Amino acid compounds released by the giant freshwater prawn Macrobrachium rosenbergii during ecdysis: a factor attracting cannibalistic behaviour? / 浙江大学学报（英文版）（B辑：生物医学和生物技术）

Ecdysis is a common phenomenon that happens throughout the life phase of the giant freshwater prawn Macrobrachium rosenbergii. It is vital to better understand the correlation between cannibalism and biochemical compound that exists during the moulting process. The objective of the present study was to determine the amino acid profile released by M. rosenbergii during the ecdysis process that promotes cannibalism. To accomplish this, changes in amino acid levels (total amino acid (TAA) and free amino acid (FAA)) of tissue muscle, exoskeleton, and sample water of culture medium from the moulting (E-stage) and non-moulting (C-stage) prawns were analysed using high-performance liquid chromatography (HPLC). Comparison study revealed that among the TAA compounds, proline and sarcosine of tissues from moulting prawn were found at the highest levels. The level of FAA from water that contains moulting prawns (E-stage) was dominated by tryptophan and proline. Significant values obtained in the present study suggested that these amino acid compounds act as a chemical cue to promote cannibalism in M. rosenbergii during ecdysis. The knowledge of compositions and compounds that were released during the moulting process should be helpful for better understanding of the mechanism and chemical cues that play roles on triggering cannibalism, and also for future dietary manipulation to improve feeding efficiencies and feeding management, which indirectly impacts productivity and profitability.

Abundance and spatial-temporal distribution of Macrobrachium surinamicum Holthuis, 1948 (Palaemonidae) in the Amazon estuary, north of Brazil / Abundância e distribuição espaço-temporal de Macrobrachium surinamicum Holthuis, 1948 (Palaemonidae) em um estuário Amazônico, norte do Brasil

Abstract Macrobrachium surinamicum is a small shrimp that inhabits rivers of low salinity. It is mainly caught as bycatch in Amazon shrimp Macrobrachium amazonicum fisheries, which is widely exploited by artisanal fisheries for food and economic needs of the riverside population. This study aimed to characterize the spatial and temporal distribution of the freshwater shrimp M. surinamicum in the Guajará Bay and on Mosqueiro Island, correlating the abundance of this species with abiotic factors (temperature and salinity). Samples were taken from May 2006 to April 2007 in six locations: Mosqueiro Island (Furo das Marinhas and Porto do Pelé); Icoaraci district; Arapiranga Island, edge of the city of Belém; and Combu Island, using traps named 'matapis'. A total of 361 shrimps were caught. The abundance was higher in December and lower in July 2006. The biggest catch occurred on Arapiranga Island and the lowest on Mosqueiro Island. The abundance differed significantly in December 2006 and no variable studied had significant influence on M. surinamicum abundance. In Guajará Bay, particularly the more sheltered places, as Arapiranga and Combu islands, favor the development of M. surinamicum, indicating that this species has preference for less disturbed areas.

Resumo Macrobrachium surinamicum é um camarão de pequeno porte que habita a foz de rios e águas de baixa salinidade. Sua captura na Amazônia ocorre principalmente como fauna associada à pesca do camarão-da-Amazônia Macrobrachium amazonicum que é largamente explorado pela pesca artesanal atendendo as necessidades alimentícias e econômicas da comunidade ribeirinha. O presente estudo teve como objetivo caracterizar a distribuição espaço-temporal do camarão dulcícola M. surinamicum na Baía do Guajará e Ilha de Mosqueiro, correlacionando a abundância desta espécie com fatores abióticos (temperatura e salinidade). Os exemplares foram capturados no período de maio/06 a abril/07 em seis locais: Ilha de Mosqueiro (Furo das Marinhas e Porto do Pelé), Distrito de Icoaraci, Ilha do Arapiranga, orla de Belém e Ilha do Combu com armadilhas (matapis). Um total de 361 camarões foi capturado, sendo a maior abundância em dezembro e a menor em julho de 2006. A maior captura foi na Ilha de Arapiranga e a menor na Ilha de Mosqueiro. A abundância diferiu significativamente em dezembro/06 e nenhuma variável estudada teve influência significativa na abundância de M. surinamicum. A Baía do Guajará, especialmente os locais mais abrigados como a Ilha de Arapiranga e do Combu, propiciam o desenvolvimento de M. surinamicum, o que indica que esta espécie tenha preferência para áreas menos antropizadas.

Reproductive biology of Macrobrachium surinamicum (Decapoda: Palaemonidae) in the Amazon River mouth / Biologia reprodutiva do camarão Macrobrachium surinamicum (Decapoda: Palaemonidae) na foz do rio Amazonas

Macrobrachium surinamicum is an indigenous prawn distributed from the lower Amazon and Tocantins river basins to Venezuela in the Orinoco Delta region. It is common bycatch fauna of Macrobrachium amazonicum artisan fishing in the states of Pará and Amapá. The aim of this study was to investigate aspects on reproductive biology (reproductive period, size of sexual maturity population, fecundity, reproductive output and recruitment) of M. surinamicum from four important areas to artisanal prawn fishing located at the Amazon River mouth (Amapá and Pará). The specimens were captured using 20 handcrafted traps called "matapi". A number of 675 prawns were captured, 258 males, 409 females and eight juveniles, resulting in 1:1.6 (Male: Female) sex ratio. The reproductive peak period occurred from March to July, coinciding with the higher rainfall period. The juvenile prawn occurred only in May and July. Total length of egg-bearing females ranged from 12.12 to 38.30 mm, with mean female length at first maturity (L50) of 23.7 mm. Fecundity increased with prawn size and varied between 174 and 1780 eggs per female. Mean egg volume increased gradually from 0.031 (Stage I) to 0.060 mm³ (Stage III) during embryogenesis. Macrobrachium surinamicum depends on brackish water to complete the larval development. Irrespective of female size, reproductive output of M. surinamicum varied between 4.3 % and 35.5 % of their body weight for egg production. The knowledge of the reproductive biology reported in the present study is an important tool to define strategies to preserve M. surinamicum in Amazon River mouth.

Macrobrachium surinamicum é uma espécie nativa de camarão de água doce distribuída do Brasil, nas bacias do rio Amazonas e Tocantins até a Venezuela na região do Delta do Orinoco. Este é fauna acompanhante comum da pesca artesanal de Macrobrachium amazonicum nos estados do Pará e Amapá. O objetivo deste trabalho foi abordar aspectos gerais da biologia reprodutiva (período reprodutivo, tamanho de primeira maturação, fecundidade, investimento reprodutivo e recrutamento) de M. surinamicum de quatro importantes áreas de pesca artesanal de camarão localizada na foz do rio Amazonas (Amapá e Pará). Os exemplares foram capturados usando 20 armadilhas artesanais, conhecidas localmente como matapi. Um total de 675 camarões foi capturado, 258 machos, 409 fêmeas e oito juvenis, resultando uma razão sexual geral de 1: 1,6 (macho:fêmea). Os picos reprodutivos ocorreram de março a julho, coincidindo com o período mais chuvoso. Os jovens foram observados em maio e julho. O comprimento total das fêmeas ovígeras variou de 12,12 a 38,30 mm, com o comprimento de primeira maturação (L50) estimado em 23,7 mm. A fecundidade aumentou com o tamanho das fêmeas, variando entre 174 e 1780 ovos por espécime. Volume médio dos ovos aumentou gradualmente durante a embriogênese saindo de 0,031 (Estágio I) para 0,060mm³ (Estágio III). Macrobrachium surinamicum dependem de água salobra para completar seu desenvolvimento larval. Independentemente do tamanho da fêmea, o investimento reprodutivo de M. surinamicumvariou entre 4,3 % e 35,5% do seu peso corporal para a produção de ovos. O conhecimento da biologia reprodutiva relatada no presente estudo é uma ferramenta importante para ajudar a definir estratégias para preservar M. surinamicum na foz do Rio Amazonas.

Effect of salinity on the metabolism and osmoregulation of selected ontogenetic stages of an amazon population of Macrobrachium amazonicum shrimp (Decapoda, Palaemonidae) / Efeito da salinidade sobre o metabolismo e a osmorregulação de estágios ontogenéticos selecionados de uma população amazônica do camarão Macrobrachium amazonicum (Decapoda, Palaemonidade)

Probably as a function of their wide geographical distribution, the different population of Macrobrachium amazonicum shrimp may present distinct physiological, biochemical, reproductive, behavioral, and ecological patterns. These differences are so accentuated that the existence of allopatric speciation has been suggested, although initial studies indicate that the genetic variability of populations happen at an intraspecific level. Among the biological responses described for M. amazonicum populations, those regarding osmoregulation and metabolism play a key role for being related to the occupation of diverse habitats. To this effect, we investigated osmoregulation through the role of free amino acids in cell volume control and metabolism, through oxygen consumption in larvae (zoeae I, II, V and IX) and/or post-larvae of a M. amazonicum population from Amazon, kept in aquaculture fish hatcheries in the state of São Paulo. The results add information regarding the existence of distinct physiological responses among M. amazonicum populations and suggest that possible adjustments to metabolism and to the use of free amino acids as osmolytes of the regulation of the larvae and post-larvae cell volume depend on the appearance of structures responsible for hemolymph osmoregulation like, for example, the gills. In this respect, we verified that zoeae I do not alter their metabolism due to the exposition to fresh or brackish water, but they reduce intracellular concentration of free amino acids when exposed to fresh water, what may suggest the inexistence or inefficient performance of the structures responsible for volume regulation and hemolymph composition. On the other hand, in zoeae II and V exposed to fresh and brackish water, metabolism alterations were not followed by changes in free amino acids concentration. Thus it is possible, as the structures responsible for osmoregulation and ionic regulation become functional, that the role of free amino acids gets diminished and oxygen consumption elevated, probably due to greater energy expenditure with the active transportation of salts through epithelial membranes. Osmotic challenges also seem to alter throughout development, given that in zoeae II oxygen consumption is elevated on brackish water of 18, but in zoeae V it happens in fresh water. After M. amazonicum metamorphosis, free amino acids begin to play an important role as intracellular osmolytes, because we verified an increase of up to 40% in post-larvae exposed to brackish water of 18. The main free amino acids involved in cell volume regulation of ontogenetic stages evaluated were the non essential ones: glutamic acid, glycine, alanine, arginine, and proline. Interestingly, larvae from estuarine population studied here survived until the zoeae V stage in fresh water, but in some populations far from the sea, zoeae die right after eclosion in fresh water or they do not reach zoeae III stage. In addition, given that in favorable conditions caridean shrimp larvae shorten their development, we may infer that the cultivation environment, in which larvae developed in the present work, was appropriate, because almost all zoeae VIII kept on brackish water underwent metamorphosis directly to post-larvae and did not go through zoeae IX stage.

Provavelmente como função da sua ampla distribuição geográfica, as diferentes populações do camarão Macrobrachium amazonicum podem apresentar distintos padrões fisiológicos, bioquímicos, reprodutivos, comportamentais e ecológicos. Essas diferenças são tão acentuadas que tem sido sugerido a existência de especiação alopátrica embora estudos iniciais indiquem que a variabilidade genética das populações ocorre ao nível intraespecífico. Dentre as respostas biológicas descritas para as populações de M. amazonicum, aquelas relacionadas à osmorregulação e metabolismo têm papel central por estarem relacionadas à ocupação dos diversos habitats. Nesse sentido, investigou-se a osmorregulação, por meio do papel dos aminoácidos livres no controle do volume celular e o metabolismo, por meio do consumo de oxigênio, em larvas (zoeas I, II, V e IX) e/ou pós-larvas de uma população de M. amazonicum oriunda da Amazônia e mantida em viveiros de aquicultura no estado de São Paulo. Os resultados adicionam informações a respeito da existência de respostas fisiológicas distintas entre as populações de M. amazonicum e sugerem que possíveis ajustes no metabolismo e no uso de aminoácidos livres como osmólitos da regulação do volume celular das larvas e pós-larvas dependem do surgimento de estruturas responsáveis pela osmorregulação da hemolinfa como, por exemplo, as brânquias. Nesse sentido, verificou-se que as zoeas I não alteram seu metabolismo em função da exposição à água doce ou salobra, mas reduzem a concentração intracelular de aminoácidos livres quando expostas à água doce, o que pode sugerir a inexistência ou um desempenho ineficiente das estruturas responsáveis pela regulação do volume e composição da hemolinfa. Por outro lado, nas zoeas II e V expostas à água doce ou salobra alterações no metabolismo não foram acompanhadas por mudanças na concentração dos aminoácidos livres. Assim é possível que à medida que estruturas responsáveis pela osmo e ionorregulação tornam-se funcionais, o papel dos aminoácidos livres se torne reduzido e o consumo de oxigênio elevado, provavelmente em função do maior gasto energético com o transporte ativo de sais através das membranas epiteliais. Os desafios osmóticos também parecem se alterar ao longo do desenvolvimento visto que em zoeas II o consumo de oxigênio é elevado em água salobra de 18 mas em zoeas V essa resposta ocorre em água doce. Após a metamorfose de M. amazonicum, os aminoácidos livres passam a ter papel importante como osmólitos intracelulares, pois se verificou um aumento de até 40% nas pós-larvas expostas à água salobra de 18. Os principais aminoácidos livres envolvidos na regulação do volume celular dos estágios ontogenéticos avaliados foram os não essenciais ácido glutâmico, glicina, alanina, arginina e prolina. Interessantemente, as larvas da população estuarina aqui estudada sobrevivem até o estágio de zoea V em água doce mas em algumas populações distantes do mar as zoeas morrem logo após a eclosão em água doce ou não chegam ao estágio de zoea III. Adicionalmente, visto que em condições favoráveis as larvas de camarões carídeos abreviam o seu desenvolvimento pode ser inferido que o meio de cultivo em que as larvas se desenvolveram no presente trabalho foi adequado, pois quase todas as zoeas VIII mantidas em água salobra sofreram diretamente a metamorfose para pós-larvas e não passaram pelo estágio de zoeas IX.

The effect of astaxanthin on resistance of juvenile prawns Macrobrachium nipponense (Decapoda: Palaemonidae) to physical and chemical stress / Efecto de la astaxantina en la resistencia al estrés físico y químico de los langostinos jóvenes de Macrobrachium nipponense (Decapoda: Palaemonidae)

In recent years, the use of new scientific techniques has effectively improved aquaculture production processes. Astaxanthin has various properties in aquacultureand its antioxidant benefits have been closely related to stress resistance; besides, it is an essential factor for growth in many crustaceans and fish. The objective of this study was to evaluate the resistance of prawn (Macrobrachium nipponense) fed diets containing different amounts of astaxanthin (AX) to the shock and stress of differentphysicochemical environments. A 70-day trial was conducted to evaluate the effect of supplementation of a source of astaxanthin (Carophyll Pink, 10% astaxanthin, w/w, Hoffman-La Roche, Switzerland) at various levels in the diet of M. nipponense juveniles. Four dry diets were prepared: AX0 without astaxanthin, AX50 with 50mg/kg, AX100 with 100mg/kg, and AX150 with 150mg/kg astaxanthin. The feeding trial was conducted in a recirculation water system consisting of 12 fiberglass tanks (1 000L) used for holding prawns. Three replicate aquaria were initially stocked with 36org/m² per tank. During the trial, prawns were maintained on a 12:12-h light:dark photoperiod with an ordinary incandescent lamp, and the water quality parameters were maintained as follows: water temperature, 25-26°C; salinity, 1g/L; pH, 8.5-8.8; dissolved oxygen, 6.0-6.5mg/L; and ammonia-nitrogen, 0.05mg/L. Incorporation of AX, production output, and physiological condition were recorded after 10 weeks of feeding. At the end of the growing period, the prawns were exposed to thermal shock (0°C), ammonia (0.75mg/L), and reduced oxygen (0.5mg/L). The time to lethargyand the time to complete death of the prawns were recorded. The results showed that control prawns had the shortest time to lethargy and death compared with prawns subjected to the other treatments. The results of this study have shown that the amount of muscle tissue and gill carotenoids in prawn fed with an AX150 diet showed greater reduction than those exposed to other treatments. It is possible that higher levels of astaxanthin in the body under oxygen reduction stress can be beneficial forprawns. These results suggest that male prawns showed lethargy earlier than females, and the percentage of carotenoid reduction in muscle and gill tissues was higher inmales. Rev. Biol. Trop. 62 (4): 1331-1341. Epub 2014 December 01.

En años recientes, la utilización de nuevas técnicas científicas ha tenido un efecto importante en mejorar los procesos de producción en acuicultura. La astaxantina tiene varias propiedades en la acuicultura y sus propiedades antioxidantes se encuentran estrechamente relacionadas con la resistencia al estrés. La astaxantina en muchos crustáceos y peces es un factor esencial para el crecimiento. El objetivo de este estudio fue evaluar la resistencia del langostino (Macrobrachium nipponense) alimentado con dietas conteniendo diferentes cantidades de astaxantina (AX), bajo diferentes condiciones de estrés ambiental. Un ensayo de 70 días fue llevado a cabo para evaluar el efecto de la suplementación de fuentes de astaxantina (Carophyll Pink, 10 % astaxanthin) en varios niveles en la dieta de jóvenes de M. nipponense. Cuatro dietas fueron preparadas: AX0 sin astaxantina, AX50 con 50mg/kg, AX100 con 100mg/kg y AX150 con 150mg/kg de astaxantina. Los ensayos de alimentación fueron conducidos en un sistema de recirculación de agua consistente en 12 estanques de fibra de vidrio (1 000L). Tres replicas fueron sembradas con 36org/m2 por tanque. Durante el experimento los langostinos fueron mantenidos con un fotoperiodo de 12:12 luz:oscuridad con lámparas incandescentes y los parámetros de la calidad del agua fueron mantenidos a 25-26°C la temperatura, 1 g/L la salinidad, 8.5-8.8 el pH, 6.0-6.5 mg/L el oxígeno y 0.05mg/L el nitrógeno amoniacal. La incorporación de la astaxantina, producción y condiciones fisicoquímicas fueron registradas después de 10 semanas de alimentación. Al final del periodo de crecimiento, los langostinos fueron expuestos a un shock térmico (0°C), amonio (0.75mg/L) y reducción de oxígeno 0.5 mg/L. El tiempo de letargia y el tiempo de muerte fueron registrados. Se encontró que la dieta con la mayor concentración de astaxantina (150mg/kg) presentó el mayor tiempo de letargia y la mayor concentración en branquias y músculo en el langostino M. nipponense.

Treatment efficiency of effluent prawn culture by wetland with floating aquatic macrophytes arranged in series / Eficiência de wetland com macrófitas aquáticas flutuantes dispostas em serie para o tratamento do efluente do cultivo de camarão

The efficiency of a series of wetland colonized with Eichhornia crassipes and Salvinia molesta to treat the effluent of a giant river prawn (Macrobrachium rosenbergii) broodstock pond was evaluated in this study. The experimental design was completely randomized and was performed in 9 rectangular tanks (1.6 m3) with three treatments (constructed wetlands) and three replicates. The treatment types included: a wetland colonized with E. crassipes and S. molesta (EcSm) arranged sequentially, a wetland with E. crassipes only (Ec) and a wetland with S. molesta only (Sm). The means of suspended particulate material (SPM), total inorganic nitrogen (TIN), total Kjeldahl nitrogen (TKN), P-orthophosphate (PO4-P) and total phosphorus (TP) of the treated effluents were compared using ANOVA followed by Tukey's test (P<0.05). The effluent treated in Ec and EcSm wetlands exhibited lower SPM concentrations. The Ec wetland reduced TIN, TKN, PO4-P and TP by 46.0, 43.7, 44.4 and 43.6%, respectively. In the EcSm wetland, the reduction of TIN (23.0%), TKN (33.7%) and PO4-P (26.7%) was similar to the Sm wetland (19.8% TIN, 30.9% TKN and 23.8% PO4-P). The Ec wetland was more efficient in treating pond effluent due likely to the higher root surface of E. crassipes, which forms an extensive area favorable to retention and adsorption of debris and absorption of nutrients.

Neste estudo foi avaliada a eficiência de uma wetland povoada com Eichhornia crassipes e Salvinia molesta para o tratamento do efluente de um viveiro de manutenção de reprodutores do camarão-da-malásia (Macrobrachium rosenbergii). Um experimento totalmente casualizado foi realizado em 9 tanques retangulares (1,6 m3) com 3 tratamentos (wetlands construídas) e 3 repetições. Os tratamentos foram: wetland povoada com E. crassipes e S. molesta (EcSm) dispostas nesta sequência, wetland somente com E. crassipes (Ec) e wetland somente com S. molesta (Sm). Os valores de material particulado em suspensão (MPS), nitrogênio inorgânico total (NIT), nitrogênio Kjeldahl total (NKT), P-ortofosfato (P-PO4) e fósforo total (PT) dos efluentes tratados foram comparados pela ANOVA seguida do teste de Tukey (P<0,05). A wetland Ec reduziu a concentração de NIT, NKT, P-PO4 e PT em 46,0%, 43,7%, 44,4% e 43,6%. Na wetland EcSm a redução de NIT (23,0%), NKT (33,7%) e P-PO4 (26,7%) foi semelhante à observada na wetland Sm (19,8% para NIT, 30,9% para NKT e 23,8% para P-PO4). A wetland povoada com E. crassipes é mais eficiente no tratamento do efluente do viveiro, provavelmente devido a maior superfície radicular da macrófita que permite a formação de uma extensa área propícia à retenção e adsorção dos detritos e à absorção dos nutrientes.

Ocurrence of male morphotypes of Macrobrachium amazonicum (Caridea, Palaemonidae) in a population with an entirely freshwater life cycle / Ocorrência de morfotipos em machos de Macrobrachium amazonicum (Caridea, Palaemonidae) em uma população com ciclo de vida completamente dulcícola

This study records, for the first time, the occurrence of all four male morphotypes in a population of Macrobrachium amazonicum from a continental environment, with an entirely freshwater life cycle. The specimens studied came from the Tietê River, state of São Paulo, Brazil, and were collected in a lotic environment downstream from Ibitinga Dam. This population was compared with other continental populations, including a population from the dam itself, collected in a previous study. Four samples of 30 minutes were taken monthly, using a trap, from January to April 2011. Each male specimen was measured with respect to seven body dimensions as follows: carapace length (CL), right cheliped length (RCL), dactyl length (DCL), propodus length (PPL), carpus length (CRL), merus length (ML) and ischium length (IL). The relative growth was analyzed based on the change in growth patterns of certain body parts in relation to the independent variable CL. The four male morphotypes proposed for the species were found using morphological and morphometric analyses. Different biological characteristics were found between the populations studied. The male population of the lake of Ibitinga and from Pantanal presented mean sizes and number of morphotypes lower than the population studied here. These differences seem to be closely related to ecological characteristics of the environments inhabited by these populations. Our results supported the hypothesis that coastal and continental populations of M. amazonicum belong to the same species.

Este estudo registra, pela primeira vez, a ocorrência dos quatro morfotipos de Macrobrachium amazonicum em uma população continental com ciclo de vida totalmente dulcícola. Os camarões são provenientes do Rio Tietê, estado de São Paulo, Brasil, e foram coletados em um ambiente lótico abaixo da Barragem de Ibitinga. Essa população foi comparada com outras populações provenientes de ambientes continentais, incluindo a de um estudo anterior na represa da barragem de Ibitinga. Quatro amostras de 30 minutos foram realizadas mensalmente, utilizando armadilhas, de janeiro a abril de 2011. Cada indivíduo macho foi mensurado em relação a sete dimensões corporais, sendo elas: comprimento da carapaça (CL), comprimento total do quelípodo direito (RCL), comprimento do dáctilo (DCL), comprimento do própodo (PPL), comprimento do carpo (CRL), comprimento do mero (ML) e comprimento do ísquio (IL). O crescimento relativo foi analisado de acordo com as mudanças nas taxas de crescimento de determinadas partes do corpo em relação à variável independente CL. Os quatro morfotipos descritos para a espécie foram encontrados, utilizando análises morfológicas e morfométricas. Diferentes características biológicas foram encontradas entre a população estudada e as demais, incluindo a proveniente do reservatório. A população de machos da represa de Ibitinga e do Pantanal apresentaram tamanhos médios e número de morfotipos inferiores aos da população estudada aqui. Essas diferenças parecem estar intimamente relacionadas às características ecológicas dos ambientes onde estas populações estão inseridas. A hipótese de que populações costeiras e continentais de M. amazonicum pertençam à mesma espécie é suportada por nossos resultados.

Reproductive aspects of Macrobrachium amazonicum (Decapoda: Palaemonidae) in the State of Amapá, Amazon River mouth / Aspectos reprodutivos do camarão Macrobrachium amazonicum (Decapoda: Palaemonidae) no estado do Amapá, foz do rio Amazonas

Macrobrachium amazonicum is an indigenous prawn vastly distributed in basins of South America, widely exploited by artisanal fisheries in northern and northeastern Brazil and, with great potential for aquaculture. This study aimed to investigate general aspects of population structure and reproductive characteristics (size at first maturity, fecundity and reproductive output) of M. amazonicum from two important areas to artisanal prawn fishing located at the mouth of the Amazon River, State of Amapá. The specimens were captured using 20 handcrafted traps called "matapi". A number of 5,179 prawns were captured, 2,975 females and 2,195 males resulting in 1.35:1 female to male ratio. Santana Island and Mazagão Velho showed females predominated in the population. A reproductive peak period was observed from January to April/2009 and in December/2010, coinciding with the period of higher rainfall. The recruitment peak occurred in June and July/2009. Egg-bearing females ranged in size (carapace length) from 11.10 to 29.6 mm. Fecundity increased with female size and reached up to 7,417 eggs. This amount of eggs is considered low if compared with other Macrobrachium estuarine species. Mean egg volume increased gradually from 0.121 to 0.24 mm³ during embryogenesis, representing 68.5% of overall increase from Stage I to Stage III. Eggs of M. amazonicum are small; this is typical for Macrobrachium species, which depends on brackish water to complete the larval development. Irrespective of female size, reproductive output of M. amazonicum varied between 4.8 and 21.85% of their body weight into eggs production.

Macrobrachium amazonicum é uma espécie nativa vastamente distribuída nas bacias da America do Sul, sendo largamente explorada por pescadores artesanais no Norte e Nordeste do Brasil e com grande potencial para aquicultura. O objetivo deste trabalho foi abordar aspectos gerais da estrutura populacional e biologia reprodutiva (tamanho de primeira maturação, fecundidade e investimento reprodutivo) de M. amazonicum de duas importantes áreas de pesca artesanal de camarão localizada na foz do rio Amazonas, no Estado do Amapá. Os exemplares foram capturados usando 20 armadilhas artesanais, conhecidas localmente como matapi. Um total de 5.179 camarões foi capturado, dos quais 2.975 eram fêmeas e 2.195 eram machos, dando uma razão sexual geral de 1,35: 1 em favor das fêmeas. As proporções sexuais nas áreas de Ilha de Santana e Mazagão mostraram fêmeas predominando na população. Os picos reprodutivos nas duas áreas ocorreram de Janeiro a Abril/2009 e em Dezembro/2010, coincidindo com o período mais chuvoso. Os picos de recrutamento foram observados em junho e julho de 2009. O tamanho das fêmeas ovígeras variou de 11,10 mm a 29,6 mm de comprimento de carapaça. A fecundidade aumentou com o tamanho das fêmeas, chegando até 7.417 ovos, podendo ser considerada baixa comparada a outras espécies estuarinas de Macrobrachium. Volume médio dos ovos aumentou gradualmente durante a embriogênese saindo de 0,112 para 0,220 mm³, representando um aumento global de 68,5% do I ao III estágio embrionário. Os ovos de M. amazonicum podem ser considerados pequenos, típicos de espécies de Macrobrachium que dependem de água salgada para completar seu desenvolvimento larval. Independente do tamanho da fêmea, o investimento reprodutivo de M. amazonicum variou entre 4,8 e 21,85% do seu peso corporal para a produção de ovos.

Reproductive and morphometric traits of Macrobrachium amazonicum (Decapoda: Palaemonidae) from the Pantanal, Brazil, suggests initial speciation

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 at least incipient vicariant speciation.

El camarón palaemónido Macrobrachium amazonicum muestra una distribución geográfica inusualmente grande (aprox. 4 000km de diámetro), vive en las zonas costeras, estuarios y hábitats interiores límnicos del alto Amazonas, Orinoco y las cuencas de La Plata. Esto plantea dudas sobre sí poblaciones alopátricas y ecológicamente diversas pertenecen a la misma especie. Mientras que los camarones de estuarios y de hábitats Amazónicos se han estudiado con gran detalle, se sabe muy poco acerca de las poblaciones holo-limnéticas del interior. En el presente estudio, los rasgos biológicos relacionados con el crecimiento (tamaño máximo del cuerpo, peso fresco, relaciones morfométricas) y la reproducción (proporción de sexos; ocurrencia de morfotipos masculinos; tamaño mínimo sexable; tamaño mínimo de las hembras ovígeras; fecundidad; tamaño del huevo), fueron estudiados en M. amazonicum recolectados en un estanque de cultivo y dos hábitats naturales de agua dulce (Río Miranda; Baiazinha Lagoa) en el Pantanal de Mato Grosso do Sul, Brasil. En total, 2 270 camarones fueron examinados (603 machos, 1 667 hembras, 157 de estas ovígeras). La proporción de sexos (machos:hembras) fue en todos los sitios de muestreo fuertemente sesgada por hembras, desde 0.2 hasta 0.6. El tamaño corporal máximo fue mayor en los hábitats naturales comparado con el estanque de cultivo, sugeriendo un crecimiento reducido o un lapso de vida más corto en condiciones artificiales de crianza masiva. La fecundidad máxima observada en nuestro material fue 676 huevos, alcanzado por la hembra de mayor tamaño (largo total, LT=65mm). Una diferencia significativa entre los parámetros de pendiente de regresiones lineales que describen la fecundidad, comparando el número de huevos puestos o de larvas liberadas, en relación con el peso de la hembra, indican pérdida de huevos. Esto puede ser debido a un aumento de 2.4 veces en el volumen del huevo que ocurre durante el desarrollo embrionario, mientras que el espacio disponible bajo el abdomen sigue siendo limitado. Relaciones de tamaño-peso diferían significativamente entre machos y hembras, lo que indica diferencias morfométricas sexoespecíficas. Los machos parecen tener una forma de cuerpo más delgado que las hembras, alcanzando por lo tanto el peso más bajo en la igualdad de LT. Cuando los rasgos reproductivos y morfométricos son comparados con datos de la literatura de poblaciones estuarinas y poblaciones del interior que viven en el Amazonas y en los llanos del Orinoco, los camarones del Pantanal muestran peculiaridades diferentes: (1) el tamaño máximo del cuerpo es mucho más pequeño, lo que sugiere menor longevidad; (2) las hembras son más grandes que los machos; (3) diferentes morfotipos masculinos están ausentes; (4) el tamaño mínimo sexable y (5) el tamaño mínimo de hembras ovígeras son más pequeños. Estas características sugieren un cambio heterocrónico (pre-desplazamiento) de la maduración sexual y la selección-r. En resumen, nuestros datos muestran diferencias biológicamente relevantes en los rasgos de la historia de vida de los camarones del Pantanal comparados con M. amazonicum en otras regiones. Todas estas diferencias persisten también en cultivos a largo plazo mantenidos bajo condiciones constantes. En conjunto, nuestros datos apoyan la hipótesis que M. amazonicum en la desembocadura de la cuenca Paraná-Paraguay ha divergido filogenéticamente de poblaciones alopátricas que están hidrológicamente separadas por cuencas continentales, lo que implica al menos una incipiente especiación vicariante.

Trophic ecology of the freshwater prawn, Pseudopalaemon bouvieri (Decapoda: Palaemonidae) in Northeastern Argentina: with remarks on population structure

Freshwater decapod crustaceans are important components of food webs in these environments, but little is known about the diet of species that live in tropical waters. We studied the feeding ecology of the prawn Pseudopalaemon bouvieri and its population structure in two different areas with six lagoons, with a different composition and abundance of aquatic macrophytes. At each site of macrophytes banks, 18 prawns sample was collected with a hand net (1mm mesh size) from 1m². In the laboratory, prawns cephalothorax length was measured, sex determined, and a total of 208 stomachs were examined for food items. Our results showed that the population abundance varied between 10 ind/m² and 1 411 ind/m². The cephalothorax length ranged between 6mm and 21mm, and the male:female ratio varied between 0.3 and 1.0, with a higher proportion of ovigerous females (21%) in area one than area two. P. bouvieri is omnivorous, and its diet was principally based on algae, plant remains, Protozoa, Rotifera, Oligochaeta, Crustacea, Insecta, detritus and other items. The analysis of the stomach content did not reveal any significant difference in the diet between juveniles and adults, and males and females of both areas consumed a similar diet (Kruskal-Wallis test p=0.8273). We concluded that the dietary items consumed by prawns and the niche breadth were similar between the two areas, although the proportion of items consumed varied between lagoons of both areas. The density of P. bouvieri was different between areas, but the size of cephalothorax (CL) was similar.

Los crustáceos decápodos de agua dulce son un componente importante de la cadena trófica, pero poco se sabe sobre la dieta de las especies que viven en aguas tropicales. Nosotros estudiamos la ecología alimentaria del camarón Pseudopalaemon bouvieri y la estructura de su población en dos áreas diferentes con seis lagunas, con una diferente composición y abundancia de macrófitas acuáticas. En cada sitio poblado con macrófitas, se tomaron 18 muestras con una red manual (1mm de tamaño de malla) de 1m². En laboratorio, se midió la longitud de cefalotórax de los camarones y se determinó el sexo. Asimismo, fueron examinados un total de 208 estómagos para determinar su alimentación. Nuestros resultados mostraron que la abundancia de la población varió entre 10 ind/m² y 1 411 ind/ m². La longitud de cefalotórax osciló entre 6 y 21mm, y la razón macho:hembra varió entre 0.3 y 1.0, con una mayor proporción de hembras ovígeras (21%) en el área 1 que en el área 2. P. bouvieri es omnívoro y su alimentación se basa principalmente en algas, restos de plantas, protozoos, rotíferos, Oligochaeta, crustáceos, Insecta, detrito y otros ítems. El análisis del contenido estomacal no reveló ninguna diferencia significativa en la dieta entre juveniles y adultos, y los machos y hembras de ambas áreas consumieron una dieta similar (Kruskal-Wallis, p=0.8273). Nosotros concluimos que los ítems alimentarios consumidos por los camarones y la amplitud de nicho fueron similares entre las dos áreas, aunque la proporción de ítems consumidos varió entre lagunas de ambas áreas. La densidad de P. bouvieri fue diferente entre áreas, pero el tamaño del cefalotórax (CL) fue similar.

Occurrence of the Indo-Pacific freshwater prawn Macrobrachium equidens Dana 1852 (Decapoda, Palaemonidae) on the coast of Brazilian Amazonia, with notes on its reproductive biology

The freshwater prawn Macrobrachium equidens, which is native species of the Indo-Pacific Region, was recorded for the first time on the Amazon coast of Brazil. This species was found to inhabit the same environment as two native Macrobrachium species, M. amazonicum and M. acanthurus, and is morphologically very similar to the latter. The identification of the species was confirmed by the genetic analysis of sequences of the mitochondrial Cytochrome Oxidase (COI) gene. A detailed description of the morphological features and reproductive biology of M. equidens in this new environment is presented.

O camarão de água doce Macrobrachium equidens, nativo da região do Indo-Pacífico, foi registrada pela primeira vez na costa da Amazônia Brasileira. Esta espécie foi encontrada habitando o mesmo ambiente que duas espécies nativas do gênero Macrobrachium: M. amazonicum e M. acanthurus, e é morfologicamente muito similar à última. A identificação dessa espécie foi confirmada pela análise da seqüência genética do gene mitocondrial Citocromo Oxidase (COI). Uma descrição detalhada das características morfológicas e biologia reprodutiva de M. equidens neste novo ambiente é apresentada.

Histoarchitectural features of the hepatopancreas of the Amazon River prawn Macrobrachium amazonicum / Histoarquitectura del hepatopáncreas del camarón de la Amazonia Macrobrachium amazonicum

In decapod crustaceans, the digestive gland is concerned with the digestion, absorption of nutrients, the storage of reserves and excretion. The metabolism and the histological and histochemical changes of the hepatopancreas are observed in response to physiological demands as moult, reproduction, digestive process. Thus the hepatopancreas structure should be recognized to provide important morphological information to future studies involving the nutrition requirements of freshwater prawn culture. In this study, second-generation Macrobrachium amazonicum produced from wild broodstock collected in the state of Para in Brazil were used. Thirty adult male and female M. amazonicum were selected and randomly transferred to five experimental units for macroscopic and microscopic studies. The hepatopancreas of M. amazonicum is a large, yellowish-brown, compact organ, which occupies much of the cephalothoracic cavity. It has right and left halves that are enclosed together in a laminar connective tissue capsule, and at the same time they are separated by an interstitial connective tissue. The two halves are thereby called the right and left hepatopancreatic lobes. The principal tubule gives rise to four secondary tubules at each hepatopancreatic lobe. The morphological and functional unit consists of a blind-ended hepatopancreatic tubule, considered in the present study as the hepatopancreatic lobule. Each hepatopancreatic tubule can be subdivided into distal, medial and proximal zones. The hepatopancreatic tubule is lined by a pseudostratified epithelium that consists of five different cell types, which include the E-cell (embryonic), F-cell (fibrillar), B-cell (blister-like), R-cell (resorptive) and M-cell (midgut or basal). It is important to emphasize that the function of each cell type in the hepatopancreas during the digestive cycle is not yet established for decapods.

La glándula digestiva en los crustáceos decápodos asume las funciones de digestión, absorción de nutrientes, almacenamiento de las reservas energéticas y excreción de metabolitos. El metabolismo y las alteraciones histológicas e histoquímicas son observados como respuesta a necesidades fisiológicas, tales como: muda, reproducción y procesos digestivos. Por lo tanto, se requiere conocer la estructura histológica del hepatopancreas con el fin de reunir información morfológica para futuros estudios que consideren las necesidades nutricionales para el cultivo de los camarones de agua dulce. Fueran utilizados 30 animales, machos y hembras de Macrobrachium amazonicum, producidos a partir de reproductores colectados en el Estado de Para, Brasil. Las observaciones macro y microscópicas permitieron concluir que el hepatopancreas del M. amazonicum es un órgano grande y compacto de color amarillo tendiendo a marrón, que ocupa la mayor parte de la cavidad céfalo-torácica. El órgano presenta dos mitades, derecha y izquierda, las cuales están envueltas por una cápsula de tejido conjuntivo, y al mismo tiempo, separadas por tejido conectivo intersticial. Las dos mitades del órgano son identificadas como lobos derecho e izquierdo. Cada lobo presenta un túbulo principal que origina cuatro túbulos secundarios. Por lo tanto, la unidad morfofuncional del hepatopancreas consiste en un túbulo hepatopancreático de fondo ciego, considerado en esta investigación como lóbulo hepatopancreático. Cada lóbulo hepatopancreático puede ser dividido en 3 regiones: distal, media y proximal, y en su totalidad, se observa revestido por epitelio seudo estratificado que reúne cinco tipos celulares: célula E (embrionaria), célula F (fibrilar), célula B (globosa), célula R (reabsortiva) y célula M (basal). Es importante enfatizar que la función de cada tipo celular del hepatopancreas no está todavía aclarada para los decápodos.

Reproductive cycle of Macrobrachium amazonicum females (Crustacea, Palaemonidae)

Macrobrachium amazonicum is considered a favorite Brazilian species of freshwater prawn for cultivation as a result of its quick development and because it is easy to maintain in captivity. The aim of this work is to describe the sexual cycle stages and determine maturation age of the female M. amazonicum, which was collected monthly from June, 2002 to May, 2003 in the Jaguaribe River, Itaiçaba, Ceará. A monthly sample of water was also collected to determine the following parameters: temperature, dissolved oxygen, pH and salinity. A monthly sample of females was selected among the individuals caught, to determine the total weight (W T), carapace length (L C) and abdomen+telson length (L A+T) and to register the number of non-ovigerous females (NOF) and ovigerous females (OF). Determining ovarian maturation stages of M. amazonicum was done in a laboratory by observing macroscopic characters such as coloring, size, location and appearance of ovarians examined by transparent carapace. The first maturation age was determined from the relative frequency of the total length (L T) of young and adult females. The environmental parameters of the Jaguaribe River did not hold any influence in the number of individuals collected. A total of 1,337 prawns were sampled, 513 males (38.4 percent) and 824 females (61.6 percent). The proportion between males and females in the studied population was of 1:1.6. Among the collected females, 492 (50.7 percent) did not carry eggs in their abdomens (NOF) and 332 (40.3 percent) carried eggs in their abdomens (OF). There was no record of intact females. Non-ovigerous females with mature ovaries were recorded throughout all the months of collection. The female ovaries were classified as immature (IM), rudimentary (RU), intermediary (IN) and mature (M). M. amazonicum females reach their first sexual maturity between 4.5 and 5.5 cm of total length.

Das espécies de camarão de água doce brasileiras, Macrobrachium amazonicum é a preferida para cultivo, devido ao seu rápido desenvolvimento e fácil manutenção em cativeiro. Este trabalho teve como objetivos caracterizar as fases do ciclo sexual e determinar a idade da primeira maturação de fêmeas de M. amazonicum, coletadas mensalmente, de junho de 2002 a maio de 2003, no Rio Jaguaribe, Itaiçaba, Ceará. Uma amostra de água do local foi coletada mensalmente para determinação dos seguintes parâmetros: temperatura, oxigênio dissolvido, pH e salinidade. Do total de indivíduos capturados mensalmente, uma amostra de fêmeas foi selecionada para determinação do peso total (W T), do comprimento do cefalotórax (L C) e do abdômen+telson (L A+T), e para registro de fêmeas não ovígeras (FNO) e ovígeras (FO). A determinação macroscópica dos estágios de maturação ovariana de M. amazonicum foi realizada pela observação da coloração, do tamanho, da posição e da aparência dos ovários observados por transparência da carapaça. A idade da primeira maturação foi determinada a partir da freqüência relativa de comprimento total (L T) de fêmeas jovens e adultas. Os parâmetros ambientais do Rio Jaguaribe não influenciaram no número de indivíduos coletados. Foram amostrados um total de 1.337 camarões, sendo 513 machos (38,4 por cento) e 824 fêmeas (61,6 por cento). A proporção entre machos e fêmeas na população foi de 1:1,6. Entre as fêmeas coletadas, 492 (50,7 por cento) não carregavam ovos no abdômen e 332 (40,3 por cento) carregavam ovos no abdômen. Não foram observadas fêmeas intactas. Foram registradas fêmeas não ovígeras com ovários maduros durante todo o período de coleta. Os ovários das fêmeas foram classificados como: imaturo (IM), rudimentar (RU), intermediário (IN) e maduro (M). Fêmeas de M. amazonicum atingem a primeira maturação sexual com comprimento total variando entre 4,5 e 5,5 cm.

Functional morphology of the hepatopancreas of Palaemonetes argentinus (Crustacea: Decapoda): influence of environmental pollution

We analyzed the morphological and functional state of hepatopancreas in Palaemonetes argentinusfrom two environments with different pesticide concentrations. Los Padres lagoon (Argentina) is an area subjectedto contamination due to the slow exchange of water, the shallow depth and the input of contaminatedwater. Prawns living in this lagoon accumulate high amounts of organochlorine pesticides in their tissues. Hepatopancreas of prawns from Canal 5, an adjacent shallow stream where the amount of pesticides is belowtoxic levels, and from Los Padres lagoon were processed by standard histological techniques with light microscopyand transmission electronic microscopy. At Los Padres lagoon, we found important tissular alterations,such as intertubular infiltration of haemocytes and connective tissue, epithelial retraction in some tubules, anda folded basal lamina. Important necrotic desquamation, with cariolysis, cariorrexis and lack of cellular detailswere also observed. Numerous tubules presented an enlarged and irregular lumen with the epithelium atrophiedor completely absent. In general, the lesions were particularly located in the medullar region of the organ. Atthe ultrastructural level, R and F cells were the most damaged. Both cell types had nuclear retraction, chromatincondensation and cytoplasmic lysis. Some R cells also had dilated mitochondria and numerous lysosomes, and the basal cytoplasm was nearly completely lysed. The hepatopancreas of prawns from Canal 5 did not evidenceany alterations. The histopathological study of the hepatopancreas is a highly sensitive tool to evaluate thephysiological condition of prawns and water quality. Other environmental conditions were similar, so it can beassumed that pollutants were the main cause of organ deterioration.

Analizamos el estado morfológico y funcional del hepatopáncreas de Palaemonetes argentinus de dosambientes con diferentes concentraciones de plaguicidas. La laguna Los Padres (Argentina) es un área sujeta a contaminación debido al lento intercambio del agua, la escasa profundidad y el influjo de agua contaminada. Las gambas acumulan aquí grandes cantidades de plaguicidasorganoclorados en sus tejidos. Los hepatopáncreas de gambas del Canal 5 y de la laguna Los Padres fueronprocesados mediante técnicas histológicas estándar para microscopía óptica y electrónica de transmisión. Loshepatopáncreas de los individuos recolectados en Los Padres tenían alteraciones tisulares importantes, comoinfiltración intertubular de hemocitos y tejido conectivo, retracción epitelial en algunos túbulos y láminas basalesplegadas. También se observó descamación necrótica importante, con cariolisis, cariorrexis y falta de detallescelulares. Vimos muchos túbulos con un lúmen irregular y agrandado, con el epitelio atrofiado o completamenteausente. En general las lesiones se localizaron en la región medular del órgano. Ambos tipos celulares mostraronretracción del núcleo, condensación de la cromatina y ruptura del citoplasma. Algunas células R también teníanmitocondrias y numerosos lisosomas dilatados, y el citoplasma basal casi completamente desintegrado. Nohallamos alteraciones en los hepatopáncreas de gambas deCanal 5. El estudio histopatológico del hepatopáncreas es una herramienta muy apropiada para evaluar la condiciónfisiológica de las gambas y la calidad del agua. Por la semejanza de otras condiciones ambientales, suponemosque los contaminantes fueron la causa principal del deterioro de los órganos.

Effect of Pseudomonas aeruginosa (MTCC 1688) on the tissue phosphatases activity on Macrobrachium rosenbergii (De Man).

A time course study on the endotoxin toxicity of the gram negative bacteria, Pseudomonas aeruginosa MTCC 1688 on the tissue phosphatases activity on the giant freshwater prawn, Macrobrachium rosenbergii was conducted. The results revealed marked elevation of both acid and alkaline phosphatase activity in the haemolymph and body muscle. The hepatopancreas showed reduced phosphatase activity compared to control. The enzymes, being non-specific in action and particularly the acid phosphatase being of lysosomal origin, their increase in muscle and haemolymph has pathogenic significance in the inoculum treated prawns.

Effects of Hg and Cu on hemocytes-mediated functions in the prawn, Macrobrachium malcolmsonii.

Sublethal effects of Hg (9.6, 14.5 and 24.1 microg/l) and Cu (60.5, 90.8 and 150.5 microg/l) on the hemocytes-mediated functions in the juveniles of the economically important freshwater prawns, Macrobrachium malcolmsonii were investigated. The population of total hemocytes, percentile phagocytosis and superoxide anion production were found to be increased in test prawns exposed to the lowest sublethal concentration of these two metals in comparison to controls. This indicates the fact that a mechanism of host-defence was in an active state to encounter metal toxicity. The total hemocytes population, percentile phagocytosis and superoxide anion production were found to be decreased in test prawns exposed to intermediate as well as the highest sublethal concentrations of Hg and Cu when compared with controls. This suggests that high concentrations of both Hg and Cu have inhibitory effects on the immune functions of the hemocytes in the prawn, M. malcolmsonii.