Dilocarcinus Pagei Research Articles

Astaxanthin improves lipotoxicity, lipid peroxidation and oxidative stress in kidney of sucrose-rich diet-fed rats

Metabolic Syndrome (MS) is a cluster of metabolic risk factors, characterized by abdominal obesity, dyslipidemia, hypertension, insulin resistance, among others. The purpose of the study was to evaluate the astaxanthin (AXT) effects extracted from freshwater crab (Dilocarcinus pagei) at the Paraná Basin on lipotoxicity, lipid peroxidation and oxidative stress in the kidney of rats fed with a sucrose-rich diet (SRD). We hypothesized that daily administration of AXT prevents kidney damage by reducing lipotoxicity, lipid peroxidation, and reactive oxygen species (ROS), and by improving antioxidant enzyme defenses and crosstalk between NrF2 and NF-ĸB transcription factors. Male Wistar rats were fed a reference diet (RD), RD+AXT, SRD and SRD+AXT (AXT daily oral dose: [10 mg/kg body weight]) for 90 days. Systolic and diastolic blood pressure, biochemical assays in serum and urine were evaluated. Renal cortex samples were taken for histological analysis, determination of triglyceride content, ROS, thiobarbituric acid reactive substances (TBARS), catalase (CAT), glutathione peroxidase (GPx) and glutathione reductase (GR) enzyme activities and glutathione content (GSH). 4-HNE, NrF2, and NF-ĸB p65 expression were analyzed by immunohistochemistry. We demonstrated that daily oral supplementation of AXT to animals fed a SRD reduced systolic and diastolic blood pressure, histological renal damage, lipid accumulation, ROS and lipid peroxidation, and increased CAT and GPx activities. NrF2 protein expression in renal cortex was increased, whilst NF-ĸB p65 was reduced. AXT extracted from freshwater crabs (Dilocarcinus pagei) may be promising nutritional strategy for the prevention of renal alterations present in this model.

Non-Native Decapods in South America: Risk Assessment and Potential Impacts

Biological invasions pose significant challenges in the Anthropocene, impacting ecosystem biodiversity and functioning. Ecological Niche Modeling is widely used to evaluate potential areas at risk of invasions, aiding in the prevention of invasive-species expansion and guiding conservation efforts in freshwater ecosystems. The main objectives of this study were to model the ecological niche and evaluate remaining suitable habitat areas for the occurrence of five potentially invasive species of freshwater decapods in South America: Dilocarcinus pagei, Macrobrachium amazonicum, M. jelskii, M. rosenbergii, and Procambarus clarkii. Occurrence data from the Global Biodiversity Information Facility were complemented with a literature systematic review. Variables used in the models were obtained from the Worldclim and EarthEv databases. Ecological Niche Modeling was performed using the Biomod2 and sdm package algorithms. Our results indicated a suitable area of up to 11% of South America. Model evaluations yielded favorable TSS and AUC values (>0.7 and >0.8). The suitable areas projected for South America included several hydrographic basins and Protected Areas. The information generated in our study can help identifying areas susceptible to decapod invasion in South America and support local management and decisions.

Sustainable production of astaxanthin from Dilocarcinus pagei crab and optimisation of its extraction with edible oils

Dilocarcinus pagei is a South American crab commonly found in fishponds. As crabs are a source of astaxanthin (AST) and food inputs, this preliminary research aimed at studying the composition of females and males of this species to assess its potential for commercial applications, and at optimising the extraction of AST with edible oils to promote its use as an ingredient for the nutraceutical, pharmaceutical and feed industries. The chemical composition differed between males and females only in moisture, and the values obtained were: 65.4 ± 1.0% and 72.5 ± 3.1% moisture, 45.7–40.3% d.m. minerals, 22.0–24.1% d.m. fibres, 18.2–17.4% d.m. proteins, and 10.4–11.1% d.m. lipids. The Box-Behnken design was applied and validated for extraction with soya bean and sunflower oils, adjusting the oil:crab ratio, temperature, and extraction time. The optimal conditions found consisted of 140 mL/g, 90 °C and 170 min for soya bean oil, reaching an accumulation of AST of 50 ± 5 μg/g crab d.m. For sunflower oil, the conditions were 60 mL/g, 90 °C and 161 min, reaching 31 ± 3 μg/g crab d.m. Finally, the amounts of AST obtained using soya bean oil were higher than those obtained using sunflower oil; thus, soya bean oil would be recommended as a solvent to extract the pigment.

From color to shape: ontogenetic shifts in traits of the freshwater crab Dilocarcinus pagei (Brachyura: Trichodactylidae)

Crustaceans usually undergo a series of changes after the puberty molt. These changes are often associated with size increases in the body and in structures such as the abdomen and claws so that they can achieve higher reproductive fitness. These morphological changes allow the animal to fight, court, and signal for its conspecific with better performance. To compare ontogenetic changes, we used the freshwater crab Dilocarcinus pagei Stimpson, 1851 as a model. We analyzed differences in carapace and claw shape, force generation (via the apodeme area), morphological integration of claws, and color changes among demographic groups. Adult crabs had an increase in claw and carapace size followed by a shape change that makes the claws more robust. In addition, the animals changed from a dark brown coloration in juveniles to a dark red coloration in adult males, while adult females presented a dark red-brown coloration. Presumably, phenotypic changes may enhance crabs’ ability to obtain different food sources, as well as fight for sexual partners, and manipulate females during courtship. Color changes can be a strategy by which adult males can signal to females, while the dark brown coloration of juveniles can help in camouflage in the substrate.

Population biology of the freshwater crab Dilocarcinus pagei Stimpson, 1861 (Decapoda: Trichodactylidae) in the Araguari River, south-eastern Brazil

ABSTRACT Dilocarcinus pagei is a freshwater crab that has a wide distribution in South America, occurring in the main river basins of Brazil. Our study analysed some aspects of the population biology of D. pagei in a population that occurs in the Araguari River, in south-eastern Brazil. Crabs were sampled between September 2020 and November 2021. The population structure was analysed according to the organisms’ size, sex and life stage. The frequency of demographic groups (adults and juveniles) over months was assessed using an environmental gradient analysis and a canonical correspondence analysis (CCA). A total of 392 crabs were collected, 282 males and 110 females. Male crabs were more abundant during most of the sampling period. Thus, the sex ratio in general and for most months was biased towards males. Gradient and CCA analyses showed seasonality in the occurrence of ovigerous females. This demographic group was more frequently sampled when the local rainfall increased. Our study provides relevant information about the population and reproductive biology of D. pagei, which may contribute to the understanding of the reproductive traits of freshwater crabs and also the ecological role of this species in the environments it inhabits.

LIVE BAIT TRADE AS A PATHWAY FOR THE INTRODUCTION OF NON-NATIVE SPECIES: THE FIRST RECORD OF Dilocarcinus pagei IN THE PARANAPANEMA RIVER BASIN

Brazil has one of the most significant diversity of freshwater fish in the world, and this drives trade and fishing tourism. Several species of sport fish have characteristics and behaviors that favor fishing tourism and its related activities. Live baits are widely used in fisheries across the country, and at the end of fisheries, is common that anglers may release the remaining bait in rivers, lakes or reservoirs. Here we report for the first time the crab Dilocarcinus pagei in the Paranapanema River basin, and list the freshwater species that were introduced similarly. During field samplings between 2012/2016, and 2018/2019, we captured 10 individuals of D. pagei. One female in the Rosana Reservoir; and two juveniles, one female and six males in the Taquaruçu Reservoir. The literature review revealed 16 species used as live bait, the crab D. pagei and 15 fish species. Gymnotiformes were the largest number of species used as live bait. The basins that had introduction cases were in the Upper Paraná, Iguaçu, and Paraíba do Sul Rivers. The Paraguay-Lower Paraná River was the system that contributed with nine species to the most invaded ecoregion in Brazil, the Upper Paraná River basin. Anglers and live bait farmers should be aware of the risks and consequences of these constant introduction actions (propagule pressure), not releasing baits. In addition, the live bait trade must be monitored and controlled to occur only with species in their original river basin.

Comparative morphology of the spermatophores and spermatozoa of three Amazon freshwater crabs (Decapoda, Brachyura, Trichodactylidae)

ABSTRACT The ultrastructure of spermatophores and spermatozoa of freshwater crabs are little known, and a description of characters unique to this taxon is lacking. In this study, we describe and compare the ultrastructure of spermatophores and spermatozoa of Dilocarcinus pagei, Zilchiopsis oronensis and Valdivia serrata. In addition, we perform a comparative analysis with other freshwater crab species described in the literature. All species studied presented predominantly coenospermic spermatophores, in addition Z. oronensis and V. serrata also presented some cleistospermic spermatophores; which are described here for the first time in Trichodactylidae. The spermatozoa of the three species share a pattern found in the Brachyura, however, we found common traits for Trichodactylidae. The operculum is thick, protruding and imperforate with the presence of a prominent subopercular ring. The shape of the operculum is roundish in D. pagei and more triangular in Z. oronensis and V. serrata. The perforatorial chamber is panduriform in D. pagei and Z. oronensis, and oblong in V. serrata. The membrane of the perforatorial chamber in D. pagei has numerous shallow corrugations and short perforatorial filaments, while Z. oronensis and V. serrata have fewer, almost indistinguishable corrugations and long perforatorial filaments. All three species have a marked lateral expansion of the base of the perforatorial chamber and overall truncation of the acrosome vesicle, in Z. oronensis and V. serrata, absence of an acrosome ray zone, developed thickened ring and a thick nucleo-cytoplasmic plate, being obviously lamellar in D. pagei and homogeneous in Z. oronensis and V. serrata. The spermatozoa presents similar characteristics between Trichodactylidae and other freshwater crab families opening the possibility of unit all heterotreme freshwater crab families as a single group. The probably Trichodactylidae autapomorphies, that diverges from all other freshwater crabs, reinforce the hypothesis that the trichodactylids derived later as an independent lineage of freshwater crabs.

Thermal stability of astaxanthin in oils for its use in fish food technology

Astaxanthin is one of the inputs that most influences the final prices of salmonids on the market and is unstable due to its sensitivity to various factors, such as temperature, which cause the loss of its bioactivity during feed processing and storage. Dilocarcinus pagei is a native crab that is commonly found in fish culture ponds and presents an attractive reddish-brown coloration. The objectives of the present study were to evaluate this crab as a natural source of astaxanthin and to assess how the stability of this pigment was affected by different vegetable oils (soy and sunflower) and butylhydroxytoluene (BHT) presence over a range of temperatures used in feed processing technology like extraction, cooking, extrusion and storage. Individuals of D. pagei were collected and homogenized. Carotenes were extracted from different samples using acetone. The extractions were analyzed using High-Performance Liquid Chromatography (HPLC). The percentages of remaining astaxanthin dissolved in soy and sunflower oils with or without BHT (0.1%) were estimated before and after being incubated at 50 °C. Astaxanthin dissolved in both oils with BHT were exposed to different temperatures between 25 °C and 180 °C. Samples were taken at different intervals of time and astaxanthin was measured at λmax490 nm by a spectrophotometer. The degradation rate of astaxanthin at each temperature in both oils was estimated. The results showed that D. pagei would be an alternative as a natural source of astaxanthin since its concentration values (231.5 μg/g dry matter) are similar to those present in other species commercially exploited. The two-ways Analysis of variance (ANOVA) showed that the presence of BHT (P = 0.03) and the oils (P < 0.01) used as dissolvent affect the percentages of remaining astaxanthin independently of the oil used (P = 0.06). The astaxanthin degradation rates in sunflower were higher than those in soy oil at all tested temperatures, being significantly different (P < 0.05) at temperatures from 25 °C to 120 °C but not at 180 °C. The activation energies calculated for soy oil was 88.7 kJ/mol while for sunflower oil, it was 85.5 kJ/mol. Astaxanthin was more stable in soy oil than in sunflower oil. Moreover, commercial soy oil is a cheap ingredient and a good source of unsaturated fatty acids (ω3, ω6 and ω9). Thus, soy oil would be recommended as a solvent to extract the pigment.

Amazon freshwater crab Dilocarcinus pagei (Decapoda: Trichodactylidae): a view about burrow construction behavior

Crabs use burrows to prevent predation, environmental interference and shelter. The present study investigated the excavation behavior of the trichodactylid crab Dilocarcinus pagei, considering the biometric aspects of the burrows, the excavation time, the amount of bioturbation and the excavation behavior of the two sexes. The burrows of males had a mean diameter larger than the females, although the depth was similar for both sexes. Females had higher bioturbation than males, and showed enlargement in a camera format at the bottom, even closing the entrance of the burrows with a "plug" after their construction. Both the camera and the presence of the "plug" in the burrows of the females may be associated with reproduction. The presence of pellets observed at the entrance of burrows is associated with the cleaning of the pereiopods by crabs after the excavation. The sequence of behaviors for the construction of the burrows is described in detail, contributing to the knowledge about the biology and ecology of freshwater crabs of the Amazon.

Contrasting strategies of osmotic and ionic regulation in freshwater crabs and shrimps: gene expression of gill ion transporters.

Owing to their extraordinary niche diversity, the Crustacea are ideal for comprehending the evolution of osmoregulation. The processes that effect systemic hydro-electrolytic homeostasis maintain hemolymph ionic composition via membrane transporters located in highly specialized gill ionocytes. We evaluated physiological and molecular hyper- and hypo-osmoregulatory mechanisms in two phylogenetically distant, freshwater crustaceans, the crab Dilocarcinus pagei and the shrimp Macrobrachium jelskii, when osmotically challenged for up to 10 days. When in distilled water, D. pagei survived without mortality, hemolymph osmolality and [Cl-] increased briefly, stabilizing at initial values, while [Na+] decreased continually. Expression of gill V-type H+-ATPase (V-ATPase), Na+/K+-ATPase and Na+/K+/2Cl- symporter genes was unchanged. In M. jelskii, hemolymph osmolality, [Cl-] and [Na+] decreased continually for 12 h, the shrimps surviving only around 15-24 h exposure. Gill transporter gene expression increased 2- to 5-fold. After 10 days exposure to brackish water (25‰S), D. pagei was isosmotic, iso-chloremic and iso-natriuremic. Gill V-ATPase expression decreased while Na+/K+-ATPase and Na+/K+/2Cl- symporter expression was unchanged. In M. jelskii (20‰S), hemolymph was hypo-regulated, particularly [Cl-]. Transporter expression initially increased 3- to 12-fold, declining to control values. Gill V-ATPase expression underlies the ability of D. pagei to survive in fresh water while V-ATPase, Na+/K+-ATPase and Na+/K+/2Cl- symporter expression enables M. jelskii to confront hyper/hypo-osmotic challenges. These findings reveal divergent responses in two unrelated crustaceans inhabiting a similar osmotic niche. While D. pagei does not secrete salt, tolerating elevated cellular isosmoticity, M. jelskii exhibits clear hypo-osmoregulatory ability. Each species has evolved distinct strategies at the transcriptional and systemic levels during its adaptation to fresh water.

Color variation of the freshwater crab Dilocarcinus pagei Stimpson, 1861 captured in the Amazon region at Itacoatiara, Amazonas, Brazil

ABSTRACT The relationship between color and size supports the hypothesis that color is an important signal for some crab species during mating rituals or agonistic interactions. Thus, the objective of this study was to describe the color variation of D. pagei and its relationship with sex and sexual maturity. The crabs were placed on a surface for photographic recording of the body parts: cephalothorax, chelipeds, abdomen and pereiopods using a digital camera installed on a photographic table. Images were converted to the spectrum of red, green, blue and also of them combined (RGB). The values of each spectrum revealed that the color variation of the cephalothorax and chelipeds were different between adults and juveniles. The abdomen and pereiopods showed color variation in both sexes and at developmental stages. The pattern of color variation observed in juveniles ranged from light to dark brown and adults are from orange to intense red. The change in color of the cephalothorax and chelipeds could be used as a character to determine the onset of sexual maturity. The high color variation of the abdomen and pereiopods in both sexes and at developmental stages, though, indicates individual variation which probably is associated with other factors, such as molt stage or even the quality of food available.

Desiccation tolerance of two freshwater crabs of the Amazon: Dilocarcinus pagei and Sylviocarcinus pictus (Decapoda, Trichodactylidae)

Abstract This study investigated the resistance to desiccation of two species of freshwater crabs, Dilocarcinus pagei and Sylviocarcinus pictus. Dilocarcinus pagei survived almost twice as long as S. pictus, 127 ± 82.4 h and 69 ± 17.5 h, respectively. The females of both species survived longer than the males and the females of D. pagei survived longer than the females of S. pictus. Water loss until death was on average 30.12 ± 11.79% for D. pagei and 42.59 ± 7.49% for S. pictus. Dilocarcinus pagei showed a lower water loss than S. pictus until death and large S. pictus females and small D. pagei females exhibited a higher water loss, with differences between species and sex. The results reveal how these two species of crabs behave in extreme droughts in the Amazon floodplain. The females of both species were more resistant, although females of D. pagei were more resistant to desiccation than females of S. pictus, showing a higher degree of terrestriality.

Description of the first juvenile stage of Dilocarcinus septemdentatus (Herbst, 1783) (Crustacea, Decapoda, Trichodactylidae)

Abstract A total of 38 freshwater brachyuran species occur in Brazil, of which 79% are distributed in the northern region. However, for only two species of freshwater crabs are descriptions available for their juveniles. The importance of these studies lies in understanding of life-cycle aspects as well the potential elucidation of phylogenetic relationships within the group because the characters are usually solely based on adult specimens. The morphology of the first juvenile stage of the Dilocarcinus septemdentatus (Herbst, 1783) is described and illustrated for the first time based on specimens hatched by an ovigerous female collected in the northeastern region of the Brazilian Amazon. Juveniles of Dilocarcinus pagei Stimpson, 1861 and D. septemdentatus have one flagellar segment on the exopod of the first maxilliped while the only described juvenile of an unidentified species of Trichodactylus Latreille, 1828 has two. Dilocarcinus septemdentatus differs from other congeneric species mainly in the number of setae on the antennae and number of segments of the mandibular palp. Variations in the number of segments and aesthetascs enable the comparison between the juveniles of D. septemdentatus with those of other Brachyuran species previously studied and suggest possible adaptations to freshwater environments.

Manganese tissue accumulation and tyrosine hydroxylase immunostaining response in the Neotropical freshwater crab, Dilocarcinus pagei, exposed to manganese.

Manganese (Mn) is an essential metal for the development and function of the mammalian brain; however, excess Mn accumulation may cause neurological abnormalities resembling Parkinson's disease due to reductions in brain dopamine levels. Because dopamine also regulates many functions in crustaceans, this study examined the effects of Mn accumulation in Dilocarcinus pagei, a Neotropical freshwater crab. Following a 72-h exposure to graded concentrations of MnCl2, Mn accumulation was assessed in several tissues. Glycaemia and the tyrosine hydroxylase (TH) immunostaining response were also examined as indicators of catecholaminergic function and catecholaminergic cell integrity, respectively. Tissue Mn accumulation was variable and occurred in the following order: gills>hepatopancreas>claw muscle>haemolymph. Exposure to 2mM Mn reduced the gill levels of calcium, copper and iron, whereas Mn at all concentrations decreased zinc levels. All Mn-exposed animals showed lower copper levels in the hepatopancreas and haemolymph. Exposure to 2.0mM Mn increased the haemolymph calcium. Mn exposure had no effect on glycaemia, whereas exposure to low Mn concentrations reduced the TH immunostaining response. Analysis of the central nervous system revealed the greatest Mn effect in the cerebral ganglion and the least effect in the abdominal ganglia. These results suggest the operation of an adaptive mechanism for tissue accumulation that could be responsible for the lack of an association between Mn concentrations and metal accumulation. The findings also suggest that Mn, calcium, iron and zinc share a transporter in gill cells and that Mn resistance is greater in the TH-positive cells of this crustacean than in mammalian cells.

Maturidade sexual, lateralidade e dimorfismo sexual do caranguejo dulcícola Dilocarcinus pagei no sudeste do Brasil

This study estimated the sexual maturity of Dilocarcinus pagei Stimpson, 1861 based on relative growth and gonadal development. In addition, a possible sexual dimorphism was reported. The specimens were monthly captured from October 2005 to September 2007 in the Marimbondo/Furnas Hydroelectric Plant Reservoir, municipality of Icem in northwestern Sao Paulo State. Handedness was recorded for males, with the right cheliped propodus invariably longer and wider than the left. The estimated carapace width for morphological sexual maturity in males was 28.7 mm, based on the biometric relationship of the cheliped propodus length vs. carapace width; for females, this value was 24.2 mm, using the relationship of the abdominal width vs. carapace width. The size at gonadal maturity was estimated at 39.2 mm and 39.9 mm, for males and females respectively (CW50). There was not sexual dimorphism in relation to carapace width. For a crab to be able to procreate, it must reach morphological maturity and have developed gonads. Thus a minimum capture size based on the size, at which 50% of the population is considered reproductive, can ensure the continued preservation of this species.

Sexual maturity, handedness and sexual dimorphism of the freshwater crab Dilocarcinus pagei in Southeastern Brazil

This study estimated the sexual maturity of Dilocarcinus pagei Stimpson, 1861 based on relative growth and gonadal development. In addition, a possible sexual dimorphism was reported. The specimens were monthly captured from October 2005 to September 2007 in the Marimbondo/Furnas Hydroelectric Plant Reservoir, municipality of Icem in northwestern São Paulo State. Handedness was recorded for males, with the right cheliped propodus invariably longer and wider than the left. The estimated carapace width for morphological sexual maturity in males was 28.7 mm, based on the biometric relationship of the cheliped propodus length vs. carapace width; for females, this value was 24.2 mm, using the relationship of the abdominal width vs. carapace width. The size at gonadal maturity was estimated at 39.2 mm and 39.9 mm, for males and females respectively (CW50). There was not sexual dimorphism in relation to carapace width. For a crab to be able to procreate, it must reach morphological maturity and have developed gonads. Thus a minimum capture size based on the size, at which 50% of the population is considered reproductive, can ensure the continued preservation of this species.

Population structure, recruitment, and mortality of the freshwater crab Dilocarcinus pagei Stimpson, 1861 (Brachyura, Trichodactylidae) in Southeastern Brazil

Freshwater crabs of the family Trichodactylidae are widely distributed in major river basins of the South American continent. The population structure of one species, Dilocarcinus pagei, was analyzed in an artificial reservoir in Southeastern Brazil, recording data on the sex ratio, recruitment, and mortality. A total of 1339 crabs were collected and included 804 males and 535 females (3 ovigerous and 4 with hatchlings); the sex ratio was 1:0.61 (males: females). Two modes of male and female carapace width (CW) were recorded, with means of 14.4 mm (n = 407) and 38.9 mm (n = 394) for males and 17.9 mm CW (n = 269) and 39.2 mm (n = 267) for females. The mean size of males (CW = 26.6 ± 13.8 mm) was significantly larger than that of females (CW = 28.5 ± 12.8 mm). The data indicated that recruitment occurs in summer (January–March), with the reproductive period in spring (October–December), periods with the highest rainfall and temperature values in the region. Reproduction leads to the death of the parents, influencing the sex ratio, which oscillates mainly during the reproductive period.

Reproductive behaviour of three species of freshwater crabs of the family Trichodactylidae (Crustacea: Decapoda) including forced copulation by males

This report includes a detailed description of the reproductive behaviour of the freshwater crab Zilchiopsis collastinensis in the family Trichodactylidae and some observations on two other genera. It presents observations on the courtship, copulation, spawning, incubation and maternal care in Z. collastinensis. No discernible courtship behaviour occurred. We found instead that forced copulation is practised by males. Z. collastinensis copulations were observed in between April and October, for Dilocarcinus pagei between January and August, and throughout the year for Trichodactylus borellianus. The spawning behaviour of all of the species observed took place out of the water. Incubation lasted between 46 and 62 days in D. pagei, 37 and 41 days in Z. collastinensis and 8 and 12 days in T. borellianus. The number of juveniles carried by each ovigerous female ranged from 651 ± 172 in Z. collastinensis, through 582 ± 8 in D. pagei to 63 ± 33 in T. borellianus. The results support the proposition that members of the family Trichodactylidae, comprising exclusively endemic freshwater crabs, have evolved unusual adaptive reproductive behaviours to optimize their reproductive fitness in unstable environments.

The relative growth and sexual maturity of the freshwater crab Dilocarcinus pagei (Brachyura, Trichodactylidae) in the northwestern region of the state of São Paulo

The aim of the present study was to determine the size at sexual maturity in the freshwater crab Dilocarcinus pagei Stimpson, 1861, from a population located in Mendonça, state of São Paulo, Brazil. The crabs were sampled monthly (July 2005 to June 2007), at Barra Mansa reservoir. The specimens were captured manually or in sieves passed through the aquatic vegetation. The crabs were captured and separated by sex based on morphology of the pleon and on the number of pleopods. The following dimensions were measured: carapace width (CW); carapace length (CL); propodus length (PL); and abdomen width (AW). The morphological analysis of the gonads was used to identify and categorize individuals according to their stage of development. The morphological maturity was estimated based on the analysis of relative growth based on the allometric equation y = ax b. The gonadal maturity was based on the morphology of the gonads by the method CW50 which indicates the size at which 50% of the individuals in the population showed gonads morphologically mature to reproduction. The biometric relationships that best demonstrated the different patterns of growth for the juvenile and adult stages were CW vs. PL for males and CW vs. AW for females (p&lt;0.001). Based on these relationships, the estimated value to morphological sexual maturity was 21.5 mm (CW) in males and 19.7 mm (CW) in females. The determination of the size at sexual maturity and the adjustment of the data based on the logistic curve (CW50) resulted in a size of 38.2 mm for males and 39.4 mm for females (CW). Based on the data obtained for sexual maturity for D. pagei, we can estimate a minimum size for capture of 40 mm (CW). This minimum size allows at least half of the population to reproduce and retains the juveniles and a portion of the adults in the population.

Calcium transport in gill cells of Ucides cordatus, a mangrove crab living in variable salinity environments

Crustaceans show discontinuous growth and have been used as a model system for studying cellular mechanisms of calcium transport, which is the main mineral found in their exoskeleton. Ucides cordatus, a mangrove crab, is naturally exposed to fluctuations in calcium and salinity. To study calcium transport in this species during isosmotic conditions, dissociated gill cells were marked with fluo-3 and intracellular Ca2+ change was followed by adding extracellular Ca2+ as CaCl2 (0, 0.1, 0.25, 0.50, 1.0 and 5mM), together with different inhibitors. For control gill cells, Ca2+ transport followed Michaelis–Menten kinetics with Vmax=0.137±0.001 ∆Ca2+i (μM×22.104cells−1×180s−1; N=4; r2=0.99); Km=0.989±0.027mM. The use of different inhibitors for gill cells showed that amiloride (Na+/Ca2+ exchange inhibitor) inhibited 80% of Ca2+ transport in gill cells (Vmax). KB-R, an inhibitor of Ca influx in vertebrates, similarly caused a decrease in Ca2+ transport and verapamil (Ca2+ channel inhibitor) had no effect on Ca2+ transport, while nifedipine (another Ca2+ channel inhibitor) caused a 20% decrease in Ca2+ affinity compared to control values. Ouabain, on the other hand, caused no change in Ca2+ transport, while vanadate increased the concentration of intracellular calcium through inhibition of Ca2+ efflux probably through the plasma membrane Ca2+-ATPase. Results show that transport kinetics for Ca2+ in these crabs under isosmotic conditions is lower compared to a hyper-regulator freshwater crab Dilocarcinus pagei studied earlier using fluorescent Ca2+ probes. These kinds of studies will help understanding the comparative mechanisms underlying the evolution of Ca transport in crabs living in different environments.