Revista de Biología Tropical, ISSN: 2215-2075, Vol. 73: e4ahgnf87, enero-diciembre 2025 (Publicado Jul. 28, 2025)

Population structure of freshwater prawn Macrobrachium amazonicum

(Crustacea, Palaemonidae) in two regions of the Amazon River, Brazil

Sting Silva-Duarte1*; https://orcid.org/0000-0001-6878-5762

Jô de Farias-Lima1,2; https://orcid.org/0000-0001-6910-7672

Sheyla Regina Marques-Couceiro1,3; https://orcid.org/0000-0001-8186-4203

1. Postgraduate Program in Tropical Biodiversity, Federal University of Amapá, Macapá, Amapá, Brazil (*Correspondence);

stingduarte@gmail.com

2. Embrapa Amapá, Rodovia Josmar Chaves Pinto, Km 5, n° 2.600, Caixa Postal 10, 68903-419 Macapá, AP, Brazil;

jo.lima@embrapa.br

3. Laboratory of Ecology and Taxonomy of Aquatic Invertebrates of Federal University of West of Pará; sheylacouceiro@

yahoo.com.br

Received 11-VI-2024. Corrected 30-V-2025. Accepted 24-VI-2025.

ABSTRACT

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 speci-

mens. 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.

Keywords: morphometry; sex ratio; white water Amazon shrimp; estuary; river.

RESUMEN

Estructura poblacional del camarón de agua dulce Macrobrachium amazonicum

(Crustacea, Palaemonidae) en dos regiones del río Amazonas, Brasil

Introducción: Macrobrachium amazonicum es una especie de camarón nativa de América del Sur, ampliamente

distribuida y explotada por pescadores artesanales en el Norte de Brasil.

Objetivo: Este estudio tuvo como objetivo analizar la estructura poblacional de M. amazonicum, con énfasis

en la proporción de sexos, distribución de frecuencias de tallas de machos y hembras, considerando también el

período lluvioso y seco en las áreas de estudio.

Métodos: Para ello, se realizaron colectas mensuales de mayo de 2017 a abril de 2018 con la ayuda de «matapis»

en dos localidades, Mazagão e Ilha das Marrecas.

https://doi.org/10.15517/4ahgnf87

INVERTEBRATE BIOLOGY

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INTRODUCTION

The understanding of crustacean popu-

lation variability in different environments

provides information on the habits and charac-

teristics of the species life cycles and how these

are related to the environment, so permitting

an understanding of the ecological stability of

group members, including shrimp (infraorder

Caridea) (Bentes et al., 2016). Such information

provides the basic underpinning for manage-

ment of shrimp aquaculture. Information on

the size distribution of male and female speci-

mens, sex ratio, spatial distribution of indi-

viduals and population age structure can, for

example, be used to explain seasonal variations

in size, reproductive strategies and productive

potential (Silva et al., 2007; Silva et al., 2019).

In this context, population studies on Mac-

robrachium amazonicum (Heller, 1862) are

especially important, as the species is both

scientifically and commercially important in

north and Northeastern Brazil (Alcântara &

Kato, 2016; Costa et al., 2021; Lima et al., 2016;

Melo et al., 2022; Ramos et al., 2016). The spe-

cies is commercially exploited in the states of

Amazonas, Pará and Amapá by artisanal fishing

and indigenous populations (Bentes et al., 2016;

Lima et al., 2014). In general, M. amazonicum

populations are characterized by variations in

the population structure, and there may be dif-

ferences in the distribution of individuals in all

months of the year (Sampaio et al., 2007; Silva

et al., 2019). However, in the Amazon region

fishing pressures on the species may lead led to

unsustainable exploitation (Bentes et al., 2014;

Freire et al., 2012a; Lima et al., 2014; Lucena-

Frédou et al., 2010).

The knowledge of the proportions of the

sexes, sizes and growth stages is important for

effective management and to guarantee sus-

tainable use of M. amazonicum in the Amazon

region. Accordingly, the current study was per-

formed to examine the population structure of

M. amazonicum with emphasis on sex ratio and

size frequency distribution in the regions of the

Amazon river mouth and lower reaches.

MATERIAL AND METHODS

Study area and rainfall data: Samples of

M. amazonicum were collected monthly from

May 2017 to April 2010, on the Mazagão River

(00º15’39.9’’S & 051º20’ 42.3’W), located at the

mouth of the Amazon River, state of Amapá,

and in the Ilha das Marrecas complex on the

lower Amazon River (02º12’19.3’’S & 054º46’

17.9’W), state of Pará (Fig. 1). The shrimps

of the two study sites were pooled for analy-

sis because the areas studied shown relatively

different in their physiography. The Mazagão

River shows various drainage channels, with

varying sizes and depths and daily influence

of the tide, allowing the daily flooding and the

formation of a wide diversity of microhabitats.

The vegetation is typical of the “várzea Ama-

zon”, dense with large and wide bands of mac-

rophytes along the river margin.

In the Ilha das Marrecas, the vegetation is

similar to that observed in the Mazagão River,

with dense, large, and wide bands of macro-

phytes along the Amazon riverbed. However,

thus hydrodynamics is different. In Ilha das

Marrecas, not the daily influence of the tide

only annual variations in the river depth due to

the common floods in the winter period. These

Resultados: Se capturaron un total de 6 796 (4 163 hembras y 2 633 machos), con una media mensual de 531.66

ejemplares. La proporción de sexos en ambas áreas fue favorable a las hembras con 1.32♀ : 1♂ (x² = 76.58,

p < 0.001) en Mazagão y 2.34♀ : 1♂ (x² = 394.26, p < 0.001) en la Ilha das Marrecas. Tanto en Mazagão como en

Ilha das Marrecas, la abundancia estuvo fuertemente relacionada con la precipitación.

Conclusiones: Los camarones de Ilha das Marrecas eran más largos que los capturados en Mazagão. A pesar de

esta presión pesquera en Mazagão, las zonas resultaron favorables para el crecimiento de la especie.

Palabras clave: morfometría; proporción de sexos; camarón blanco del Amazonas; estuario; río.

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natural floods cause cycles of erosion, trans-

portation and deposition of sediments, with

systematic annual morphological modification

of the riverbed (Farias & Carneiro, 2012).

Both areas have a humid Equatorial cli-

mate, with two seasonal periods marked by a

rainy period from December to June and a less

rainy (dry) period from July to November. To

assist the study with updated data on local sea-

sonality, monthly data on rainfall were obtained

from the website of the Instituto Nacional de

Meteorologia (INMET, 2021).

Shrimp collection: For the collection of

the shrimp 20 traps locally known as “matapis”

were used. Traps were set and submerged over

Fig. 1. The location of Macrobrachium amazonicum captures areas in the mouth and lower Amazon between May 2017

and April 2018, and July 2021 to May. The black circle ( ) represents Mazagão, while the green triangle (p) represents

Marrecas Island.

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a single nocturnal tidal cycle (12 hours). All

captures occurred at daybreak. They were then

recovered one at a time and the contents were

removed, placed in plastic bags, labeled, stored

on crushed ice in a cooler, and transported to

the laboratory.

Shrimp Analysis: In the laboratory,

shrimps were identified, sexed and submitted

to biometrics. Taxonomic identification follow-

ing the taxonomic keys of Melo et al. (2003).

Sex was verified by the presence of masculine

appendix on the second pleopod. To biometrics

standard length (SL-linear distance from the

base of ocular orbit to the base of the telson)

and total wet mass (TM) of shrimps a digital

caliper (0.01 mm precision) and a digital scale

(0.01 g), were used to measure, respectively.

Individuals with measures below the small-

est identifiable male will be considered sexu-

ally undifferentiated, while shrimps with sizes

below the smallest female egg will be consid-

ered juveniles (Lima et al., 2014).

The monthly rainfall data of each region

was obtained at the data of base the INMET

(2021).

Data analysis: The statistical analysis of

the data was performed with the aid of the

BioEstat 5.0® software (Ayres et al., 2007). Nor-

mality and homoscedasticity of the variances

were tested with Shapiro-Wilk and Bartlett’s

tests, respectively.

The sex ration was determined per month

in each collection site using the chi-square

test (x², α = 0.05) according to Zar (1999).

The t-test was applied to verify differences sex

ration between collection sites. Kruskall-Wallis

test was applied to verify differences between

standard length of males and females during

the studied period. The t-test was applied to

verify differences regarding standard length

between sex and collection sites. All analysis

p-value equal or less than 0.05 were chosen

to indicate statistical significance. To verify if

there is a relationship between rainfall and the

abundance of prawn by area, one regression

analysis was performed (Zar, 1999).

RESULTS

A total of 6 796 shrimps were caught, of

which 4 132 (60.8 %) were in Mazagão and 2

664 (39.2 %) in Ilha das Marrecas. The total

number of shrimps caught in Mazagão was

higher than in Ilha das Marrecas (p < 0.05) in

most study months, except in June and April

2018 (Fig. 2). In general, the M. amazonicum

catch was higher during the period with less

rain (July to October), particularly for adult

shrimps (Fig. 2, Fig. 3).

Fig. 2. Abundance of M. amazonicum (Heller, 1862) collected between May 2017 and Apr 2018 in the mouth of Mazagão

River-AP and Ilha das Marrecas-PA; and their relationship with rainfall.

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Chi-square test showed that the sex ratio

was significantly different from 1:1 in Ilha das

Marrecas (x² = 394.26, p < 0.001) and Mazagão

(x² = 76.58, p < 0.001), being 2.34♀ : 1♂ and

1.32♀ : 1♂ respectively. In Mazagão, M. amazo-

nicum showed significant differences in relation

to the expected sex ratio except in the months,

May, July, August and September of 2017 and

January of 2018. In contrast, in Ilha das Mar-

recas, sex ratio differences were observed in all

collection months (Table 1).

In both study areas monthly distribution

of adult juveniles, males, and females showed

season variation (Fig. 3A, Fig. 3B). In Maza-

gão, numerical dominance of male and adult

female shrimps alternated in both seasons.

Adult male shrimps dominant in May, July,

August, September, and adult female shrimps

from December to April (rainy season). While

in Ilha das Marrecas, adult female shrimps were

not only more abundant than the adult males

in the rainy season (January to April), but also

across most of the period with little rain (July

to December).

Juvenile shrimps were found in all months

of the year, in both regions, with a recruitment

peak in June and July (Mazagão) and June, Sep-

tember, October and March (Marrecas), with

juveniles comprising between 35 % and 45 % of

the catch (Fig. 3A, Fig. 3B).

In Mazagão, male shrimps of the length

class 43.4 mm to 49.4 mm were commonest

while most female shrimps were between 49.4

mm and 55.4 mm. In Ilha das Marrecas, male

Fig. 3. Monthly absolute frequency distribution of juvenile, adult males and adult females of M. amazonicum (Heller, 1862)

collected between May 2017 and Apr 2018. A. in the mouth of Mazagão River-AP. B. in Ilha das Marrecas-PA.

6Revista de Biología Tropical, ISSN: 2215-2075 Vol. 73: e4ahgnf87, enero-diciembre 2025 (Publicado Jul. 28, 2025)

and female shrimps were most common in the

length classes 61.4 mm to 67.4 mm and 49.5

mm to 55.4 mm, respectively (Table 2). Analy-

sis of variance showed significant differences

in the standard lengths of males, females and

total shrimp lengths between the sites, but not

between collection months (Fig. 4).

Males captured in Ilha das Marrecas had

a higher mean length than those captured in

Mazagão in May and October 2017 and Feb-

ruary and April 2018 (Fig. 4A). Additionally,

females caught in Marrecas had longer mean

lengths than those caught in Mazagão between

June and September 2017 and March and April

Table 2

Frequency distribution of shrimps M. amazonicum in size classes (CP), collected between May 2017 and April 2018 in

Mazagão-AP and ilha das Marrecas.

Classe

(CP, mm)

Mazagão Ilha Marrecas

Adult

Males

Adult

Females

Juveniles

Males

Juveniles

Females

Adult

Males

Adult

Females

Juveniles

Males

Juveniles

Females

31.4-37.4 - - 70 123 - - 70 125

37.4-43.4 276 345 - - - 64 110

43.4-49.4 469 361 - - 25 165 - -

49.4-55.4 237 601 - - 107 638 - -

55.4-61.4 303 529 - - 125 499 - -

61.4-67.4 202 315 - - 206 235 - -

67.4-73.4 112 15 - - 50 59 - -

73.4-79.4 111 2 - - 51 56 - -

79.4-85.4 7 5 - - 15 18 - -

85.4-91.4 10 14 - - 12 11 - -

91.4-97.4 7 10 - - 10 6 - -

97.4-03.4 0 8 - - 5 2 - -

Total 1 734 2 205 70 123 606 1 689 134 235

Table 1

Chi-square values and sex ratio of M amazonicum sampled in Mazagão and Ilha das Marrecas between May 2017 and April

2018.

Months Mazagão Ilha das Marrecas Group Areas

♀ ♂ x² Ratio ♀ ♂ x² Ratio ♀ ♂ x² Ratio

may/17 131 136 2.63 0.82:1 91 32 28.30 2.8:1* 216 184 2.6 1.17:1

jun/17 143 33 0.49 1.14:1* 350 115 118.76 3.04:1* 404 162 103.5 2.49:1*

jul/17 153 172 1.80 0.88:1 130 90 7.27 1.44:1* 413 342 6.7 1.20:1*

aug/17 220 221 0.08 0.97:1 172 108 14.63 1.59:1* 398 340 4.6 1.17:1*

sep/17 290 236 7.81 1.26:1* 354 184 53.72 1.92:1* 666 430 50.8 1.54:1*

oct/17 456 320 21.40 1.5:1* 152 50 51.50 3.04:1* 473 264 59.3 1.79:1*

nov/17 220 50 11.11 1.76:1* 90 38 21.31 2.36:1* 182 90 31.1 2.02:1*

dec/17 299 138 64.51 2.23:1* 79 19 36.73 4.15:1* 388 158 96.9 2.45:1*

jan/18 82 59 2.99 1.31:1 58 15 25.33 3.86:1* 150 85 18.0 1.76:1*

feb/18 186 112 17.52 1.60:1* 67 27 17.02 2.48:1* 265 150 31.9 1.76:1*

mar/18 176 101 17.28 1.63:1* 74 21 29.57 2.48:1* 260 135 39.6 1.92:1*

apr/18 147 51 0.45 087:1* 88 27 32.36 3.25:1* 138 84 13.1 1.64:1*

*Significant differences from the chi-square test, p < 0.05.

Revista de Biología Tropical, ISSN: 2215-2075, Vol. 73: e4ahgnf87, enero-diciembre 2025 (Publicado Jul. 28, 2025)

Fig. 4. Monthly variation of standard length between males, females and grouped sex of M. amazonicum collected in the

Mazagão River-AP and Ilha das Marrecas -PA, between May 2017 and Apr 2018. A. Males. B. Females and C. Grouped

sex. Different lower letters represent significant differences between the collection sites, while different upper-case letters

represent differences between the months.

8Revista de Biología Tropical, ISSN: 2215-2075 Vol. 73: e4ahgnf87, enero-diciembre 2025 (Publicado Jul. 28, 2025)

2018 (Fig. 4B). In the months of November and

December 2017 and January 2018 (Fig. 4C),

mean length for all shrimps captured in Maza-

gão exceeded those from Ilha das Marrecas.

DISCUSSION

Macrobrachium amazonicum was more

abundant in Mazagão than in Ilha das Marre-

cas, except in the months of June 2017 and April

2018. In general, the coastal areas of the Ama-

zon show a greater abundance of this species

compared to more continental sites (Lima et

al., 2014; Meireles et al., 2013). This difference

in abundance may be linked to the amount of

suspended organic matter and nutrients avail-

able. This is a consequence of differences in

the intensity of tidal activity and bioturbation,

which favor the development of a remarkable

productivity of micro invertebrates, algae and

fine particulate organic matter in more coastal

areas. Another aspect is the proximity of estua-

rine areas to the oceanic itself. Macrobrachium

amazonicum is an eurihaline species, tolerating

a wide range of salinity, but with larva which

develop best in waters with a particular salinity

concentration, as shown by a number of labora-

tory studies (Araujo & Valenti, 2010; Perroca et

al., 2022; Soeiro et al., 2016; Sterzelecki et al.,

2021). Despite tolerating a wide concentration

of salinity as adults, there are changes in the

larval stages of this species, which include mor-

phological changes in the gills and expression

of the sodium and potassium ATPase pump

(Na+, K+ ATPase-NKA), which reduce larval

survival at low salinities (Boudour-Boucheker

et al., 2013). Thus, M. amazonicum populations

in estuarine areas have better conditions to

complete their larval development than popula-

tions from more continental sites.

Differences in abundance between sea-

sonal periods is a particular trend of each spe-

cies in the genus Macrobrachium: M. brasiliense

(Heller, 1862) (Mantelatto & Barbosa, 2005),

M. macrobrachion (Herklots, 1851) and M.

vollenhovenii (Herklots, 1857) (Lawal-Are &

Owolabi, 2012) all display greater rainy sea-

son abundance, unlike M. iheringi (Ortmann,

1897), M. ohione (Smith, 1874) (Truesdale &

Mermilliod, 1979), M. tenellum (Smith, 1871)

(Román-Contreras, 1979), M. olfersi (Wieg-

mann, 1836) (Mossolin & Bueno, 2003) and M.

amazonicum, which are clearly more abundant

during the less rainy season.

Data for the current study followed this

pattern, so that in both Mazagão and Ilha

das Marrecas, abundance was strongly related

to precipitation, with highest catches during

the less rainy season (July to October). These

results corroborate data from other parts of the

Amazon which show reproductive peaks of M.

amazonicum coinciding with the rainy season

period (Lima et al., 2014; Melo et al., 2022), and

the recruitment period coinciding with the dry

season (Bentes et al., 2016; Costa et al., 2016;

Costa et al., 2021).

In the current study, a predominance of

females was observed at both study sites. This

bias seems to be common in the genus Macro-

brachium (dos Santos-Antunes & Oshiro, 2004;

Fransozo et al., 2004; Meireles et al., 2013; Melo

et al., 2022). It has been reported for estuarine

and coastal populations of M. amazonicum in

the Amazon region (Freire et al., 2012b; Lima et

al., 2014; Montoya, 2003; Sampaio et al., 2007;

Silva et al., 2007). However, an excess of males

(Mantel & Dundgeon, 2005) and equal male :

female ratios (Mattos & Oshiro, 2009) have also

been observed for the genus.

Although a predominance of females was

common, the monthly mean sex ratio values in

favor of females was higher in Marrecas than in

Mazagão, while in some months no significant

differences were observed. In crustaceans devi-

ations in the sex ratio may be a consequence

of many factors, including between-sex differ-

ences in size, mortality, and hatching rates. But

factors such as development rates, dispersion,

reproduction, differential migration, environ-

mental conditions, geographic characteristics

and anthropogenic interference may also be

influential (Botelho et al., 2001; Lima et al.,

2014; Perroca et al., 2022; Sterzelecki et al.,

2021). As the environmental characteristics and

availability of nutritional resources are similar

between the two study areas, it is likely that the

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greater abundance of females in Marrecas is

related to the reproductive strategy adopted by

M. amazonicum populations in each region. In

Marrecas, there is a clear reduction in the avail-

ability of salinity and there is little tidal influ-

ence, thus an increase the number of females

there means that a larger number of larvae

are available to close their cycle and increase

the availability of juveniles for dispersion, so

maintaining the population (Bentes et al., 2016;

Silva et al., 2019).

The unplanned, unmanaged and intensive

exploitation of these shrimps is another fac-

tor that may be related to sex ratio changes,

as observed in populations of M. amazonicum

from the island of Combú in Pará State, Brazil

(Lucena-Frédou et al., 2010; Silva et al., 2002).

However, in Ilha das Marrecas, where fishing

pressure is currently very low compared to

Mazagão, the sex-ratio distortion cannot be

attributed to this fact. Instead, it is likely to

be associated with the fact that the M. ama-

zonicum population on the lower Rio Tocan-

tins (State of Pará), became isolated after the

construction of a dam. This appears to have

strongly affected the shrimps, resulting in a

reduction in the average size of the captured

specimens and a doubling of sex ratio in favor

of females (Odinetz-Collart, 1991).

For the biometric variables, young and

adult shrimp caught in Ilha das Marrecas had a

greater standard length than the those caught in

Mazagão, except in November and December

2017 and January 2018 (Fig. 4C). As climatic,

environmental and nutritional conditions are

similar between Ilha de Marrecas and Mazagão,

this difference is most likely explained by fish-

ing pressure, which is substantially higher in

the region of the mouth at the Amazon River

where Mazagão occurs than in the lower river

Amazonas, where the Ilha das Marrecas lies.

As observed previously, high fishing pressure

can alter M. amazonicum population structure

and dynamics, especially the size and sexual

proportion (Lucena-Frédou et al., 2010; Melo

et al., 2022; Silva et al., 2002). Comparing our

results with other studies, it appears that the

average size of the shrimp caught in Mazagão

is similar to that reported in studies at other

estuarine sites in the Amazon region (Bentes

et al., 2011; Costa et al., 2021; Silva et al., 2002;

Silva et al., 2007), while size of shrimp caught in

Ilha das Marrecas were similar in that of those

caught in more coastal areas (Borges, 2003) and

in reservoir areas such as Rômulo Campos in

Bahia State, Brazil (Costa et al., 2016).

For recruitment it was apparent that young

shrimps constantly entered the population

every month. However, there were months

when these individuals were more abundant

(June and July in Mazagão; June, September,

October and March in Ilha das Marrecas). The

presence of juvenile shrimps throughout the

year in both study areas suggests that M. ama-

zonicum has continuous recruitment. A contin-

uous pattern of recruitment was also observed

in estuarine and continental populations in Ilha

de Combu in Pará state (Lucena-Frédou et al.,

2010), in Guajará Bay, Pará (Bentes et al., 2011),

in the reservoir of the Miranda hydroelectric

power-plant, Rio Araguari in Minas Gerais

state (Silva, 2014). The continuous recruitment

of juveniles at the two study sites likely reflects

the reproductive strategy of M. amazonicum

adopted in each region. In both areas, a pre-

dominance of females was observed, with con-

tinuous reproduction, reflecting the constant

recruitment of youngsters (Rocha et al., 2023;

Ventura et al., 2019).

In the Amazon region, shrimps are mainly

exploited with traps popularly known as mata-

pís (Costa et al., 2016). Such traps are usu-

ally produced with jupati palm (Raphia vinifer)

splint, with have very small gaps between the

splints (three millimeters on average) that allow

the capture of shrimp in the immature stages or

early in maturation (Lima, 2014). This fact was

shown in Mazagão and in Ilha de Marrecas,

where shrimps below the size at first matura-

tion were captured in all months of the study.

Evidence of similar current fishing impacts on

the M. amazonicum population was reported

from the ilha de Combú, Pará state (Silva et al.,

2007), and at the mouth of the Amazon River in

the state of Amapá (Lima, 2014). At both sites

matapi fishing is affecting local M. amazonicum

10 Revista de Biología Tropical, ISSN: 2215-2075 Vol. 73: e4ahgnf87, enero-diciembre 2025 (Publicado Jul. 28, 2025)

populations (Lucena-Frédou et al., 2010), and

negatively implicating the natural stocks of the

species in the region.

Based on our results of juvenile-stage cap-

ture and data presented by Camargo et al.

(2009), it is highly likely that the splint-sepa-

ration distance of 2.0 mm to 5.0 mm currently

used by artisanal fishermen in the Amazon

region is not appropriate. For M. amazonicum

the length at first maturation (between 45.0

mm and 60.0 mm) reported by Guest (1979),

Moraes-Riodades and Valenti (2002), Sampaio

et al. (2007), Lima et al. (2014) and Bentes et al.

(2014) is lower than those found in Mazagão

and Ilha das Marrecas, indicating that shrimp

fishing in these areas has not yet reached the

level of exploitation reported at other sites.

Given the results of the current study, it is

recommended that the minimum spacing of

1 cm between the matapís splints be adjusted

downwards, a proposal already made for M.

amazonicum by both Camargo et al. (2009)

and Lima (2014). In an attempt to reduce fish-

ing pressure, studies such as Camargo et al.

(2009) and Lima (2014) have suggested changes

in traps and capture strategies. In addition

to changing in the distance between matapí

splints, these authors suggest that the local

and state authorities, who police the environ-

ment, implement and monitor an active fishery

management policy for the species. This should

include setting the size between 60 and 70

mm (first maturation) as the lower catch size

limit for the species in the estuary region. For

Mazagão and Ilha das Marrecas, we can see that

such catch limits would also be appropriate.

Such a measure would result in a considerable

increase in the number of breeding specimens

and, consequently, an increase in the size of

shrimp caught later, generating more income

for fishermen and merchants, as well as greater

satisfaction for consumers, who will be able

to purchase larger products, which are more

attractive to consumers.

M. amazonicum showed variations in the

pattern of population structure in Mazagão

and in the Ilha das Marrecas. In Mazagão a

greater abundance of specimens was observed.

In relation to females, in Mazagão and in the

Ilha das Marrecas, they were significantly larger

and heavier than males, denoting differentiated

metabolism, probably due to reproduction, in

addition, a predominance of females and varia-

tion between the average length was observed

indicating that the populations of Mazagão and

Ilha das Marrecas are distinct. In both areas

M. amazonicum showed a reproductive peak

closely related to the rainy season, however,

the species reproduction occurs continuously

throughout the year.

Ethical statement: The authors declare

that they all agree with this publication and

made significant contributions; that there is no

conflict of interest of any kind; and that we fol-

lowed all pertinent ethical and legal procedures

and requirements. All financial sources are fully

and clearly stated in the acknowledgments sec-

tion. A signed document has been filed in the

journal archives.

ACKNOWLEDGMENTS

To the Coordenação de Aperfeiçoamento

de Pessoal de Nível Superior (CAPES) for

the Master’s scholarship granted to the first

author. To the Conselho Nacional de Desen-

volvimento Científico e Tecnológico (CNPq)

for the financial support according to process

no. 407698/2013-2, process no. 444367/2014-4,

process no. 405234/2024-4 and Fapeap (Call

003/2022-# 193). To the Empresa Brasileira de

Pesquisa Agropecuária for structural and logis-

tical support for data analysis. To the Ministério

do Meio Ambiente - MMA and Instituto Chico

Mendes de Conservação da Biodiversidade -

ICMBio for Permanent license for collection of

zoological material n° 24578-2.

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