Sefa Ayhan Demirhan

Age and growth of the common guitarfish, Rhinobatos rhinobatos , in Iskenderun Bay (north-eastern Mediterranean, Turkey)

Age and growth of the common guitarfish (Rhinobatos rhinobatos) were estimated from the north-eastern Mediterranean coast of Turkey. A total of 115 common guitarfish (66 females and 49 males) were sampled. Age determinations were carried out using vertebral sections. Alcian blue dying techniques were used to enhance the visibility of the band on vertebrae. The techniques have been used for the first time on elasmobranchs vertebrae successfully in this study. A total of 97 vertebrae of 115 were visible on the vertebral band in this study. Male and female common guitarfish ranged in age from i to 15 and i to 24 y respectively. Total length ranged from 42 to 147 cm for females and 39 to 124 cm for males. The relationships between total length (TL) and total weight (TW) were presented as TW = 0.0054*TL 3.672 (R 2 = 0.98) for females, TW = 0.0012 *TL 3.1947 (R 2 = 0.98) for males and TW= 0.0012*TL 3.1915 (R 2 = 0.98) for both sexes. The parameters for von Bertalanffy growth curves were estimated as L inf = 137.70 + 9.38 cm, K = 0.159 + 0.047, to - 2.180 + 0.90 for pooled data.

Biological observations on the common guitarfish Rhinobatos rhinobatos from İskenderun Bay (Turkey, Eastern Mediterranean)

Histological examination of the gonads showed that spermatogenesis occurs in every male R. rhinobatos collected in autumn and winter months of the year. Th e testis was composed of lobes having numerous spermatocysts in a dorsoventral zonated arrangement. Present results suggest that since R. rhinobatos have a cystic mode of spermatogenesis it can be used as a model for biomedical and toxicological studies. Eight stages of maturation for females and seven stages of maturation for males were identifi ed. Moreover, vitellogenic oocytes were consistently found in every female collected during the summer months. In vitellogenic oocytes, yolk is present as pleomorphic droplets and very often; small yolk droplets have a crystalline confi guration. Th ese data suggest that both sexes are reproductively active at diff erent times of the year. Both, the right ovary/testis and the left ovary/testis were functional. Ripe oocytes in the ovaries were usually symmetrically distributed. Th e population consisted of aplacental viviparous individuals with lecithotrophic embryo development. Although, sex ratios of R. rhinobatos were not signifi cantly diff erent from the expected 1:1 ratio (p>0.05), slightly female biased sex ration were recorded.