Reproductive cycle of the common guitarfish, Rhinobatos rhinobatos (Linnaeus, 1758), in Alexandria waters, Mediterranean Sea

Abstract

The common guitarfish, Rhinobatos rhinobatos, is an ovoviviparous fish having a gestation period of about nine months and a mean reproductive rate of 8 to 14 progeny per pregnancy. Data on gonadosomatic index, maximum ovum diameter, size frequency of ova, and ovarian and uterine contents for 438 specimens (236 females and 202 males), analysed on a monthly basis, indicated a distinct seasonal reproductive cycle for R. rhinobatos. Females reached a maximum size of 181 cm and 20 kg, whereas the maximum size of males was 172 cm and 16 kg. Lengths at which 50% of specimens were mature were 87 and 70 cm for females and males, respectively. Ovarian egg size and male gonadosomatic index both peaked in July and August, indicating that mating occurred in summer. Uterine eggs were present from late February through July, but no embryonic development was evident. Females with full-term embryos were observed in late August, and parturition was followed immediately by ovulation. Ovarian fecundity ranged from 8 to 27 (mean 18) eggs per fish, whereas uterine fecundity ranged from 8 to 14 (mean 12) eggs or embryos per fish.