Studies on reproductive biology and ecology of blue swimming crab Portunus pelagicus from Chilika Lagoon, Orissa, India

Portunus pelagicus a commercially important crab species found in Chilika lagoon constitutes about 20% of the total crab production. The carapace width (CW) ranges from 4.5-10.5 cm in both the sexes during the study period. The maximum abundance of male was at 6.6 to 7.5 cm CW whereas the females predominate from 6.6 to 9.5 cm CW. The relationship between carapace length (CL) and CW is linear in both sexes which indicates isometric growth. However, the relationship between CL, ON with total body weight (TW) is exponential. The food habit from gut content analysis shows that the species is highly carnivorous and the main food items include prawn carapace and appendages (27.58%), molluscan remaining (21.55%), fish bone (7.75%), seagrass (1.72%), unidentified materials (4.31%) and the mixed food (37.06%). The feeding index was found highest (80.95%) in February whereas it is lowest (60.9%) in June. The mature females are observed from May to July with a peak in July in the lagoon. The highest gonadosomatic index is found in July with an average CW of 10.5 cm. No berried females are found in the study period, which indicates that it did not spawn inside the lagoon and migrates to the sea during the rainy season.