Abstract In the present study, we describe a co-infection of two microsporidians within the abdominal muscle of the Amazon River prawn Macrobrachium amazonicum from Brazil, detected through light and transmission electron microscopy and histopathological analysis. Two spore types and respective early developmental stages (meronts, sporonts, and sporoblasts) appeared grouped in numerous adjacent clusters among the muscle fibers of the host. Spores were initially divided into two morphotypes, Sp. 1 and Sp. 2, based on differences in shape, size, and internal organization. The Sp. 1 spores are pyriform to ovoid (4.3 ± 0.3 × 3.7 ± 0.4 µm in size) and resided in groups of eight within a sporophorous vesicle. Sp. 1 spores had bilayered walls and long tape-like external filaments with irregular morphology and size, forming a complex contiguous membranous system attached to the spore wall. The umbrella-like anchoring disc of the spores was in continuity with an anisofilar polar tube arranged in 7‒8 (rarely 9) coils. The Sp. 2 spores were rod-like in shape (3.1 ± 0.5 × 0.8 ± 0.1 µm in diameter) and the polar tube had 7‒8 coils. Their merogonic and sporogonic stages occurred within the sarcoplasm of the muscle cells in close contact with the myofibrils. Based on ultrastructural organization of the sporogonic stages, the Sp. 1 and Sp. 2 morphotypes probably belong to the genera Inodosporus and Myospora, respectively.

Abstract In 2012, a severe drought struck the southeastern of Brazil compromising the Paraná River Basin reservoirs. Here, we described how this climatic event promoted a massive mortality of the giant freshwater mussel Anodontites trapesialis in Furnas reservoir and reported the consequences of this phenomenon. In November 2012, three quarters of 100 m2 were sampled in this reservoir, where 812 dead shells of A. trapesialis were analyzed and measured (33 ˫ 133 mm). The species showed an aggregated distribution with high density ( X ¯: 1.0 - 5.5 ind/m2). Despite the massive mortality detected in field, it was possible to find living specimens in a small channel in the studied area, allowing the species to survive the water level fluctuations. Large adult individuals (100 ˫ 124 mm) were more affected by drought than juveniles, accounting for about 90% of the dead mussels analyzed. Two years after the massive mortality event, water level was not reestablished and a terrestrial succession (with elevations in the concentration of organic matter and calcium in sediment) was observed in the studied area. We verified that the damming associated with extreme climatic events affect negatively the populations of A. trapesialis and should be faced as a conservationist problem.

Abstract The size at the onset of sexual maturity (SOM) was determined in four hololimnetic populations of Macrobrachium amazonicum using morphometric, physiological and functional criteria. Male prawns from two populations analyzed had hypertrophied chelipeds and large body proportions, showing the presence of four morphotypes, i.e. large-size phenotype (LS). However, the other two populations showed smaller males without morphotypes, i.e. small-size phenotype (SS). The development of sexual weapons in males modulated the mating system and SOM in this species. It was verified that there is a synchrony between physiological and functional maturities in SS males. On the other hand, functional maturity in LS males occurred after physiological and morphological maturities. In females, we verified synchronization between morphological and functional maturities. The results obtained indicated that, in both sexes, physiological maturity anticipates the others criteria. There were no differences between the sequential scheme of sexual maturity for female phenotypes, being: physiological → functional morphological. However, the evaluation of sexual maturity in males must take into account the phenotype of population, since that was modulated by functional maturity. The sequential scheme for LS males is: physiological → morphological → functional, while for SS males it is: physiological = functional → morphological.

ABSTRACT Population biology, growth and reproductive aspects of the amphidromous shrimp Palaemon pandaliformis (Stimpson, 1871) were investigated in a Neotropical river of northeastern Brazil. The specimens were collected every month from September 2009 to August 2010. Total and monthly sex ratios deviated in favour of males. Von Bertalanffy growth parameters indicated that the females grew more rapidly, reached larger sizes, and had a longer life span than males. We also observed continuous reproductive activity and juvenile recruitment throughout the year. Relations between the number of eggs (fecundity) and body size indicated that fecundity in females increase with size. Compared with previous results, some population biology parameters of the freshwater population of P. pandaliformis differ from estuarine populations. The reproductive aspects analyzed here and their comparison with other marine species were consistent with the hypothesis that Palaemonidae species are undergoing an adaptation process and colonizing fresh water environments.