Distribution and growth in adults of Macrobrachium acanthurus Wiegmann, (Decapoda, Palaemonidae) in a tropical coastal lagoon, Brazil

Abstract

Macrobrachium acanthurus Wiegmann, 1836 is a Palaemonidae commonly found in Brazilian coastal environments. At Imboassica lagoon, located in the north of the State of Rio de Janeiro, it is found in two stages of its life cycle: as larvae and as reproductive adults. This work had as its goal the evaluation of adults distribution, estimating the weight/length relationship and the condition factor of these adults. After sampling in two regions of the lagoon, one interior and another closer to the ocean, we verified that females are found in a greater proportion close to the ocean, and males are found in greater number in the innermost region, amidst the aquatic macrophytes, suggesting that the fecundation takes place in this last area and the females then travel to the area closer to the ocean to spawn. Total and carapace weight/length relationship exhibited differences between males and females, presenting positive allometric growth. The relative growth of the cephalotorax related to total length showed that it correspond to 53% of the total length in females, and 50% in males. The average condition factor was significantly lower than the expected pattern, demonstrating that the species does not find ideal conditions in the lagoon. This may be attributed to the migration of the adults, to the spawning and/or to the impact caused by the frequent sandbar openings that took place at Imboassica lagoon during the studied period.