A note on sex ratio, size at maturity, fecundity and breeding season of the portunid crab, Thranita crenata (Rüppell, 1830) from the Pakistani coast

Abstract

Abstract Specimens of the portunid crab, Thranita crenata (Rüppell, 1830), commonly known as spiny rock crab or crenate swimming crab, were collected from Buleji rocky shore, in Karachi, during March 2015 to February 2016. The size (recorded as carapace width measured between the tips of the 5th spines) at which male and female crabs attain maturity was 42.6 mm and 42.4 mm CW, respectively. The smallest size of an ovigerous female crab was 38 mm CW. Although there were some more male crabs than female crabs in the samples, the male to female ratio was not significantly different from 11 (). Sex ratios in different size groups and different months were also found insignificantly different from a 11 ratio. Ovigerous females were found throughout the year, with a major peak in May and a minor peak in October when, respectively, 30.04% and 25.12% of the female crabs were ovigerous. The minimum and maximum fecundities recorded were 42 800 and 193 433 in females of 35 mm and 77 mm CW, respectively, and the average fecundity was 107 856 ± 50 331 over all berried females.