Biologia populacional de Macrobrachium jelskii (Miers, 1877) no açude Laranjeiras, município de Cruz das Almas, estado da Bahia

Abstract

In Brazil, there are 18 species of Macrobrachium, some of them are important economically, however, others are commonly used as lures in angling, food for the riverine population, and compose an important part of the trophic web in limnic environment. Commonly known as “camarão sossego” (quiet shrimp) in most of the Brazilian territory, Macrobrachium jelskii (Miers, 1877) is widespread in the country and it is found in almost all South America. The knowledge of the population structure and reproductive biology of M. jelskii (Miers, 1877) is an important tool for the creation of management strategies for a better use of this natural resource, and may also serve as the basis for the development of new research in the areas of ecology, fisheries biology, and conservation policy. The goal of this study was to elucidate the population structure and reproductive biology of this species. The specimens were collected using sieves in Laranjeiras pond, located in an urban area in Cruz das Almas, Bahia, from February/2013 to January/2014. The sex of the animals collected was determined in laboratory and their total length was measured as well as the shell and abdomen length. In addition the following parameters were determined: the wet weight, size and volume of eggs, and fecundity. A total of 1,723 specimens were collected. Females (n = 1,011) outnumbered males (n = 712), resulting in a sex ratio of 1.4:1. The carapace length ranged from 3.58 mm to 11.68 mm for females and from 3.3 mm to 10.21 mm for males. The weight ranged from 0.05 – 0.74 g for the males and from 0.06 – 0.78 g for females, with mean values of 0.25 and 0.42 for males and females, respectively. Statistical analysis showed that females reached greater size and weight than the males, indicating a sexual dimorphism. The smallest individuals were observed in February, April, May and November. From the 1,011 females found, 229 were ovigerous with carapace length ranging from 5.96 to 10.80 mm and the total weight ranging from 0.17 to 0.70 g. Fecundity ranged from 5 to 56 eggs (mean = 25.19 eggs per female). Ovigerous females were found during the entire sampling period, with a higher concentration during March/2013, characterizing a continuous reproductive period. Fecundity showed a direct relation with the total length of specimens and the egg loss was equal to 4.5%. Eggs showed green color and elliptic form, characterized by significant differences in the length of the major and minor axes. Additionally, there was a significant difference in the egg volume during embryonic development.