Morphometrics, length-weight relationships and relative condition factor in Portunus sanguinolentus (Herbst, 1783) from the southeastern Arabian Sea

Abstract Portunus sanguinolentus is widely distributed all along the Indian coast and constitutes the most dominant marine crab landed in the country. In Kerala also, the species’ share is maximal in the marine landings and recorded an average of 1200 tonnes during 2007-2020. The bulk of the catch is contributed by trawlers and the species is mainly fished from the 20-30 m depth zone. It grows to a maximum size of 20 cm in carapace width (CW) and the estimated life span is approximately three years. Knowledge on the body weight-length/width relationships and relative condition factor in populations is important for estimating the population size of a stock and its exploitation. Hence, morphometric relationships between various characters, viz., carapace width (CW) and length (CL) and chelar propodus length (CPL) and height (CPH) in males, as well as CW and CL and abdominal width (AW) and length (AL) in females, were estimated using a total of 2476 male and 2965 female crabs. The CW/CL-weight relationship was studied in both sexes on a total of 5595 crabs using the allometric growth equation. The allometric relationships between the characters of this set suggest that most relationships are positive and highly significant ( ). The b values for CW-weight in males (55-171 mm/CW), females (54-170 mm/CW), and pooled were 2.9657, 2.8028, and 2.8914, respectively. The results show an isometric growth pattern for males and considerable deviation from isometric growth in females, also when all sizes are pooled. An analysis of covariance indicates that there is a significant difference between sexes ( ) with respect to the carapace width-weight relationship. The relative condition factor ( ) values estimated in males and females (based on CW) were 0.942 ± 0.145 and 1.371 ± 0.255, respectively, and the estimated values based on CL were 0.985 ± 0.204 and 1.022 ± 0.233, respectively.