Observations on the reproductive biology of the Bull ray, Pteromylaeus bovinus (E. GEOFFROY SAINT-HILAIRE, 1817) (Chondrichthyes: Myliobatidae) from the coast of Senegal (Eastern tropical Atlantic)

Abstract

         The bull ray, Pteromylaeus bovinus (E. GEOFFROY SAINT-HILAIRE, 1817) is commonly caught off the coast of Senegal. Adult males and females were over 820 mm and 900 mm disk-width (DWd) respectively, with the largest male and the largest female recorded being 1150 mm and 1480 mm respectively. They weighed 29.8 kg and 47.9 kg respectively. The females were significantly heavier than the males. The DWd of eight fully developed fetuses ranged from 250 to 270 mm DWd (mean: 258.70 ± 8.33), their total length (TL) from 530 to 560 mm (mean: 541.27 ±11.20) and their weight from 310 to 345 g (mean: 326.25 ±13.29). The smallest free-living specimen was a female; its DWd was 355 mm, its TL 585 mm and it weighed 460 g. Diameter of ripe oocytes ranged from 22 to 26 mm (mean: 23.6 ± 0.14); they weighed from 4.1 to 6.3 g (mean: 5.25 ± 0.61). Gestation lasted between 5 and 6 months. It appeared a block of oocytes at the beginning of gestation and there was an inability to ovulate soon after parturition. Vitellogenesis recommenced when the embryos were practically at the end of their development. The reproductive cycle lasted one year at least. A calculated chemical balance of development based on mean dry weights of the fully developed fetuses and the ripe oocytes is 31.12. This high value shows that P. bovinus is a pure matrotrophic species. Counts of ripe oocytes, eggs, embryos and fully developed fetuses showed that ovarian fecundity is higher than uterine fecundity. The former ranged from 6 to 8, the latter from 3 to 4. There were no relationship between size and both categories of fecundity. In the sample, both adult males and females are more abundant than the juvenile ones. Among the adults, males are significantly more numerous than females.