed annually, whereas T. marmorata females appear to have a more extended reproductive cycle (probably breeding every two years). In both species, males are capable of mating every year. In T. torpedo, mating occurs between December and February, ovulation in March-April, and parturition in late August and September after five to six months of gestation. Individuals of T. marmorata mate between November and January, ovulate between December and February, and give birth the following December after 10-12 months of gestation. Mean embryos sizes are 7.3 cm TL (range 4.6-8.2 cm TL) for T. torpedo and 8.5 cm TL (range 5.8-10.1 cm TL) for T. marmorata. Observations in Egyptian Mediterranean waters show a strong correlation between ovarian and uterine fecundity and the length of the mother in both species. Fish are an important component of the diet of the two species, as, to a lesser extent, are crustaceans for T. torpedo and cephalopods for T. marmorata. Juveniles eat a wide variety of food items, whereas adults feed only on fish.