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Aspects of the reproductive biology of Portunus sanguinolentus from the west coast of Sri Lanka
were studied from February 2014 to January 2015. Berried females were observed throughout the
year, confirming that they were continuous spawners; however, peak spawning was in October. The
gonadosomatic index of females was significantly higher than the males (GLM; p < 0.05). Sex ratio
fluctuated seasonally and a significantly higher male to female ratio was observed in October (χ2
test). Size at first sexual maturity was estimated at 9.75 and 9.40 cm carapace width for males and
females, respectively. Three types of external egg masses, stages I, II and III, were identified based
on the colour of berried eggs. The mean (±SD) diameter of eggs in each stage was 253.8 ± 3.19,
281.8 ± 6.79 and 316.5 ± 9.78 μm, respectively. The estimated fecundity of P. sanguinolentus varied
from 1.12 × 105 to 1.38 × 106. We propose a new method to identify the maturity stage of the male
gonad using external characteristics. Males with mature gonads have blue colour patches on the
ventral side of the chelar propodus and merus but this was not prominent in males with immature
gonads and absent in females.
