Abstract
Abstract Aim The present study aimed to analyze a M. amazonicum population structure in a reservoir of the “Triângulo Mineiro”, Brazil. Methods Monthly surveys were carried out from April/2012 to May/2013 at the Miranda Hydroelectric Plant Reservoir located in Araguari river, state of Minas Gerais. A sampling section of 100 m long, 5 m wide and depth not exceeding 1 m was defined on the banks of the reservoir. Sampling consisted on two persons quickly passing a 2 mm sieves in partially submerged marginal vegetation, for one hour. The sampled specimens were identified, sexed and measured. Results A total of 2,584 specimens were analyzed, of which 64.62% were females (3.93% ovigerous, 5.94% non-ovigerous and 54.75% juveniles), 29.16% males (21.41% adults and 7.76% juveniles) and 6.22% juveniles of undetermined sex. The sex ratio (1:2.21) indicated a clear deviation for females, for the whole sampling period, monthly and for each size class. Males had an average carapace length (CL = 4.50 ± 0.71 mm) significantly lower than females (CL = 4.64 ± 1.47 mm) and the size frequency distribution revealed a unimodal pattern, with peaks occurring in 4.0 - 4.9 mm size class for males and in 3.0 - 3.9 mm size class for females. The relation between total and carapace length was significant, indicating a negative allometric growth. No males’ morphotypes were found. The population presented a continuous reproduction with a gradual increase between April and June/2012. Female sexual maturity was determined for 6.3 mm of CL, while for males was estimated for 4.0 mm. Conclusion The Miranda reservoir population had a body size variation similar to the continental populations of Pantanal. The sexual dimorphism observed may be related to the absence of male morphotypes and to the “pure search” reproduction strategy. The deviated sex ratio for females may increase the chance of fertilization and the reproductive success. The presence of juveniles and ovigerous females throughout the year indicates a continuous reproduction pattern of the population.
Highlights
Brazil’s freshwater prawn farming is world‐wide known, in continental waters is predominantly made with an exotic species - Macrobrachium rosenbergii De Man, 1879 (Palaemonidae) (FAO, 2014)
Macrobrachium amazonicum species are divided into two main populations: those living in coastal regions, which inhabit the river estuaries and depend on brackish water to complete their life cycle, and continental populations that live in rivers, lakes and other inland water bodies (Moraes-Valenti & Valenti, 2010)
In order to provide evidences for this possibility, the present study evaluated the population of Macrobrachium amazonicum in the reservoir of Miranda, describing its population structure and some morphological characteristics of the individuals as total length and caparace length
Summary
Brazil’s freshwater prawn farming is world‐wide known, in continental waters is predominantly made with an exotic species - Macrobrachium rosenbergii De Man, 1879 (Palaemonidae) (FAO, 2014). Macrobrachium amazonicum species are divided into two main populations: those living in coastal regions, which inhabit the river estuaries and depend on brackish water to complete their life cycle, and continental populations that live in rivers, lakes and other inland water bodies (Moraes-Valenti & Valenti, 2010). Variations between these populations occur regarding environmental characteristics, behavioral and life histories (Hayd & Anger, 2013), in addition to physiological and morphological characteristics (Charmantier & Anger, 2011; Boudour-Boucheker et al., 2013). These variations can be exemplified by the different osmoregulation and survival skills among larval and adult stages (Augusto et al, 2007), and changes in reproductive strategies and size reached by individuals of these continental and estuarine populations (Odinetz-Collart & Magalhães, 1994; Silva et al, 2004)
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