Morphometrics, length-weight relationship and relative condition factor in Charybdis (Archias) omanensis septentrionalis Türkay & Spiridonov, 2006 (Brachyura, Portunidae) from the Arabian Sea

Charybdis (Archias) omanensis septentrionalis Türkay & Spiridonov, 2006, has recently been recorded from the Arabian Sea, while the first record of the species was from the Red Sea. The specimens were collected in a shrimp trawl from a depth of 65-68 metres from the southwest coast of the Arabian Sea, off Kerala, India. The species size ranged between 17 and 37 mm carapace width, from 11 to 22.5 mm carapace length and in total weight between 0.39 and 5.53 g. The interrelationships between various morphometric characters, viz., carapace width and length and chelar propodus length and height in males, as well as carapace width and length and abdominal width and length in females, were estimated for the species and it was found that most relationships are positive and highly significant. In the carapace width/length-weight relationship, the estimated b values for carapace width-weight in males, females and pooled, were 2.674, 2.719 and 2.783, respectively, and for carapace length-weight they were 2.601, 2.588 and 2.681, respectively. The results show a significant deviation from an isometric growth pattern. An analysis of covariance indicated that there is a significant difference between sexes with respect to the carapace width/length-weight relationship. The relative condition factor values estimated in males and females were 0.9794 ± 0.16 and 1.1280 ± 0.26, respectively, also recording a significant variation ( P < 0.01) between sexes