Estrutura populacional e biologia reprodutiva de Macrobrachium jelskii (Miers, 1877) em um açude artificial do município de Cruz das Almas-BA

Abstract

Macrobrachium jelskii (Miers, 1877) known in Brazil as “camarão sossego” is widely distributed in lotic and lentic environments from Central and South America. Studies on population biology of decapod crustaceans are an important foundation to subsequent studies on ecology, fishery and conservation. The aim of this study was to determine the population structure, sex ratio and reproduction pattern of a population of M. jelskii from Cruz das Almas, Bahia, Brazil. Samples were collected monthly from August 2011 to March 2012 using hand nets. In laboratory animals were sexed and measured (total length, carapace length and abdomen length) and weighed. The number of eggs of each ovigerous females was counted and the size and volume of eggs were taken. A total of 1,563 specimens were collected of which 527 were males (34%) and 1,036 were females (66%), resulting in a sex ratio equal to 0.51 : 1. The carapace length ranged from 3.21 to 8.13 mm in males and 3.01 to 11.18 mm in females. Statistical analysis showed that females were larger than males (U = 167x105, p < 0.001). The size class distribution of carapace length were unimodal and bimodal for males and females, respectively. Macroscopic analysis of the gonads revealed six distinct development stages, and ovarian maturation began when females reached 5.01 |— 5.5 mm size class, but the smallest ovigerous female measured 6.86 mm. Females with maturing ovarians or eggs attached to the pleopods were found throughout the entire sampling period, with greater concentration in December 2011; such characteristics are typical of continuous reproductive pattern. The number of eggs per female was directly proportional to the carapace length and wet weight of the animals and mean number of eggs calculated were 24 (± 6.8) with an egg loss percentage equal to 17%. Eggs were green and elliptical in shape, since significant differences were found between sizes of the major and minor axes. In addition, there was significant increase in the volume of eggs during embryonic development.