During downstream transport from rivers to estuaries, early larval stages of the Amazon River prawn Macrobrachium amazonicum (Heller 1862) are likely exposed to planktonic food limitation. In the laboratory, we studied the effects of presence or absence of food on larval survival, moulting and biomass (dry mass, and content of carbon, hydrogen and nitrogen). Unfed larvae developed successfully from hatching of the Zoea I (Z I) to the third zoeal stage (Z III). Complete absence of starvation effects indicated obligatory lecithotrophy in Z I, while significantly delayed moulting and reduced biomass in unfed Z II proved that this stage is facultatively lecithotrophic. Although unfed Z III did not develop any further (obligatory planktotrophy), they still showed a high endotrophic potential, surviving for up to another 10 d (in total 2 wk from hatching), and utilizing about two-thirds of their initial biomass. Dramatically decreasing C:N ratios in unfed larvae suggest an almost complete metabolic degradation of internal lipid stores (visible as fat droplets in the hepatopancreas region), but little protein mobilization. Larvae obtained from 2 different females differed significantly in biomass at hatching and, correspondingly, also in maximum survival time, delay of moulting to the Z III and average rates of biomass utilization. In conclusion, the early larval stages of M. amazonicum depend very little on food, shifting from completely non-feeding behaviour (Z I) through facultative lecithotrophy (Z II), to planktotrophy (later stages). This ontogenetic pattern may be an adaptation to initial food limitation associated with larval export from limnic to estuarine environments.

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The palaemonid shrimp Macrobrachium amazonicum (Heller 1862) lives in coastal rivers and estuaries along the northern coasts of South America as well as in inland waters of the Amazon, Orinoco, and upper La Plata (Paraguay-Paraná) River systems. In an experimental investigation on a little known, hydrologically isolated population from the Pantanal (upper Paraguay basin), we studied ontogenetic changes in early larval feeding and growth. Similar to a previously studied population from the Amazon estuary, the first zoeal stage (Z I) hatched with conspicuous fat reserves remaining from the egg yolk. While Z I is a non-feeding stage, Z II is facultatively lecithotrophic, and Z III is planktotrophic, requiring food for further development. Compared to estuarine larvae, those from the Pantanal hatched with lesser amounts of lipid droplets, and they survived for significantly shorter periods in the absence of food (maximally 8-9 d versus 14-15 d, at 29°C). Both populations moulted in short intervals (ca. 2 d) through larval stages Z I to VI. Biomass increased exponentially, with a higher growth rate observed in the Pantanal larvae. These develop in lentic inland waters, where high productivity allows for fast growth of planktonic predators. By contrast, the early larval stages of the Amazon population show a higher endotrophic potential and are thus better adapted to conditions of food limitation occurring during riverine downstream transport through lotic waters, towards coastal marine habitats. Initial larval independence from food in the Pantanal clade is interpreted as a plesiomorphic trait persisting from coastal marine ancestors. KEY WORDS: Caridean shrimp · Larval feeding · Larval growth · Lecithotrophy · StarvationResale or republication not permitted without written consent of the publisher Aquat Biol 9: [251][252][253][254][255][256][257][258][259][260][261] 2010 guay and Paraná River basins (La Plata system), are hydrologically separated and thus genetically completely isolated from all others.The occurrence of Macrobrachium amazonicum in the La Plata system has occasionally been considered to be the result of a recent anthropogenic introduction (Bialetzki et al. 1997, citing a technical report by Torloni et al. 1993). In a recent review, Maciel & Valenti (2009) also cited Magalhães et al. (2005) in this context. However, this reference is based on a misunderstanding of a statement, where Magalhães and coauthors are actually saying (p. 1933) that M. amazonicum was probably introduced into water reservoirs and rivers of the northeastern and eastern states of Brazil (citing Ramos-Porto & Coelho 1998), while the populations in the La Plata basin are explicitly referred to as belonging to the 'native fauna ' (cf. Holthuis 1952). This is in fact strongly corroborated by much earlier records from northern Paraguay (dating back to A. Borelli's expedition in 1893-94, published by Nobili 1896) and from the Pantanal of Mato Grosso, southwestern Brazil (Moreira 1912(Moreira , 1913.Due to hydrological frag...

The palaemonid shrimp Macrobrachium amazonicum shows an unusually large geographic range (ca. 4 000km across) living in coastal, estuarine, and limnic inland habitats of the upper Amazon, Orinoco, and La Plata basins. This raises doubts whether allopatric, ecologically diverse populations belong to the same species. While shrimps from estuarine and Amazonian habitats have been studied in great detail, very little is known about hololimnetic inland populations. In the present study, biological traits related to growth (maximum body size, fresh weight, morphometric relationships) and reproduction (sex ratio; occurrence of male morphotypes; minimum sexable size; minimum size of ovigerous females; fecundity; egg size), were studied in M. amazonicum collected from a pond culture and two natural freshwater habitats (Rio Miranda; Lagoa Baiazinha) in the Pantanal of Mato Grosso do Sul, Brazil. In total, 2 270 shrimps were examined (603 males; 1 667 females, 157 of these ovigerous). Sex ratio (males:females) was at all sampling sites strongly female-biased, ranging from 0.2-0.6. Maximum body size was larger in natural habitats compared to the pond culture, suggesting reduced growth or a shorter life span under artificial mass rearing conditions. Maximum fecundity observed in our material was 676 eggs, reached by the largest female (TL=65mm; Lagoa Baiazinha). A significant difference between slope parameters of linear regressions describing fecundity, either in terms of numbers of eggs laid or of larvae released, in relation to female fresh weight, indicates egg losses. This may be due in part to a 2.4-fold increase in egg volume occurring during the course of embryonic development, while the available space under the abdomen remains limited. Size-weight relationships differed significantly between males and females, indicating sexspecific morphometric differences. Males appear to have a more slender body shape than females, reaching thus lower weight at equal TL. When reproductive and morphometric traits are compared with literature data from estuarine and inland populations living in the Amazon and Orinoco plains, shrimps from the Pantanal show conspicuous peculiarities differing from other populations: (1) maximum body size is far smaller, suggesting shorter longevity; (2) females are consistently larger than males; (3) different male morphotypes are absent; (4) minimum sexable size and (5) minimum size of ovigerous females are smaller. These traits suggest a heterochronic shift (predisplacement) of sexual maturation and r-selection. In summary, our data show biologically relevant differences in life-history traits of shrimps from the Pantanal compared to M. amazonicum populations in other regions. All these differences persist also in long-term cultures maintained under constant conditions. Altogether, our data support the hypothesis that M. amazonicum in the Paraná-Paraguay drainage basin has phylogenetically diverged from allopatric populations that are hydrologically separated by continental watersheds, implying an ...

Biofloc technology system (BFT), recirculation aquaculture system (RAS) and polyculture promote efficient use of water, area and nutrient recycling, which are essential practices for sustainable aquaculture development. The aim of this study was to evaluate the growth, feed efficiency, biofloc composition and water quality of Nile tilapia Oreochromis niloticus (Linnaeus, 1758) in monoculture and polyculture with giant freshwater prawn Macrobrachium rosenbergii (De Man, 1906) in BFT and RAS, over a period of 30 days. Fish (n = 128; 7.29 ± 0.67 g) were distributed randomly in 16 experimental tanks (8 fish/tank). Prawn (n = 96; 0.50 ± 0.09 g) were allocated in 8 experimental tanks (12 prawn/tank) in a polyculture. The experimental design was completely randomized with four treatments with four replicates each, in a factorial design 2 9 2 (BFT and RAS vs. monoculture and polyculture). The experimental diet (28% of digestible protein; 3100 kcal kg-1 of digestible energy) was used both to fish and prawn in BFT and RAS. There was significant effect (p \ 0.01) of the system and the culture for weight gain, apparent feed conversion and protein efficiency ratio. The average weight gain and apparent feed conversion of tilapia in monoculture (30.04 g and 1.39) and in polyculture (36.44 g and 1.27) were superior (p \ 0.01) in BFT than in monoculture (23.64 g and 1.74) and in polyculture (24.14 g and 1.61) in RAS. Weight gain and survival of giant freshwater prawn was superior (p \ 0.01) in BFT (0.43 g and 87%) compared to RAS (0.26 g and 79%). The data showed that BFT provides better growth performance responses in monoculture for Nile tilapia and in polyculture with giant freshwater prawn compared to RAS.

The neotropical species Macrobrachium amazonicum (Heller, 1862) is considered a particularly successful species, showing an extremely wide range of distribution (ca 4.000 km across). Populations assigned to this species live in estuaries along the northern and northeastern coasts of South America as well as in fresh water habitats in the Amazon, Orinoco and Paraná-Paraguay river basins. Following recent comparative studies that showed differential ecological, reproductive, developmental and physiological traits in geographically separated populations from the Amazon delta and the Pantanal region, Brazil, we examined the morphology of adult shrimps from these two regions. Based on significant differences, we conclude that the Pantanal population constitutes a new species, which is described here as Macrobrachium pantanalense. The main differences between M. amazonicum and the new species have been found in the morphology of the second pereiopod, the telson, and in the color patterns of both males and females. A modification on the key of American species of Macrobrachium is provided to accommodate the new species.

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The river prawnMacrobrachium amazonicumHeller, 1862 occurs in limnic and brackish habitats in northeastern South America, with a broad distribution range and a wide phenotypic variability. Recently, representatives of populations from the Pantanal were reassigned to the newly described speciesM. pantanalenseDos Santos, Hayd & Anger, 2013, according to distinct morphology, life-history, and geographic distribution. Genetic distinctness is in a range that may be recognized as either inter- or intraspecific, which raises the question to what extent genetic distance data alone should be used to determine whether two closely related populations belong to the same or different species. Here, we discuss the case ofM. amazonicumand compare it with other cases of conflicting conclusions from studies on decapod crustaceans, mainly using morphological or genetic criteria. Based on these comparisons, we caution against a too simiplistic view of genetic distance as an exclusive criterion for the definition of “species” vs. “conspecific populations”.