Abstract
This study aimed to describe the population structure of the Amazon shrimp Macrobrachium amazonicum, as well as their relative growth between the length of the cephalothorax and the total length, and between the length of the cephalothorax and the total mass of shrimps of a fluvial-estuarine plain in the State of Pará. Shrimps were sampled monthly from August 2006 to July 2007, using trawl nets, taking three replicates at each site (Arapiranga and Mosqueiro) per month, totaling 72 replicates. We caught 5,510 specimens, being 90.90% from Arapiranga Island and 9.1% from Mosqueiro Island. The highest densities occurred in July (1.33 individuals/m²), at the beginning of the dry season and in December (1.66 individuals/m²), at the beginning of the rainy season. The morphometric analysis for separate and grouped sexes resulted in negative and positive allometric growth. Ovigerous females were observed in all months, indicating continuous reproduction and the majority (67.81%) was caught during the less rainy season. The abundance and continuous reproduction of M. amazonicum show that this estuary offers conditions for the proper development of this population.
Highlights
The Amazon shrimp Macrobrachium amazonicum (Heller, 1862) occurs in various habitats, from inland waters to estuaries (OdinetzCollart, 1991)
Assessments of the population structure of shrimps are indispensable in understanding the various relationships that different populations may provide in relation to environmental conditions and this can be evaluated from changes related to growth, sex ratio and reproduction
Considering the shrimps from the two islands, the density of M. amazonicum was higher in July (1.33 ind./m2), at the beginning of the less rainy period, and in December (1.66 ind./ m2), at the beginning of the rainy season
Summary
The Amazon shrimp Macrobrachium amazonicum (Heller, 1862) occurs in various habitats, from inland waters (lentic and lotic environments) to estuaries (OdinetzCollart, 1991). This great environmental plasticity of the species has been related to intraspecific differences ranging from morphological characteristics (Porto, 2004) to genetic variations (Peixoto, 2002; Pileggi and Mantelatto, 2010; Vergamini et al, 2011) which might reflect specific conditions of survival, development, reproduction, c Published by Brazilian Crustacean Society, Ribeirão Preto, Brazil - July 2014 growth, and relationship to the environmental variables. The species can show wide variations in their population pattern with respect to various factors such as modified environmental conditions, density changes and genetic characteristics, among others (Fonteles Filho, 1989)
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