Gonadal cycle of the blue crab Portunus segnis (Forskål, 1775) (Decapoda, Portunoidea) in the Mediterranean Sea off Alexandria, Egypt

Abstract

Abstract Adults of Portunus segnis were captured from Ras el Tin beach on the Mediterranean Sea at Alexandria, Egypt, from January to December 2017. Male crabs are present in higher density in the sea during fall and winter, while female crabs are more common during spring and summer. Sex ratios were calculated as follows: number of males or females/total number of crabs. The calculated sex ratios were subjected to a Chi-square test according to the equation: , where O represents the observed frequency and E the expected frequency. One-way analysis of variance shows differences in the carapace size (length and width) and the weight of males and females during the four seasons. The hepatosomatic index of male crabs ranges from 9.1-9.25 in winter months, 8.7-7.9 in fall, being lower, 3.12-2.25, in spring and 5.96-4.13 in summer. The hepatosomatic index of female crabs is 8.9-3.9 in spring, 9.2-7.9 in summer, shifts lower to 5.1-3.2 in fall and to 4.2-1.5 in winter. The gonadosomatic index of female crabs is 0.12-8.2 in spring, 0.20-13.9 in summer and decreases to 0.66-7.8 in fall and 0.18-4.7 in winter. Ovaries and testes were isolated, fixed, and prepared for histological examination. The testicular lobes are surrounded by simple epithelium with haemolymph filling the interspaces. Seminiferous ducts are inserted in the testicular lobes. Spermatogenesis and spermiogenesis are described. The vas deferens is usually filled with spermatophores. Spermatophore formation begins in the testis near the vas deferens. Near the base of the penes there is glandular tissue. This study proposes the classification of the ovarian maturation into five stages: Stage I, Immature ovary with primary and secondary oogonia; Stage II, early maturing ovary with germ cells in different maturation phases; Stage III, mature ovary with vitellogenic oocytes and germ cells; Stage IV, maturing ovary with oocytes I, II and fully mature oocytes; and Stage V, ovary in regeneration. The wall of the spermatheca consists of a stratified squamous epithelium.