Macrobrachium amazonicum is a native freshwater shrimp from the northern region of Brazil, widely distributed throughout the Amazon basin, which supports an extensive regional fishery. Here, we assessed its dietary habits in the wild in a prime fishery area for this species in the lower Amazonas River (Pará state, Brazil) and evaluated the relative efficiency of three bait types (cooked rice, canned sardines, and babassu fruit meal) for both its quantitative and qualitative capture yield. Stomach contents were analyzed using occurrence frequency, the point method, and the food index. We identified four food categories: fine particulate organic matter (FPOM), coarse particulate organic matter (CPOM), particulate plant matter (PPM), and identified plant matter (INV) (leaves, root remains, and invertebrates). According to the frequency of occurrence and the point method, fine particulate organic matter (FPOM) was the most important food category (88%). In the bait attractiveness test, the average number of shrimps and total biomass captured varied significantly among treatments, with babassu flour being the most attractive. Our results indicate that M. amazonicum is omnivorous and an opportunistic generalist shrimp, and that among the three baits tested, babassu meal likely renders higher yields.

ABSTRACT Length–mass regressions are widely used to estimate the biomass of aquatic organisms through allometric formulas, as they provide a rapid and efficient alternative to direct measurements. Developing species-specific allometric equations facilitates biomass estimation and supports ecological assessments. This study developed length–mass relationships for the non-native shrimps Macrobrachium pantanalense Santos et al. 2013 and Macrobrachium amazonicum (Heller, 1862) in a large reservoir in southeastern Brazil. In April 2024, we sampled 192 M. pantanalense and 58 M. amazonicum individuals across four sites. Body dimensions—(i) body length and (ii) cephalothorax length – were measured using a stereomicroscope and ImageJ software. Biomass was quantified as ash-free dry weight after drying specimens for 48 h at 60°C and incinerating them for 4 h at 550°C. Power functions (DM = aLb) were used to derive length–mass regressions. Cephalothorax length was the best predictor of biomass for both species, explaining most of the variance in M. pantanalense (r2 = 0.86, b = 3.08) and M. amazonicum (r2 = 0.58, b = 1.62), indicating isometric and negative allometric growth, respectively. Overall, cephalothorax length proved to be a robust and practical metric for biomass estimation, providing useful equations for ecological monitoring and management of non-native shrimp populations.

ABSTRACT This study aimed to assess the presence of microplastics (MPs) in the gills of Macrobrachium amazonicum shrimp, identifying the most abundant categories (type, shape, degradation level, and color), and testing if there is a significant difference in the mean number of MPs among demographic classes, size classes, and collection months. Shrimps were collected between August 2021 and March 2022 from the Funil Hydroelectric Power Plant reservoir in Minas Gerais, Brazil. Each specimen was sexed, measured, and had its gills dissected. MPs were visually identified, categorized, and counted under a microscope. A total of 4,808 MPs were obtained with the most abundant microplastic being fiber, elongated, degraded, and transparent. Juveniles had the lowest mean number of MPs, being significantly different from the others (p-value = 1.289e-08). Results from the size classes supported these findings, as smaller individuals had a lower average of MPs. Temporal analysis showed variation throughout the months: November and December had the lowest contamination levels, while February had the highest. These findings suggest potential temporal fluctuations in environmental MP exposure. The observed patterns may have long-term implications, as MP accumulation could affect the health of M. amazonicum, a species of significant ecological and economic importance.

Herein, we describe multiple occurrences of morphological abnormalities in Macrobrachium amazonicum (Heller, 1862) collected in a hypertrophic urban river that flows through the city of Belém, Pará State, Eastern Amazonia, Brazil. The samples were performed between 2022 and 2025, using traditional local traps called “matapi” placed in shallow areas of the Guamá River (01°27’54.2”S; 048°26’02.6”W). After sampling, all individuals were transported to the Laboratório de Crustáceos (LabCrus/UFRA) where they were identified, sexed, measured, and only the anomalous specimens were photographed. A total of 4,830 individuals of M. amazonicum were collected, of which 54 (8 males and 46 females), corresponding to 1.12% of the total, showed abnormalities. The deformities were observed in the rostrum (68.5%) and in the telson (31.5%). The highest incidence of abnormal females was observed in May and June 2022, with other peaks in March and August 2023; while for males, the highest presence of abnormalities was in August 2025. The Guamá River receives heavy inflows of urban and industrial effluents, which may be one of the causes of the anomalies observed in M. amazonicum. However, other conditions may be associated with these anomalies, such as nutritional or genetic factors. This study increases the knowledge on morphological abnormalities in shrimps, especially in M. amazonicum, and highlights the need for biological and environmental monitoring along the main urban river (Guamá River) in the city of Belém, Pará.

Microplastic impacts physiological mechanisms of marine, diadromous, and freshwater crustaceans.

Background/Objectives: The selection and validation of species-specific housekeeping genes (HKGs) have become increasingly common in functional genomics, with application of quantitative Polymerase Chain Reaction (qPCR) or cDNA-based qPCR (RT-qPCR). Despite the Macrobrachium amazonicum having RNA-seq studies available, there are still no data on the most stable and consistent HKGs for use in relative gene expression analyses. Therefore, the present study aimed to identify and validate seven HKGs in M. amazonicum: Eukaryotic Translation Initiation Factor (EIF), 18S ribosomal RNA (18S), Ribosomal Protein L18 (RPL18), β-actin, α-tubulin (α-tub), Elongation Factor 1-α (EF-1α), and Glyceraldehyde-3-phosphate Dehydrogenase (GAPDH). Methods: The HKGs were identified in the M. amazonicum transcriptome, characterized for identity confirmation, and compared against public databases. Subsequently, RT-qPCR assays were prepared using muscle, hepatopancreas, gills, testis, androgenic gland, and ovary to assess the stability of the HKG markers, employing the comparative ∆Ct, BestKeeper, NormFinder, and GeNorm methods. Results: All candidate HKGs identified showed high similarity with other decapods. Reactions performed with these markers demonstrated high specificity, PCR efficiency, and elevated coefficients of determination. The comprehensive ranking, indicated that no single HKG was stable across all tissues, with HKGs showing the best stability being tissue-specific. The most stable HKGs were RPL18 and 18S. GAPDH, historically used as an HKG, showed the poorest performance in stability ranking for most tissues tested, whereas β-actin was most suitable only for ovarian. Conclusions: These data reinforce the need for species-specific HKG validation and provide an appropriate panel of reference markers for gene expression studies in the M. amazonicum.

The present study evaluated the phylogenetic relationships and the population structure in the ‘Macrobrachium amazonicum’ species complex, including M. amazonicum and M. pantanalense based on Single Nucleotide Polymorphism (SNP) markers. We analyzed specimens from three main genetic lineages (Clade I: M. amazonicum – Santarém-PA; Clade III: M. amazonicum – Mosqueiro-PA; Clade II: M. pantanalense – Bela Vista de Goiás-GO) and one artificially isolated population (M. amazonicum – Tucuruí-PA). After ddRAD sequencing, a final set of 969 SNPs were genotyped for all populations/species. High levels of genetic structure were observed among the populations of M. amazonicum, particularly when individuals from inland freshwater habitats in Amazon were compared to those from coastal basins, reinforcing the morphophysiological differences among both groups. Moreover, differently from the phylogenetic inferences using mitochondrial DNA markers, all analyses by SNPs confirmed the taxonomic status of M. pantanalense as a distinct species from M. amazonicum. Therefore, we provided the first molecular evidence of speciation in this group, being useful to resolve the taxonomic uncertainties in M. pantanalense. This study also indicates a putative process of ongoing speciation involving the clades I and III of M. amazonicum, thus emphasizing the need for further studies to better assess the relationships between both lineages.Supplementary InformationThe online version contains supplementary material available at 10.1038/s41598-025-17666-y.

The shrimp Macrobrachium amazonicum (Heller, 1862) is a widely distributed native species in South America. This study presents an updated geographic distribution of the species through a systematic review of primary and secondary data, as well as reports of new native and non-native occurrences. The distribution extends approximately 4976 km, from the Maracaibo hydrographic ecoregion (Venezuela) to Lower Paraná (Argentina), between the latitudes 10°40’37”N and 27°20’31”S, and about 5226 km, from the Tuira River (Panama) to the Northeastern Atlantic hydrographic region (Rio Grande do Norte, Brazil), between the longitudes 79°31’30”W and 35°12’7”W. Covering much of South America and 2 hydrographic ecoregions in Panama, geographic expansion was detected with new continental and coastal records, both in native and non-native areas. New occurrences were recorded in the hydrographic ecoregions of Gurupi (Maranhão, Brazil); Lower Piranhas-Açu (Rio Grande do Norte, Brazil); Middle São Francisco (Bahia, Brazil); Upper Tocantins (Goiás, Brazil); Middle Paraguay (Mato Grosso do Sul, Brazil); Tarauacá (Amazonas, Brazil); Maracaibo, Trinidad, and Orinoco (Venezuela); Magdalena-Sinu (Colombia); Chagres (Panama); and the High Andes of the Amazon (Bolivia). The new record in Maracaibo extended the species’ range by 361 km to the north, and in Chagres, Panama, in Central America, by 51 km to the west. M. amazonicum exhibited the neotropical distribution which was already known for the species. Evidence of anthropogenic introduction in Brazilian reservoirs is supported by the absence of records in connection sites with the Orinoco and Amazon basins, which are geologically separated from the La Plata basin. The wide distribution of the species highlights its high adaptability to various environments.

Microplastics in a tropical lentic environment: dynamics between sediments and the shrimp Macrobrachium amazonicum

Introduction: Macrobrachium amazonicum is a species of shrimp native to South America, widely distributed and exploited by artisanal fishermen in the North of Brazil. Objective: This study aimed to analyze the population structure of M. amazonicum, with an emphasis on sex ratio, frequency distribution of male and female size, also considering the rainy and dry period in the study areas. Methods: For this, monthly collections were carried out from May 2017 to April 2018 with the help of “matapis” in two locations, Mazagão and Ilha das Marrecas. Results: A total of 6 796 (4 163 females and 2 633 males) were captured, with a monthly average of 531.66 specimens. The sex ratio in both areas was favorable to females with 1.32♀ : 1♂ (x² = 76.58, p < 0.001) in Mazagão and 2.34♀ : 1♂ (x² = 394.26, p < 0.001) in the Ilha das Marrecas. In both Mazagão and Ilha das Marrecas, abundance was strongly related to precipitation. Conclusions: The shrimps of Ilha das Marrecas were longer than those caught in Mazagão. Despite this fishing pressure in Mazagão, the areas proved to be favorable for the growth of the species.

Aquaculture plays a crucial role in meeting the needs of a growing human population and achieving the sustainable development goals outlined in Agenda 2030. However, it is essential that this sector grows sustainably. In this study, we hypothesized that environmental sustainability decreases as the trophic level of farmed species increases and that it is higher in integrated systems compared to monocultures. To test these hypotheses, we conducted a comparative analysis of the environmental sustainability indicators of some aquaculture systems, including the farming of primary producers, filter feeders, and low-trophic phagotrophs. We compiled secondary data on eighteen environmental sustainability indicators from seven aquaculture systems. Five are monocultures, including the farming of macroalgae (Hypnea pseudomusciformis), oysters (Crassostrea gazar) in a tropical environment, oysters in a subtropical environment, as well as tambatinga (hybrid Colossoma macropomum × Piaractus brachypomus) and tambaqui (Colossoma macropomum). Additionally, two are integrated systems: tambaqui raised in hapa nets (small cage-like enclosures) within Amazon river prawn (Macrobrachium amazonicum) ponds, and tambaqui and prawns cohabitating freely in the same ponds. A benchmark tool was utilized to establish reference values for comparing indicators between the systems, and a method was developed to create environmental sustainability indices that integrate all indicators. Environmental sustainability tends to decrease as trophic levels rise, supporting the initial hypothesis. However, the data revealed that Integrated Multi-Trophic Aquaculture (IMTA) systems ultimately have lower environmental sustainability than monocultures, which was contrary to our expectations. Algae and oyster farming were found to be more environmentally sustainable than low-trophic fish farming systems. Among these, the integrated systems did not demonstrate significantly greater sustainability than the monocultures, as initially anticipated. To gain a comprehensive understanding of sustainability, further research on the social and economic sustainability of these systems is necessary.

Third-stage larvae of a nematode species were found encapsulated in the cephalothorax of Macrobrachium amazonicum from the Guamá River, municipality of Belém, in the state of Pará, northern Brazil. Of a total of 120 specimens of M. amazonicum that were caught, 15.8% were parasitized with Cystidicolidae larvae that had morphological characteristics compatible with the genus Pseudoproleptus, such as rounded cephalic end, two pseudolips, slit-shaped buccal opening with four large submedian lips, vestibule with prostom and conical tail with a small mucron. The low presence of Pseudoproleptus larvae did not affect the growth of the shrimp, but these results cannot be generalized since the sampling was relatively low. Therefore, so the occurrence of this nematode could still negatively affect the growth and reproduction of these shrimp, leading to their death, which could directly affect their population dynamics and consumption by the Amazonian riverside population. Finally, we recommend more analyses with a greater sampling effort.

Abstract In aquatic environments, the presence of biological relationships occurring in different levels of the trophic chain is widely observed and reported in the literature, especially for invertebrates using other organisms as temporary or definitive hosts. These relationships are types of symbiosis, classified as parasitism, mutualism, or commensalism. The last frequently occurs in Platyhelminthes, including the symbiotic flatworm genus Temnocephala Blanchard, 1849, that are observed living on aquatic invertebrates and vertebrates in Central and South America. However, despite an extensive list of symbiotic relationships recorded for species in this genus, no Temnocephala species has ever been reported as an ectosymbiont of Amazon prawns. Herein we report the first occurrence of Temnocephala sp. adhered to Macrobrachium amazonicum (Heller, 1862) and Macrobrachium surinamicum Holthuis, 1948, collected in the Brazilian Amazon. The prawn species and their ectosymbionts were collected in the Guamá River (01°27’54.2”S 048°26’02.6”W), between May and September 2023, using a local trap called “matapi”. We examined 108 specimens of M. amazonicum and 24 individuals of M. surinamicum; the prevalence for Temnocephala sp. was 12.96% and 16.67%, respectively, covering between one and three symbiotic flatworms per prawn. In addition, we discuss the temnocephalan/host interaction, and provide a list of Brazilian records of Temnocephala spp. on crustacean hosts.

Our work provides a checklist of freshwater decapods (Brachyura and Caridea) from the Parnaíba river basin, Brazil, based on field collections carried out between 2018 and 2020. Eight species were collected at 30 sampling sites in the main river channels, streams, and ponds throughout the upper, middle, and lower regions of the Parnaíba river basin. The species of shrimp reported herein are Atya gabonensis (Gibiel, 1875) (Atyidae), Macrobrachium amazonicum (Heller, 1862), Macrobrachium brasiliense (Heller, 1862), Macrobrachium jelskii (Miers, 1778), and Macrobrachium olfersii (Wiegmann, 1836) (Palaemonidae), while crab species reported are Goyazana castelnaui (H. Milne-Edwards, 1853), Sylviocarcinus pictus  (H. Milne-Edwards, 1853) (Trichodactylidae), and Kingsleya parnaiba Pralon, Pinheiro & Santana, 2020 (Pseudothelphusidae). The record of Macrobrachium brasiliense is the first for the Parnaíba river basin. The knowledge of the diversity of freshwater decapod fauna can contribute to the conservation of species and their habitats.

Background: Macrobrachium amazonicum is an opportunistic and omnivorous species that primarily feeds on plant material. Recent studies have shown that Endo-β-1,4-glucanase and Endo-β-1,4-mannanase are expressed in the transcriptome of adult specimens, while juveniles are capable of digesting nutrients from purified cellulose in their diet. In organisms that degrade raw plant material, laccase plays a key role in oxidizing phenolic compounds found in lignin, leading to its depolymerization and increasing access to cellulose and hemicellulose microfibrils. Objective: In this study, we conducted an in silico identification and characterization of the laccase-encoding gene, as this enzyme is linked to lignin biodegradation in herbivorous crustaceans. Methods: We analyzed the transcriptomes of the hepatopancreas from adult M. amazonicum, sequenced using the Illumina HiSeq 2500 platform. Subsequently, bioinformatics analyses were conducted to predict the conserved regions and active sites associated with laccase activity. Results: A complete open reading frame (ORF) of the laccase protein was identified in all datasets, comprising 609 amino acids. The top 40 similarity hits corresponded exclusively to crustaceans such as prawns, crayfish, and crabs (86.3–51.4%), while the highest divergence was observed in relation to fungi, plants, and bacteria. Three conserved domains were detected, along with the complete set of copper-binding centers (T1Cu, T2Cu, and T3Cu). A notable variable residue was methionine, suggesting a reduced redox potential in M. amazonicum laccase. Conclusion: These findings, combined with recent reports on the nutritional requirements of M. amazonicum, contribute to a deeper understanding of the digestive physiology of this species and offer valuable insights into its ability to utilize plant fibers as energy sources.

Here, we describe population and reproductive dynamics of four populations of Macrobrachium amazonicum in reservoirs during drought events. Additionally, we analyze possible phenotypic changes in this species promoted by fish predation. Two populations had a large-size phenotype (with large body proportions and morphotypes in males) while a small-size phenotype (with reduced sizes and no morphotypes) was found in the two other populations. Overall, females were larger than males and there were varying sex ratios among the four studied populations. All populations had bimodal or polymodal patterns in their monthly size-class frequency, suggesting a seasonal influence and a potentially great capacity of these populations to adapt to adverse environmental conditions. No major changes were found in the patterns of sex ratio, recruitment, frequency of (larger) male morphotypes and female ovarian development stages during drought events. Macrobrachium amazonicum is a resilient species and undergoes continuous reproduction. Females with immature ovaries were predominant in all populations, performing multiple spawns and exhibiting rapid ovarian development cycles. In males, the initial morphotype (TC - translucent claw) was predominant in populations with a social hierarchy. Males of dominant morphotypes (GC1 and GC2 - green claw 1 and 2) use more energy to carry out and maintain metabolic processes, which could probably one of the explanations why their number in populations are limited. We did not find any clear evidence that fish predation affected phenotypes, suggesting that phenotypic plasticity could be more related to intrinsic factors, which would have to be further investigated.

Introduction: Macrobrachium amazonicum is widely distributed in South America, occurring in the Orinoco, Amazon and Paraguay river basins, being used as an important source of protein for feeding riverside populations. This prawn is host to the crustacean ectoparasites Probopyrus pandalicola, Probopyrus floridensis and Probopyrus bithynis (Bopyridae) that infest the gill cavity of the species. Objective: To report the prevalence and abundance of ectopasites (P. pandalicola, P. floridensis and P. bithynis) and the condition factor in M. amazonicum from the Amazon River, Eastern Amazon. Methods: The prawns were collected from May 2017 to April 2018, with the artisanal trap matapi in the municipalities of Mazagão (state of Amapá) and Santarém (state of Pará), Brazil. Results: 216 prawns infected with ectoparasites were captured, 133 in the Mazagão region (53 P. pandalicola, 48 P. bithynis and 32 P. floridensis) and 83 in the Santarém region (45 P. pandalicola and 38 P. bithynis). In Mazagão, the highest prevalence values were recorded in May (1.98 %) for P. floridensis, July (2.18 %) for P. bithynis, and March (1.93 %) for P. pandalicola. In the Santarém region, the highest prevalence values were recorded in February, 3.47 for P. pandalicola and 2.89 for P. bithynis. Regarding the abundance of parasites, there was no difference between the species grouped between the regions (t = 0.32, p = 0.739). Parasitized prawns from Mazagão and Santarém presented condition factors below expectations, with an average of 0.85 ± 0.55 for Santarém and 0.88 ± 0.44 for Mazagão. Conclusions: During the study it was found that P. pandalicola, P. bithynis and P. floridensis were present in M. amazonicum throughout the year. Furthermore, there was an effect of parasitism on M. amazonicum in the study areas.

Los hidrocarburos aromáticos policíclicos (HAPs) son contaminantes tóxicos que generan riesgos para la salud humana y de los ecosistemas, debido a su persistencia en el ambiente; lo que ha incentivado el uso de herramientas como los biomarcadores obtenidos a partir de un bioindicador. No obstante, en regiones como Sudamérica con gran riqueza de especies acuáticas, y con países donde hay una alta demanda en la extracción de petróleo crudo, las investigaciones mediante el uso de biomarcadores han sido poco exploradas. Así mismo, se han identificado que la respuesta en especies de Caridea (Arthropoda: Malacostraca) en cuerpos de agua cercanos a los sitios contaminados puede proporcionar una advertencia temprana del efecto de los mismos e información para los programas de monitoreo ambiental. Con base en ello, se planteó como objetivo realizar una revisión sistemática referente a las especies de camarones como bioindicadores en estudios de contaminación por HAPs y los biomarcadores empleados en estas especies; y adicionalmente proponer una especie de Caridea para estudios de contaminación por HAPs en países de sur América. Como resultado se identificó que Macrobrachium fue el género con más estudios, empleando biomarcadores como CYP1A, actividad EROD, actividad GST, enzimas (SOD, CAT GPS, GSH y LPO), parámetros reproductivos (VTG), genotóxicos (ensayo cometa y de desenrollado de ADN), fisiológicos y morfológicos. Además, se propone a Macrobrachium amazonicum con potencial como bioindicador para la detección temprana de contaminantes dado su distribución y abundancia en países de Sur América como Colombia donde hay una alta demanda de petróleo.

The use of aquaponic systems has grown in recent years, but few of these systems have integrated the production of prawns and short-cycle vegetables. This study evaluated the potential for producing microgreens (beet, amaranth, arugula, and red cabbage) integrated with Amazon River prawns (Macrobrachium amazonicum) in an aquaponic system. Four seeding densities (5, 10, 15, or 20 seeds/cell) were assessed in two treatments: one using prawn wastewater and the other using plain dechlorinated water (control). Water quality, prawn growth performance, and microgreen productivity were monitored over 13 days, revealing optimal conditions for both prawns and microgreens in the aquaponic system. Amaranthus paniculatus yielded 374.00 g/m2 in prawn wastewater compared to 231.34 g/m2 in the control, while Beta vulgaris produced 1734.39 g/m2 in wastewater versus 1127.69 g/m2 in the control. Similarly, Brassica oleracea (2180.69 g/m2) and Eruca sativa (2109.46 g/m2) had higher yields in the prawn aquaponics system. These findings demonstrate that integrating prawn cultivation in aquaponic systems significantly enhances microgreen production compared to traditional methods. This integrated approach not only improves yields but also offers a more sustainable production model. Significant variation in productivity and growth metrics among species treatments underscores the viability and need for more systematic aquaponic procedures.

(Na+, K+)- ATPase kinetics in Macrobrachium pantanalense: highlighting intra- and interspecific variation within the Macrobrachium amazonicum complex