Relative growth and morphological sexual maturity of the shrimp Macrobrachium acanthurus (Wiegmann, 1836) (Decapoda; Palaemonidae) in a river in Southern Bahia, Northeastern Brazil
allometry; caridea; sexual dimorphism; propodium; second pleura
Macrobrachium acanthurus (Wiegmann, 1836) is an important fishing resource for Brazilian carcinofauna. It has a wide geographic distribution, occurs in rivers and coastal lakes and, like other amphidromous shrimp, requires a brackish environment to complete its life cycle. The most recent studies on morphological and reproductive aspects of M. acanthurus are focused on the same geographic area, which makes knowledge of the different populations of this species still incomplete and fragmented. Morphometric analyzes were carried out in order to identify morphological sexual maturity, sexual dimorphism and relative growth patterns between males, females, juveniles and adults of a population not yet studied. For relative growth, the length of the following structures was evaluated: cephalothorax, ischium, merus, carpus, propodus, dactyl, chelipod and second pleura (females). The length of the propodus in males and the second pleura in females were the structures that best distinguished juveniles and adults. The average carapace length in males was 18.42 mm (± 6.70 mm) and in females it was 10.57 mm (± 5.67 mm). Males reach morphological sexual maturity with a carapace length of 11.80 mm and females with 9.90 mm, with sexual dimorphism in size in favor of males being identified.