Population structure, mortality, and recruitment of Macrobrachium amazonicum (Heller, 1862) (Caridea: Palaemonidae) in the eastern Amazon region, Brazil

Abstract

Macrobrachium amazonicum (Heller, 1862) displays marked ecological plasticity as it is found in a variety of freshwater environments, from inland waters to estuaries. We analyzed a population located in the eastern Amazon region in northern Brazil. At the study site, Parananema Lake, Parintins, Amazonas state (02°40'52"S, 56°47'15"W), the species completes its life cycle in a freshwater environment influenced by the dynamics of the Amazon River. In addition to describing the population structure, this study examined data on the mortality, recruitment, and sex ratio of the population. Data were collected between March 2013 and February 2014, during which 1,300 individuals were sampled, including 386 males and 911 females (of which 155 were ovigerous). No significant difference in the mean sizes of males and females was found, and females outnumbered males in every month of the collection period. The results indicate that M. amazonicum reproduces continuously throughout the year at the study site. Peaks of different magnitudes were observed in the population size of this demographic group, with the largest occurring during the river's low-water season. These reproductive pulses resulted in bimodal monthly histograms occurring precisely in months following the observed recruitment modes. The females in this location reached maturity while they remain small in size. The smallest ovigerous female measured 5.1 mm (CL), which may be related to rapid gonadal development or extreme environmental conditions. Mortality analyses indicate that the species is not being overexploited locally, meaning that the obtained results and values were not affected by pressure from fishing. Our results confirm the existence of variations between estuarine and inland populations of M. amazonicum and indicate that the dynamics of the Amazon River, which is unique in its size and water volume, influences the life-cycle strategies of the species in the study area.

Population structure of Macrobrachium amazonicum (Heller, 1862) (Decapoda: Palaemonidae) in Miranda Hydroelectric Plant Reservoir, Araguari river, Minas Gerais, Brazil

“…The sex ratio observed in the present study showed that the population was not stable in relation to the expected theoretical ratio of 1:1, since a favorable proportion to females occurred both monthly and in size classes, except in 5 -5.9 mm size class. This favorable proportion of females in M. amazonicum was also verified in several studies (Odinetz-Collart, 1987;Hayd & Anger, 2013;Taddei et al, 2017) although Silva et al (2002a, b) found dominance of males. Skewed sex ratios are widely diffused among crustaceans and are influenced by differences between males and females related to seasonal migrations, birth rates, mortality, longevity and predation (Wenner, 1972).…”

Morphometric differences between two exotic invasive freshwater caridean species (genus Macrobrachium)

“…The absence of such morphotypes is more common in populations in which individuals show an aggregate distribution, as it occurs in muddy environments (Pantaleão et al 2012), with a great abundance of food and females. This may decrease intraspecific competition (Taddei et al 2017b), as seen for the individuals addressed here.…”

“…The reproductive biology of M. amazonicum and M. jelskii was previously investigated from other Brazilian regions: Scaico (1992) and Da Silva et al (2004) to the North-eastern; Odinetz-Collart and Magalhães (1994), Lima et al (2014) and Taddei et al (2017b) to the Northern; Hayd and Anger (2013) to the Midwestern; Bialetzki et al (1997) to the Southern; and Pantaleão et al 2012and Barros-Alves et al (2012) to the Southeastern. These studies suggest that each species present a certain level of reproductive plasticity, that is the same species showed different reproductive aspects, which vary according to the studied area.…”

Ovarian development and spawning of Macrobrachium amazonicum (Crustacea, Decapoda)

“…Porto & Santos (1996) found a discontinuous (reproduction) spawning period for the shrimp Farfantepenaeus subtilis (Pérez-Farfante, 1967) collected from an island in the state of Maranhão (Brazil), and two separate spawning events suggesting biannual total spawning. Macrobrachium amazonicum has continuous reproduction (see Collart, 1991;Bialetzki et al, 1997;Lucena-Frédou et al, 2010;Freire et al, 2012;Bentes et al, 2016;Taddei et al, 2017) confirming the parceled spawning for this species. Sampaio et al (2007), when examining M. amazonicum collected from a river in the state of Ceará (Brazil), not only found continuous reproduction but also ovigerous females with gonads in different developmental stages.…”