Comparability in dietary elements, sex ratio and fecundity of portunidae crabs Callinectes amnicola (De Rocheburne) and Portunus validus (Herklots) off Lagos coast

Abstract

Crabs of the Portunidae family are distinguished by their paddle-shaped fifth pair of legs adapted for swimming and are good source of protein for the coastal communities. A total of 1002 samples (472 specimens of Callinectes amnicola and 530 specimens of Portunus validus) were collected from trawl catches off Lagos Coast and studied for their dietary elements, sex ratio and fecundity. A comparative analysis was done on both Portunidae crabs during the period April to September 2016. From the specimens of C. amnicola examined for food and feeding habits, 110 (23.3%) had empty stomachs while 49 (9.2%) of the P. validus examined had empty stomachs. The diet of crabs studied constituted mainly fishes, crustaceans, molluscs, annelids, plants materials and unidentifiable matter. In both crabs, fishes constituted the dominant food source and these were present in 44.1% and 41.1% of the stomachs analysed for C. amnicola and P. validus respectively. A Chi square (χ²) test for the sex ratio of C. amnicola (1:0.98) was not significant at P<0.05, however, P. validus with sex ratio 1:1.45 showed significant difference. C. amnicola was observed to be a low fecund crab with fecundity estimates varying from 278,000 to 2,150,500 eggs for mature crabs measuring 8.0-14.9 cm carapace length and 58.0 – 125.0 g total body weight, while P. validus was highly fecund with fecundity estimates ranging from 606,400 to 5,300,520 eggs inmatured female crabs measuring 11.0 cm to 18.0 cm carapace length and 270.0 g to 616.0 g total body weight. Conclusively, this study revealed that C. amnicola and P. validus showed similarity in dietary items but variations in sex ratio and fecundity.

Keywords: Fecundity, sex ratio, nutrients, Portunidae, Lagos Coast