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Increased salinity affects survival and osmotic response of rusty crayfish Orconectes rusticus Girard, 1852 and northern clearwater crayfish O. propinquus Girard, 1852 (Decapoda: Astacoidea: Cambaridae) as salinity increases: the potential for estuarine invasions
Abstract and Figures
The potential colonization of the rusty crayfish, Orconectes rusticus (Girard, 1852), has previously focused on lakes and streams of northeastern United States and southeastern Canada, but estuaries have not been considered. Rusty crayfish have recently been reported in tributaries of the Chesapeake Bay and the potential exists for crayfishes to invade and spread into the estuary. We determined survival, hemolymph osmotic pressure, and identified possible mechanisms of osmoregulation of the invasive O. rusticus and northern clearwater crayfish, Orconectes propinquus (Girard, 1852), in salinities of 0.5, 5, 15, and 30 ppt. Survival of both crayfishes (>83%) was unaffected at salinities of up to 15 ppt but declined significantly at 30 ppt to 17% for O. rusticus ( P < 0 . 05 ) and 50% for O. propinquus ( P > 0 . 05 ). Hemolymph osmotic pressure in both species was higher than the external medium up to 15 ppt, and then became nearly isosmotic with salinities at 30 ppt with a significant species by treatment interaction ( F 3 , 55 = 4 . 4627 , P = 0 . 0071 ). The primary osmoregulatory mechanisms in crayfishes involve ions (Na+ and Cl−) and free amino acids (FAAs) in muscle tissues. Concentrations of Na+ and Cl− increased with increasing salinity in both species and accounted for 74-91% of the total hemolymph osmotic pressure with a significant species (Pillai’s Trace = 0.9565, P < 0 . 0001 ) and treatment effect (Pillai’s Trace = 0.23189, P < 0 . 0001 ). FAA concentrations in hemolymph remained low (1-4 mM) and did not differ significantly with increased salinity ( P > 0 . 05 ). FAA in tail muscle tissue increased significantly with increasing salinity with a significant species by treatment interaction ( F 3 , 20 = 5 . 1911 , P = 0 . 0082 ). Both O. rusticus and O. propinquus were active in salinities of up to 15 ppt and were able to osmoregulate. Based on these laboratory experiments, the potential exists for both of these species to spread through large areas of estuaries into new rivers potentially threatening previously isolated watersheds.
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... Another possible explanation for the observed discrepancies could be that crayfish in general, and non-native species in particular, are responding to variation in environmental factors Magoulick 2007, Jackson et al. 2017). Like many aquatic organisms, crayfish are subject to factors such as current velocity (Clark et al. 2008, Perry andJones 2018), temperature (Gherardi et al. 2013, Johnson et al. 2014, Stoffels et al. 2016, substrate type (Adams and Marks 2016) and salinity (Bazer et al. 2016), among others. These factors all have the potential to affect crayfish physiology, behavior and performance (Dunson and Travis 1991), and this can have consequences for the ecological roles that crayfish play (Wellnitz and Poff 2001). ...
Non-native crayfish can have impacts on stream communities that are highly variable. A possible explanation for this variability is that crayfish are responding in a context-dependent manner to variation in environmental factors. Among the most critical environmental factors in streams is current velocity. Moving water defines lotic ecosystems and many benthic organisms, including crayfish, respond to its influence. To examine how current velocity affected the impacts of non-native Orconectes rusticus crayfish on benthic communities, we conducted a cage-enclosure experiment in a Wisconsin stream. We hypothesized that current velocities > 50 cm s⁻¹ would decrease the effects that O. rusticus had on community composition (macroinvertebrate richness and numbers) and physical structure (sediment accumulation). Three cage enclosure treatments (open, closed crayfish and closed control) were grouped into eight replicate blocks divided equally among streambed regions of slow (< 50 cm s⁻¹) and fast (> 50 cm s⁻¹) current. Open cages allowed resident crayfish access, closed crayfish cages contained one O. rusticus, and closed controls had no crayfish. After three weeks, crayfish cages had lower macroinvertebrate abundance and richness and less sediment accumulation. Current velocity showed a positive relationship to macroinvertebrates in general, and a negative relationship to sediment build-up. The most common macroinvertebrates were hydropsychid caddisflies that responded to O. rusticus in a context-dependent manner such that cages containing crayfish had decreased hydropsychid numbers in fast current, but not in slow. Open cage treatments showed a similar pattern, suggesting that natural crayfish densities in the stream were also sufficient for lowering hydropsychid numbers in fast current. Our study demonstrates that current velocity may provide an important context for understanding the effects that O. rusticus have on benthic communities, not just in terms of what these crayfish do, but how the benthic communities respond to their presence.
This datasheet on Faxonius rusticus covers Identity, Overview, Distribution, Dispersal, Diagnosis, Biology & Ecology, Environmental Requirements, Natural Enemies, Impacts, Uses, Prevention/Control, Further Information.
The concept of native range in invasion biology is difficult to define since, in many cases, this type of range is unknown and cannot be determined. We investigate the uncertainties related to this concept by focusing on the distribution of Faxonius rusticus (Girard, 1852), also known as the rusty crayfish, which is perceived as possibly the worst invasive crayfish species in North America. In this study, we undertake a comprehensive literature review, which includes 430 studies published between 1852 and 2018, in order to analyze the native and introduced ranges of this species. The rusty crayfish was reported to occur in 33 states in the U.S.A. and 3 Canadian Provinces. Ten of these U.S. states and one Canadian Province have been included multiple times in both the native and the non-native ranges of this crayfish. The confusion regarding the limits and history of the native range of the rusty crayfish has implications for the conservation of this species in various jurisdictions. This review also demonstrates that even for intensely studied species perceived as invasive, we often do not have a clear understanding of essential concepts such as native and non-native range.
The Australian redclaw crayfish Cherax quadricarinatus is a freshwater crustacean aquacultured in many countries. Redclaw crayfish are often exposed to saline waters in attempts to improve flavor, to relieve stress during transport, and to prevent or treat parasitic infestations. However, the effect of salinity on the crayfish osmoregulatory process is not well studied. In the present work, we assessed the effect of various salinities on survival, growth, and osmoregulation in redclaw crayfish. Adult crayfish were maintained at seven salinities (0, 2, 4, 6, 8, 10, and 12 ppt) for 4 weeks, and hemolymph osmolality, gill sodium potassium ATPase activity, and sodium potassium chloride cotransporter expression were assessed. In another experiment, juvenile crayfish were size sorted to similar weights and stocked at four salinities (0, 2, 4, and 6 ppt) for 8 weeks. The animals were group weighed every 2 weeks and individually weighed at the end of the eighth week. Hemolymph osmolality was constant as salinity increased from 0 to 10 ppt then a significant increase was observed at 12 ppt. Redclaw growth rate decreased with an increase in salinity from 0 to 6 ppt. Sodium potassium ATPase activity and sodium potassium chloride cotransporter expression increased with salinity increase. Although salinity might help treat ectoparasites, improve taste, and reduce transportation stress, long‐term exposure increases osmoregulatory metabolic costs and affects growth and energy consumption.
Haemolymph iono-and osmoregulation and acid-base balance were re-corded after 48 h exposure at 15 °C to a range of increasing ambient salinities (0, 25, 50 and 75% sea water) in the euryhaline crayfish Pacifastacus leniusculus (Dana). Except for K+, concentrations of all measured inorganic ions and osmolality were significantly elevated in 50 and 75 % SW. When compared with ambient changes there was evidence of a transition from hyper-to hypoionic regulation above 44% SW. Ca 2+ was regulated for a constant blood-medium difference. A progressive reduction in total CO 2 was recorded; pH was maintained except in 75 % SW where a haemolymph acidosis developed. To permit calculation of CO 2 tension (P COl), carbon dioxide solubility coefficient (aco 8) an(^ t n e apparent first dissociation constant of carbonic acid (p^i) were experimentally determined in vitro. OL COt decreased progressively with acclimation salinity but was unaffected by circulating pro-tein. pK[ decreased as a function both of physiological pH and increasing haemolymph ionic strength. P C o,> calculated using these empirical constants, progressively decreased with high-salinity acclimation. The resulting * hypo-capnic alkalosis' was partially offset by a metabolic acidosis, whose correlation with extracellular anisosmotic and intracellular isosmotic regulation is discussed.
Cascading trophic interactions are important in many freshwater pelagic food webs, but their importance in more complex, omnivore-rich littoral-zone food webs is less well known. We tested the existence of a trophic cascade involving omnivorous crayfish (Orconectes rusticus), macroinvertebrates, periphyton, and macrophytes using 9-m^2 cages in the littoral zone of Plum Lake, Wisconsin, USA. Treatments in the replicated (N = 4) experiment were crayfish enclosures, crayfish exclosures, and cageless references. During June-September, we measured macrophyte shoot numbers, macroinvertebrate numbers, and periphyton (on plastic strips) chlorophyll a, and dry mass (DM). We expected that crayfish foraging would directly reduce abundance and change species composition of macrophytes and macroinvertebrates and would indirectly enhance periphyton abundance by reducing the abundance of grazing snails. In enclosures, macrophyte and snail (but not nonsnail macroinvertebrate) densities declined significantly throughout the experiment, whereas densities of macrophytes, snails, and nonsnail macroinvertebrates increased in exclosures and cageless references. Some of the reduction in macrophytes resulted from nonconsumptive fragmentation of macrophytes by crayfish. Consistent with the cascading trophic interactions model, periphyton chlorophyll a per unit surface area increased in enclosures, but declined in exclosures. Periphyton quality (as indexed by chlorophyll a/DM) also increased in enclosures relative to exclosures and cageless references. However, because of large reductions in macrophyte surface area (which periphyton colonizes) in enclosures, total amount of periphyton chlorophyll a in enclosures (relative to exclosures) probably declined while periphyton quality per unit surface area and periphyton quality increased. Thus, the impacts of crayfish omnivory on periphyton, expressed in two conflicting indirect effects, confirm the possibility that omnivory can complicate cascading trophic predictions. Overall, results support the existence of strong trophic interactions in the littoral zone, in which omnivorous crayfish control abundance of macrophytes, snails, and periphyton.
Rusty crayfish (Orconectes rusticus) were first observed in Trout Lake, Wisconsin, in 1979 and took 19 years to completely disperse around the littoral zone, advancing at an average rate of 0.68 km(.)year(-1). With the invasion of rusty crayfish, we found that fishes that share prey taxa with crayfish declined in numbers over time, but piscivorous fish species did not change in abundance. Snails declined from >10 000 to <5 snails(.)m(-2) in one of the first invaded areas. Mean abundance of Odonata, Amphipoda, and Trichoptera decreased significantly lake-wide. Resident crayfish species nearly disappeared, although total crayfish abundance, driven by high abundances of rusty crayfish, continued to rise. Submerged macrophyte species richness declined by as much as 80% at some locations. Together these responses demonstrate dramatic long-term changes in the littoral zone biota of Trout Lake. Continued invasions of similar lakes in the region suggest that these impacts are occurring on a region-wide basis with potentially irreversible effects on communities and ecosystems. Only through long-term natural experiments such as this study can researchers ascertain the full extent of invasions and their impacts on community and ecosystem process that respond at spatial and temporal scales not captured in mesocosm studies.
North America harbors about 390 native species of crayfishes, 75% of the world's total. In this arti- cle, we highlight the threats posed by nonindigenous crayfishes to freshwater ecosystem function, fisheries, and the biodiversity of native crayfishes; draw some lessons for North American freshwa- ter conservation from the experience with nonindigenous crayfishes in Europe; and review existing regulations that address the introduction of nonindigenous crayfishes. Most North American cray- fishes have naturally small ranges in the southeastern United States, rendering them very vulnera- ble to environmental change. In contrast, Europe has only five, broadly distributed, native crayfish- es, all of which have been greatly affected by environmental changes, especially the introduction of nonindigenous crayfishes (mostly from North America). In response, many European governments have adopted strict regulations to protect native crayfishes. The loss of thousands of populations of native European crayfishes and the political responses to it offer useful guidance to efforts to pro- tect North American freshwater biodiversity and ecosystems. As in Europe, the most important threat to native North American crayfish biodiversity is nonindigenous crayfishes (many from with- in North America). In several well-documented cases, nonindigenous crayfishes have greatly altered North American lake and stream ecosystems, harmed fisheries, extirpated many popula- tions of native crayfishes, and contributed to the global extinction of at least one native crayfish species. However, most species are still relatively unaffected, but the smaller ranges of most North American crayfishes make them more vulnerable than European crayfishes. Thus, a narrow win- dow of opportunity exists to protect the function of North American aquatic ecosystems, their fish- eries, and the unique biodiversity of crayfishes that they contain.
SYNOPSIS. The physiological mechanisms by which aquatic animals regulate the osmoconcentration of their body fluids remain unclear despite many excellent stud- ies of tissue and cell function. This review summarizes the current status of an ongoing molecular biological approach to investigating transporters and transport- related enzymes in ion-transporting gills of osmoregulating crustaceans. We have identified cDNAs coding for six candidate proteins in gills of the blue crab Calli- nectes sapidus and the green shore crab Carcinus maenas, including a Na 1 1 K 1 - ATPase a-subunit, a V-type H 1 -ATPase B-subunit, a Na 1 /H 1 exchanger, a Na 1 / K 1 /2Cl 2 cotransporter, two isoforms of carbonic anhydrase, and arginine kinase. Although our account is far from complete, examination of mRNA abundance by quantitative reverse transcription/polymerase chain reaction (RT/PCR) has iden- tified candidates that are preferentially expressed in gill epithelium, including the Na 1 1 K 1 -ATPase a-subunit and Na 1 /H 1 exchanger. The osmoregulatory response to salinity reduction includes enhanced mRNA expression of at least one form of carbonic anhydrase.
Arthropod generalist predators (AGP) are widespread and abundant in both aquatic and terrestrial ecosystems. They feed upon herbivores, detritivores, and predators, and also on plant material and detritus. In turn, AGP serve as prey for larger predators. Several prominent AGP have become invasive when moved by humans beyond their native range. With complex trophic roles, AGP have diverse effects on other species in their introduced ranges. The invaders displace similar native species, primarily through competition, intraguild predation, transmission of disease, and escape from predation and/or parasites. Invasive AGP often reach higher densities and/or biomass than the native predators they replace, sometimes strengthening herbivore regulation when invasive AGP feed on key herbivores, but sometimes weakening herbivore suppression when they eat key predators. The complexity and unpredictability of ecological effects of invasive AGP underscores the high risk of adverse consequences of intentional in...
Adult male crayfish, Cherax quadricarinatus, were exposed to the salinities of 0 (control), 7.5, 15, 25 and 35 g L−1 for 3 weeks. Survival, oxygen consumption rate, hemolymphatic levels of glucose, lactate, sodium, potassium, pH, and free amino acids (FAA), as well as FAA concentration in muscle, were determined. Survival was significantly reduced (p < 0.05) only at the highest salinity assayed, together with a significant (p < 0.05) increase of glucose and decrease of lactate. Concerning ions, a hyper-regulation of both hemolymphatic sodium and potassium was maintained up to a salinity of 15 g L−1, at which hemolymph became isoionic with ambient water. A certain degree of ionic hypo-regulation was also noted. Hemolymph pH levels decreased as salinity increased from 0 to 15 g L−1. FAA content in muscle showed an increase parallel to that of hemolymphatic sodium, in accordance with their expected function in the isosmotic regulation of muscular cells.
Over 45 years have passed since the last examination of Maryland's crayfish fauna. We compiled crayfish records from over 1400 sites sampled since 1989 and present an update on the current status and distribution of Maryland's 9 native species. Five non-native species have become established in Maryland waters and represent the greatest threat to Maryland's native species. Orconectes virilis (Virile Crayfish), the most widespread invasive species in the state, has been primarily introduced by anglers as bait and has rapidly expanded its distribution in central Maryland. The spread of this species has been followed by concurrent declines in native species including O. limosus (Spinycheek Crayfish) and O. obscurus (Allegheny Crayfish). Non-native Cambarus thomai (Little Brown Mudbug), O. rusticus (Rusty Crayfish), Procambarus clarkii (Red Swamp Crawfish), and P. zonangulus (Southern White River Crawfish) are now established in Maryland as a result of aquaculture and bait introductions. Recent taxonomic revisions have also added C. carinirostris (Rock Crawfish) to the list of species present in the state.
This study presents a methodology for combining archival data storage tags (DSTs) and ultrasonic transmitters to investigate the microhabitat conditions of adult Cancer magister (Dana), inhabiting an estuary. The temperature, salinity and depth experienced by free-ranging Dungeness crabs were recorded at 10-min intervals for periods ranging from 1 week to 8 months. Crabs were tracked using a hydrophone, and tags were recovered via concentrated trapping or returned by recreational fishers for a reward. These methods led to a return rate of 50%. Representative CTD tag data showed that the conditions recorded at fixed stations within the estuary were not reflective of those experienced by free-ranging crabs, but rather crabs were able to orientate and avoid low salinity within the estuary. The prevalence of low salinity exposure was linked to times of increased food availability within the estuary, suggesting that crabs were entering the shallows of the estuary to forage. The techniques used in this study demonstrate that DSTs are a viable means of determining the microhabitat conditions of crustaceans inhabiting highly variable environments.
The freshwater crayfishes are distributed across all but the Indian and Antarctic continents with centers of diversity in
the southeastern Appalachian Mountains in the Northern Hemisphere and in south-east Australia in the Southern Hemisphere.
There are currently over 640 described species of freshwater crayfishes with an average of 5–10 species still being described
each year. Freshwater crayfishes can serve as keystone species in aquatic habitats, but a few species are also significantly
invasive and can cause impressive damage to the fragile freshwater habitat. Crayfishes inhabit caves, burrows, streams, lakes
and strong burrowers can even be found in terrestrial habitats where they have burrowed to the water table or where rainfall
is sufficiently abundant to provide the needed moisture. The freshwater crayfishes, like the habitats in which they are encountered,
are generally endangered to some degree and conservation efforts would do well to focus on them as key elements of the freshwater
ecosystem.
Organic osmolytes are small solutes used by cells of numerous water-stressed organisms and tissues to maintain cell volume. All known osmolytes are amino acids and derivatives, polyols and sugars, methylamines, and urea; unlike salt ions, most are “compatible,” i.e. , do not perturb macromolecules. In addition, some stabilize macromolecules and are “counteracting” towards perturbants, e.g. , methylamines can stabilize proteins and ligand binding against perturbations by urea in elasmobranchs and mammalian kidney, and (our latest findings) high hydrostatic pressure in deep-sea animals. Methylamines appear to coordinate water molecules tightly, resulting in osmolyte exclusion from hydration layers of peptide backbones. This makes unfolded protein conformations entropically unfavorable (work of Timasheff, Galinski, Bolen and coworkers). These properties have led to proposed uses in biotechnology, agriculture and medicine, including improved biochemical methods, in vitro rescue of misfolded proteins in cystic fibrosis and prion diseases (work of Welch and others), and plants engineered for drought and salt tolerance. These properties also explain some but not all of the considerable variation in osmolyte composition among species with different metabolisms and habitats, and among and within mammalian tissues in development.
Osmoregulation was studied during the postembryonic development of Astacus leptodactylus Eschscholtz 1823 in juvenile stages 1-8 and in adults. Juveniles hatch and later stages develop in freshwater or in moderately saline waters. The time of acclimation from freshwater to a saline medium increased from early juveniles to adults. At all stages, it was longer than in comparable stages of marine crustaceans, reflecting the high impermeability of the teguments to water and ions. All stages were able to hyperisoosmoregulate. In freshwater, the ability to hyperosmoregulate was established at hatching and increased during development. The hemolymph osmolality increased from 286 mosm kg-1 in stage 1 juveniles to 419 mosm kg-1 in adults. All stages also hyperregulated at low salinities (7 per thousand and 13 per thousand salinity) and were osmoconformers at higher salinities up to 21 per thousand salinity. The lowest isosmotic salinity tended to increase with the developmental stages. The ability to osmoregulate at hatch and throughout postembryonic development is probably a key physiological adaptation in this and other freshwater crayfish.
Adaptations to salinity are reviewed throughout development in both species of the genus Homarus. Some populations of homarid lobsters are known to inhabit coastal and estuarine areas where salinity fluctuates. Salinity tolerance varies during development, with 50 % lethal salinities (LS(50)) ranging from approximately 15-17 in larvae to approximately 12 in postlarvae and 10 in adults. Larval and adult lobsters can avoid low-salinity areas using behavioural strategies. When exposed to low salinity, the capacity to osmoregulate varies with development. Embryos are osmoconformers and are osmotically protected by the egg membranes. Larvae are also osmoconformers, and the pattern of osmoregulation changes at metamorphosis to hyper-regulation, which is retained throughout the later stages up to the adult stage. Exposure to low salinity increases the activity of Na(+)/K(+)-ATPase in postlarvae and later stages. The level of osmoregulation evaluated through the osmoregulatory capacity (the difference between haemolymph and medium osmolalities) is negatively affected by low temperature (2 degrees C). The variations in haemolymph osmolality resulting from osmoconforming or partial osmoregulation are compensated by intracellular iso-osmotic regulation. Neuroendocrine control of osmoregulation appears in postlarvae and seems to involve the crustacean hyperglycaemic hormone. In adult lobsters, the gills appear to have a respiratory function only, and extracellular osmoregulation is effected by the epipodites, with the addition of the branchiostegites at low salinity. These organs are present at hatching. Transmission electron microscopy and immunolocalization of Na(+)/K(+)-ATPase reveal that the epipodites become functional in larvae and that the branchiostegites become functional in postlarvae. An integrated series of events links the appearance of osmoregulatory tissues, the increase in Na(+)/K(+)-ATPase activity, the occurrence in postlarvae of hyper-regulation at low salinity and the increase in salinity tolerance. Further ecological and physiological studies are proposed for a better understanding of the adaptive significance of the ontogeny of osmoregulation in lobsters.
Despite their widespread use as model organisms, the phylogenetic status of the around 520 species of freshwater crayfish is still in doubt. One hypothesis suggests two distinct origins of freshwater crayfish as indicated by their geographical distribution, with two centres of origin near the two present centres of diversity; one in south-eastern United States and the other in Victoria, Australia. An alternative theory proposes a single (monophyletic) origin of freshwater crayfish. Here we use over 3000 nucleotides from three different gene regions in estimating phylogenetic relationships among freshwater crayfish and related Crustacea. We show clear evidence for monophyly of freshwater crayfish and for the sister-group relationship between crayfish and clawed lobsters. Monophyly of the superfamilies Astacoidea and Parastacoidea is also supported. However, the monophyly of the family Cambaridae is questioned with the genus Cambaroides being associated with the Astacidae.
The present investigation examined the microanatomy and mRNA expression and activity of ion-motive ATPases, in anterior and posterior gills of a South American, true freshwater crab, Dilocarcinus pagei. Like diadromous crabs, the anterior gills of this hololimnetic trichodactylid exhibit a highly attenuated (2-5 microm), symmetrical epithelium on both lamellar surfaces. In sharp contrast, the posterior gill lamellar epithelia are markedly asymmetrical. Their proximal side consists of thick (18-20 microm) cells, displaying features typical of a transporting epithelium, while the distal epithelium is thin (3-10 microm) and formed entirely by apical pillar cell flanges. Both anterior and posterior gills express Na+/K+- and V-ATPases. Phylogenetic analysis of partial cDNA sequences for the Na+/K+-ATPase alpha-subunit and V-ATPase B-subunit among various crab species confirmed the previous classification and grouping of D. pagei based on morphological criteria. Semi-quantitative RT-PCR clearly showed that mRNA for both ion pump subunits is more intensely expressed in posterior gills. Na+/K+-ATPase activity in the posterior gills was nearly fourfold that of anterior gills, while V-ATPase and F-ATPase activities did not differ. A negative short-circuit current (Isc) was measured using the distal side of split, posterior gill lamellae, mounted in a modified Ussing chamber and perfused symmetrically with identical hemolymph-like salines. Although hemolymph-side ouabain did not affect this current, concanamycin significantly reduced Isc without altering preparation conductance, suggesting V-ATPase-driven Cl- absorption on the distal side of the posterior gill lamellae, as known to occur in diadromous crabs adapted to freshwater. These findings suggest that active Na+ uptake predominates across the thick proximal epithelium, and Cl- uptake across the thin, distal epithelium of the posterior gill lamellae.
During artificial seawater acclimation in the laboratory of freshwater Japanese mitten crab Eriocheir japonicus, glycine and L-proline other than D- and L-alanine increased significantly in the muscle of the immature group, while no significant increase in glycine and L-proline was found in the mature group. Total inorganic ions in the muscle of the mature crabs increased significantly along with the salinity increments and reached the levels of estuarine specimens captured during downstream migration. In the immature group, inorganic ions also increased during salinity stress but the increase was far lower than those in the mature group. These data suggest that immature crabs cannot tolerate high ionic concentrations in muscle and have to increase glycine and L-proline during seawater acclimation. After adjustment of salinity tolerance, mature crabs incorporate inorganic ions in muscle and their cell volumes are likely regulated mainly by D- and L-alanine and inorganic ions.
Hemolymph ion concentrations and osmolalities increased largely during seawater acclimation for both immature and mature crabs and reached the same levels as those for estuarine and sea specimens in the natural environment. These data suggest that no special adjustment of hemolymph osmoregulatory capability occurs along with the maturation.
This chapter on osmoregulation of aquatic arthropods deals mainly with crustaceans. Among the Pancrustacea group, the Hexapoda (formerly insects) will be discussed in Chapter 7. Section VIII of this chapter is devoted to a few other aquatic arthropods. Osmotic and ionic regulations have been studied in crustaceans for over 80 years and have been reviewed in Robertson, Potts and Parry, Shaw, Lockwood, Prosser, Mantel and Farmer, Schoffeniels and Dandrifosse, Péqueux, and Péqueux et al. In this chapter, we briefly summarize the knowledge on crustacean osmoregulation up to the 1980s and 1990s, before concentrating on more recent information in two areas. One is linked to the adaptive function of osmoregulation—that is, the relations between osmoregulation and the ecology of crustaceans, especially during their development. The second deals with the mechanisms of osmoregulation, mainly at the cellular and molecular levels.
The physiological mechanisms by which aquatic animals regulate the osmoconcentration of their body fluids remain unclear despite many excellent studies of tissue and cell function. This review summarizes the current status of an ongoing molecular biological approach to investigating transporters and transport-related enzymes in ion-transporting gills of osmoregulating crustaceans. We have identified cDNAs coding for six candidate proteins in gills of the blue crab Callinectes sapidus and the green shore crab Carcinus maenas, including a Na+ + K+-ATPase α-subunit, a V-type H+-ATPase B-subunit, a Na+/H+ exchanger, a Na+/K+/2Cl− cotransporter, two isoforms of carbonic anhydrase, and arginine kinase. Although our account is far from complete, examination of mRNA abundance by quantitative reverse transcription/polymerase chain reaction (RT/PCR) has identified candidates that are preferentially expressed in gill epithelium, including the Na+ + K+-ATPase α-subunit and Na+/H+ exchanger. The osmoregulatory response to salinity reduction includes enhanced mRNA expression of at least one form of carbonic anhydrase.
Organic osmolytes are small solutes used by cells of numerous water-stressed organisms and tissues to maintain cell volume. All known osmolytes are amino acids and derivatives, polyols and sugars, methylamines, and urea; unlike salt ions, most are “compatible,” i.e., do not perturb macromolecules. In addition, some stabilize macromolecules and are “counteracting” towards perturbants, e.g., methylamines can stabilize proteins and ligand binding against perturbations by urea in elasmobranchs and mammalian kidney, and (our latest findings) high hydrostatic pressure in deep-sea animals. Methylamines appear to coordinate water molecules tightly, resulting in osmolyte exclusion from hydration layers of peptide backbones. This makes unfolded protein conformations entropically unfavorable (work of Timasheff, Galinski, Bolen and coworkers). These properties have led to proposed uses in biotechnology, agriculture and medicine, including improved biochemical methods, in vitro rescue of misfolded proteins in cystic fibrosis and prion diseases (work of Welch and others), and plants engineered for drought and salt tolerance. These properties also explain some but not all of the considerable variation in osmolyte composition among species with different metabolisms and habitats, and among and within mammalian tissues in development.
Osmoregulation and salinity tolerance were studied in larvae and post-larvae of two species of crustaceans, Homarus americanus and Penaeus japonicus, that have different types of embryonic development. In both species, salinity tolerance decreased through the larval stages, was at a minimum at metamorphosis, and increased in post-larval stages. In H. americanus, the lethal salinity for 50% of the animals (24 h LS50) at 20°C was about 17‰ at metamorphosis, and about 10.5-12‰ in stages IV and V. In P. japonicus, the 24 h LS50 at 25°C was about 25‰ at metamorphosis, and about 7-10‰ from the sixth post-larval stage onwards. In both species, larvae were hyper-osmoconformers and the osmoregulatory pattern changed after metamorphosis to the juvenile/adult type. In H. americanus, stages IV and V slightly hyper-osmoregulated in low salinities. In P. japonicus, post-larvae hyper-hypo-regulated, and their regulatory capacity increased up to the fifth post-larval stage. In young stages of H. americanus and P. japonicus, osmoregulation and salinity tolerance appear correlated, and are modified at metamorphosis. These results are discussed with regard to their ecological and physiological implications and to previous studies on other species.
It is predicted that two species of crayfish (Astacus leptodactylusandPacifastacus leniusculus) introduced into Britain and now widely spread in the wild may colonize the estuarine environment as they have done within their home ranges. The only crayfish native to British waters,Austropotamobius pallipes, is not known from the estuarine environment. Adults of all three species were found to have a similar osmotic response when transferred to a range of seawater concentrations (salinities of 7, 14, 21 and 28 where 100% seawater equals 35) for 48-h periods. The osmolality of the haemolymph increased significantly as the salinity increased. All three species hyper-regulated in freshwater and low salinities (7 and 14), and hyporegulated in high salinities (21 and 28). The transition from hyper- to hyporegulation was found to be: 497 mOsm kg−1—A. pallipes, 470 mOsm kg−1—A. leptodactylusand 523 mOsm kg−1—P. leniusculus. BothA. leptodactylusandP. leniusculushyper-regulated over a 6-week period in freshwater and salinities of 7 and 14. In reverse transfer experiments, no mortalities occurred in either species when they were transferred directly back to freshwater after having been exposed to salinities of 7, 14 and 21 for a 9-week period.
The freshwater crayfish, Procambarus clarkii, is a strong hyperosmoregulator in fresh water (FW) and 25% sea water (25% SW), and it weakly hyperosmoregulates in 50 and 75% SW. Procambarus clarkii produces a dilute urine in FW and 25% SW, but the urine becomes progressively more concentrated in 50% SW and is nearly isosmotic with the haemolymph in 75% SW. Antennal gland Na,K-ATPase ESA was highest in crayfish acclimated in FW and decreased significantly in animals acclimated for two weeks or two months in 50 and 75% SW. It is hypothesized: (a) that only a portion of the antennal gland Na,K-ATPase powers renal salt reabsorption and, thus, the production of dilute urine in P. clarkii, and (b) that P. clarkii may maintain high “basal” levels of antennal gland Na,K-ATPase to power other, non-osmoregulatory transport functions such as organic acid secretion into the urine and sugar and amino acid reabsorption from it. The time course of decreased antennal gland ESA after abrupt transfer of crayfish from FW to 50% SW is consistent with enzyme degradation.
Analyses have been made, with respect to the principal inorganic constituents, of the blood and urine of Carcinus, when living in normal sea water, diluted sea water, and sea water modified by the addition of magnesium sulphate. The composition of the blood of individuals living in normal sea water is as follows (the concentration of each ion being expressed as a percentage of the concentration that would be expected if the blood were in dialysis equilibrium with the external medium): Na 110%, K 118%, Ca 108%, Mg 34%, Cl 104%, SO4 61%. This ionic regulation is the resultant of the following processes: active absorption by the gills of sodium, potassium, calcium and chloride at a rate greater than that at which they are lost by diffusion; differential excretion by the antennary gland, which tends to conserve potassium and eliminate magnesium and sulphate; inward diffusion across the gills of magnesium and sulphate in accordance with the concentration gradient. In normal conditions there is active absorption of water. In dilute media, when osmoregulation begins, this is suspended, and possibly there is a fall in the passive permeability of the gills to water. In other respects osmoregulation is brought about by an intensification of the processes responsible for ionic regulation. The permeability of the cuticle under physiological conditions is such that it does not affect the salt and water exchange of the animal, which is controlled by the branchial epithelium. The structure of the gills of four species of Decapoda is described, and correlated with their powers of osmotic and ionic regulation.
Lobsters took 72 hr to adapt to a salinity of 20‰, with urine becoming markedly hypoosmotic to the blood during the first 25 hr, then increasing in concentration over the next 48 hr, though remaining significantly hypoosmotic to the blood. Adaptation to a salinity of 37‰ took 24 hr: the urine became almost isosmotic with the blood: the gastric and rectal fluids became hyperosmotic to the blood. Blood freezing-point determinations showed that over the salinity range 20–37‰ the lobster is able to osmoregulate to a limited extent only towards the lower end of the range, being otherwise an "osmocon-former." Salt-loading experiments indicated that the excess salts were rapidly excreted into the gut. It is concluded that the antennal glands are at least partly responsible for elimination of excess water, but that the gut is the site of salt excretion, and that there is rapid adjustment of salt imbalance.
Des 20 espèces incluses par Girard (1852) dans son travail: "A revision of the North American Astaci with observations on their habits and geographical distribution", deux seulement, Cambarus carolinus Erichson et C. robustus Girard, sont reconnues dans la combinaison même employée par Girard. Six ont été placées en synonymie (C. affinis et C. pealei = Orconectes limosus; C. montanus et C. pusillus = C. bartonii; et C. fossor et C. nebrascensis = C. d. diogenes). Les douze qui restent sont traitées comme suit: O. pellucidus, Pacilastacus leniusculus (pour C. oreganus), O. r. rusticus, O. p. pellucidus, C. b. bartonii, C. l. longulus, P. g. gambelli, C. d. diogenes, Procambarus blandingii, P. clarkii, P. a. acatus, P. acutissimus.
Marine invertebrates transport amino acids and other organic solutes across their body surfaces. This surface absorption, in some instances, may contribute significantly to the overall nutritional requirements for an organism. Amino acids are accumulated against gradients as high as 106:1 to 107:1 (intracellular:extracellular concentration). The transport mechanism that has been consistently observed to account for this process is Na dependent cotransport. A review of the general characteristics of these transport systems characterized in marine invertebrate epithelia indicates certain common features: Na dependency with coupling coefficients of 2:1 or 3:1 (Na:amino acid translocated), influx coupled to membrane potential, and low intracellular Na activity. Under these conditions Na cotransport can readily account for gradients approaching 107:1. These transport systems may play a role in acquisition of nutrients by marine invertebrates, but it has also been suggested that they may play additional roles in osmoregulation, nutrient conservation, and chemo-reception. © 1993 Wiley-Liss, Inc.
The presence of the yabbie Cherax destructor in a number of wild aquatic systems in the Pilbara and Southwest Coast Drainage Divisions of Western Australia is documented. This is of great concern as all native freshwater crayfishes in Western Australia are endemic and restricted to the southwest, while the Pilbara Division has no native species. An introduced population of C. destructor was sampled monthly from the Hutt River (Pilbara Drainage Division) for determination of life-history and reproductive biology in a wild aquatic system in Western Australia for the first time. Proliferation in that system was attributed to specific traits including: attaining first maturity at the end of its first year of life; a protracted spawning period (July–January); relatively high mean ovarian fecundity of 210.2 (9.24 S.E.); and a rapid growth rate (curvature parameter K=0.78 and asymptotic orbital carapace length OCL∞=51.25mm ascertained from a seasonal von Bertalanffy growth curve) that was comparable to the larger sympatric marron Cherax cainii in this system. The life-history characteristics of C. destructor in the Hutt River were typical of many other invasive crayfish species and it has the potential to impact the unique aquatic ecosystems and the endemic freshwater crayfish species of the region.
The introduction of some crustacean species has produced alterations of freshwater environments and declines of native species
worldwide. The red swamp crayfish, Procambarus clarkii Girard, was introduced in the Southwest Iberian Peninsula in the 1970’s, producing severe impacts on rice agriculture and
on native biota such as macrophytes, gastropods, native crayfish and amphibians. We studied the distribution of P. clarkii in two areas of SW Iberian Peninsula: the Sado River basin (SW Portugal), an area colonized by this species around 1990,
and the Parque Natural del Entorno de Doñana (SW Spain), colonized soon after its introduction in the Iberian Peninsula, in
the 1970’s. Our main goal was to determine which factors limit crayfish distribution, which could help to identify the most
effective management practices to contain its spread. Procambarus clarkii was found in most types of water bodies, including small and shallow ones. Distance to a crayfish source was the single predictor
variable explaining crayfish occurrence in most types of habitats and in both areas. The only exception was for the Sado permanent
stream points, where crayfish presence was negatively affected by an interaction between elevation and flow velocity. Other
habitat characteristics have apparently little or no importance for its successful colonization. Moreover, this study indicated
that overland dispersal is apparently a frequent phenomenon in this species. Our findings can be used to determine which habitats
are most likely to be colonized by the crayfish and to develop practical measures which may limit its spread and minimize
its impacts.
We compared ecological characteristics of three spatially independent invasions of the European green crab Carcinus maenas to determine which characteristics were most consistent across invasions, and hence would be most predictable in future invasions. For invasions in western North America (WNA), eastern North America (ENA), and South Africa (SAF), we compared five characteristics: (1) habitat usage, (2) diet preferences, (3) size of individuals, (4) rate of range expansion, and (5) demonstrated and potential impacts. We found that two characteristics, diet preference and ecological impact were relatively similar across the three invasions. Diet preference was particularly consistent with the rank order of taxa being virtually identical at the three sites. In contrast, habitat usage, individual size, and rate of range expansion were more variable. Differences in habitat usage and size were particularly evident in the WNA invasion, where C. maenas have failed to colonize protected and exposed rocky shores used elsewhere and have grown much larger than at other sites. We suggest that the degree of similarity of these characteristics across invasions provides a valuable measure of how predictable they will be in future invasions.
Haemolymph concentrations of chloride and sodium and osmotic pressure were measured in red swamp crayfish (Procambarus clarkii) and in white river crayfish (P. zonangulus) exposed to different temperatures and sodium chloride concentrations. Temperature affected the pattern of ionic concentrations of both species similarly with minimum concentrations at 24°C. Red swamp crayfish exhibited no statistically significant changes in sodium or osmotic pressure; howerver, chloride was significantly lower at 24°C than at higher or lower temperatures. White river crayfish had significantly higher values of all variables at temperatures higher and lower than 24°C. Crayfish exposed to salinities up to 20 ppt NaCl tended to hyperregulate their haemolymph osmotic pressure and chloride and sodium concentrations at the lower salinities. At about 20 ppt, the haemolymph became isosmotic or hyposmotic to the external solution. In crayfish transferred from freshwater to 20 ppt NaCl at different temperatures, haemolymph osmotic pressure and concentrations of chloride and sodium initially increased and were stabilized by 48 h in animals acclimated to 10, 15, 25, and 30°C.
The Chinese mitten crab Eriocheir sinensis is a native of freshwater and estuarine habitats along the east coast of Asia. Invasive populations have existed in northern Europe since the early 20th century, and more recently a breeding population has become established in the San Francisco Bay system along the west coast of North America. Ballast water is the most probable vector for both invasions, although there is also potential for escape from ethnic markets and from the ornamental aquarium industry. Invasive populations of mitten crabs have caused millions of dollars in economic and ecological damage. Economic impacts center largely on the burrowing activity of the crabs, which damages stream banks and levees, and the annual spawning migration, which interferes with fishing activities and irrigation projects. Chinese mitten crabs have recently appeared in the Chesapeake and Delaware Bays on the east coast of the USA, and there are confirmed reports of breeding females in both estuaries. The potential for large populations of mitten crabs in these estuaries has not been determined. This paper presents a review of the biology and ecology of native and invasive populations of the species and provides recommendations for research relevant to the prediction of future mitten crab invasions.
Osmotic and ionic regulation in the Crustacea is mostly accomplished by the multifunctional gills, together with the excretory organs. In addition to their role in gas exchange, the gills constitute organs of active, transepithelial, ion transport, an activity of major importance that underlies many essential physiological functions like osmoregulation, calcium homeostasis, ammonium excretion and extracellular pH regulation. This review focuses on structure–function relationships in crustacean gills and excretory effectors, from the organ to molecular levels of organization. We address the diversity of structural architectures encountered in different crustacean gill types, and in constituent cell types, before examining the physiological mechanisms of Na+, Cl−, Ca2+ and NH4+ transport, and of acid–base equivalents, based on findings obtained over the last two decades employing advanced techniques. The antennal and maxillary glands constitute the principal crustacean excretory organs, which have received less attention in functional studies. We examine the diversity present in antennal and maxillary gland architecture, highlighting the structural similarities between both organ types, and we analyze the functions ascribed to each glandular segment. Emphasis is given to volume and osmoregulatory functions, capacity to produce dilute urine in freshwater crustaceans, and the effect of acclimation salinity on urine volume and composition. The microanatomy and diversity of function ascribed to gills and excretory organs are appraised from an evolutionary perspective, and suggestions made as to future avenues of investigation that may elucidate evolutionary and adaptive trends underpinning the invasion and exploitation of novel habitats.
Juvenile lobsters survive well in salinities above 10.2% (300 mOsm/kg), and their osmotic and ionic (Cl-, Na+, Ca2+) regulation in dilute sea water is slightly hyperosmotic, similar to that of adults. Approximately a month after eyestalk ablation, osmotic and ionic (Cl-, Na+) regulation becomes isosmotic, water content increases, and survival rate in dilute sea water declines, but these changes can be partially reversed by implantation of eyestalk neuroendocrine tissue. Regulation of Ca2+, in contrast, is only slightly affected by eyestalk ablation. These results indicate that osmotic regulation and regulation of hemolymph Na+ and Cl- concentrations are at least partly controlled by eyestalk neuroendocrine factors in this species.
Intracellular free amino acids were measured in the abdominal muscle of the three larval instars, postlarvae, and juveniles of the lobster Homarus gammarus, acclimated to seawater (35 per thousand) and to a dilute medium (22 per thousand), to study intracellular isosmotic regulation throughout the development of this species. Transfer to low salinity was followed by a highly significant drop of free amino acids level in all developmental stages. The main regulated amino acids were glycine, proline, and alanine. The level of regulation of total free amino acids changed at metamorphosis: the decrease in total free amino acids at low salinity was 46% in the three larval instars, but it was only 29% in postlarvae and 20% in juveniles. These results suggest that free amino acids, mainly glycine, proline, and alanine, are involved in intracellular isosmotic regulation in the lobster, with different levels of involvement in pre- and postmetamorphic stages. The ontogenetic changes in intracellular isosmotic regulation are discussed in relation to the changes in extracellular regulation (osmoregulation) in the lobster.
The concentrations of free amino acids were measured in whole claw muscle, single fibres and haemolymph of Australian freshwater crayfish, Cherax destructor, during the intermoult stage. The average total pool of amino acids in short-sarcomere fibres (179 mmol kg(-1)) was 60% greater than in long-sarcomere fibres, due to higher concentrations of alanine, cysteine, glutamate, leucine and proline. The two fibre types exhibited differences in the banding pattern of the isoforms of troponin using gel electrophoresis. The average pool of amino acids in haemolymph was 2.7 mmol kg(-1). Cherax has symmetrical claws and the total pool of amino acids from whole muscles (approx. 79 mmol kg(-1)) was similar in left and right claw muscles. In animals acclimated to osmotic environments between 0 and 220 mOsm, the osmotic pressure of the haemolymph increased from 356 to 496 mOsm, but no systematic changes were observed in the amino acid profiles of muscles or haemolymph. The major findings were that (a) concentrations of amino acids differed between the two major fibre types in claw muscle and (b) amino acids in the muscle fibres did not play a major part in intracellular osmoregulation in Cherax, suggesting this species is an anisosmotic regulator.
Osmoregulation was studied throughout the embryonic development of Astacus leptodactylus. Egg-carrying females were held in freshwater (FW) and in three dilute seawater media (200, 400, 600 mosm kg(-1), 6.8, 13.6, 20.4 per thousand salinity). In FW, changes in peri-embryonic fluid (PEF) and (when available) embryonic hemolymph osmolality were followed from newly-laid eggs to hatching (for an embryonic eye index, EI, of 430-450 microm) and in first-stage juveniles. The PEF and/or hemolymph osmolality remained stable at about 360-380 mosm kg(-1) from early to late (EI 410 microm) embryos; it decreased prior to hatching (EI 420 microm) and in newly-hatched juveniles, down to 290 mosm kg(-1). Artificial opening and removal of the egg membranes, followed by direct exposure to FW, demonstrated that the ability to hyper-osmoregulate, and consequently to survive, in FW appears in embryos with EI > or = 410 microm, i.e., only a few hours or days before hatching. Following a transfer to the dilute seawater media, the PEF/hemolymph osmolality increased slowly over 18-20 days and became isosmotic with the external media at 13.6 and 20.4 per thousand. The embryos died at EI 380-395 microm in these media, and only at 6.8 per thousand was the development completed until successful hatch. These results demonstrate that (1) the embryos become able to osmoregulate in FW shortly before hatching, (2) the embryos are osmo-protected in the eggs during their development, (3) embryonic development and hatching are possible up to a salinity of 7 per thousand. These results are discussed in relation to freshwater adaptation of crayfish.
Under hyper-salinity stress from freshwater to 17 and 25 ppt seawater, red swamp crayfish Procambarus clarkii largely accumulated D- and L-alanine together with glycine, L-glutamine, and L-proline in both muscle and hepatopancreas. The increases of D- and L-alanine in muscle were the highest in all amino acids and reached 6.8- and 5.4-fold, respectively, from freshwater to 25 ppt seawater. These results indicate that both D- and L-alanine are the most potent osmolytes for intracellular isosmotic regulation in crayfish as well as other crustaceans thus far examined. Under anoxia stress below 0.1 mg/l dissolved oxygen for 12 h and subsequent recovery in normoxia for 12 h in freshwater, 17 and 25 ppt seawater, muscle ATP decreased dramatically in all salinity levels and almost depleted in seawater. Along with the decrease of muscle glycogen level, the significant increase of L-lactate was found in muscle, hepatopancreas, and hemolymph for each salinity level, suggesting the transport of L-lactate from muscle into hepatopancreas via hemolymph. Under anoxia, D- and L-alanine also largely increased in both muscle and hepatopancreas for each salinity level. The increase was much higher in seawater than in freshwater. Thus, both D- and L-alanine are possible to be anaerobic end products during prolonged anaerobiosis of this species.
The sodium pump, or Na(+)+K(+)-ATPase, provides at least part of the driving force for transepithelial movement of monovalent ions across the gills and other transporting tissues in many aquatic animals including the Crustacea. The crustacean Na(+)+K(+)-ATPase, like that in all animal cells, is composed of a catalytic alpha-subunit and an accompanying beta-subunit. The amino acid sequence of the crustacean alpha-subunit is 71-74% identical to vertebrate alpha-subunit sequences. In brachyuran Crustacea, the Na(+)+K(+)-ATPase is more highly expressed in posterior gills compared with anterior and is found predominantly in mitochondria-rich cells that are morphologically and biochemically specialized to mediate NaCl uptake from the medium. When the external salinity is lowered from that of normal seawater, producing conditions in which many euryhaline Crustacea hyperosmo regulate their hemolymph, both the enzymatic activity of the Na(+)+K(+)-ATPase and the gene expression of the alpha-subunit are increased in these tissues. Although the precise regulatory mechanism is not known, evidence suggests that crustacean hyperglycemic hormone may be responsible for the induction of Na(+)+K(+)-ATPase activity. Whether it also plays a role in activation of gene transcription is not known. A comparison of a range of aquatic Crustacea suggests that the level of Na(+)+K(+)-ATPase function in transporting tissues may be correlated with their ability to invade estuarine habitats.
The ontogeny of osmoregulation, the development of branchial transporting epithelia and the expression of the enzyme Na+/K+-ATPase were studied in Carcinus maenas (L.) obtained from the North Sea, Germany. Laboratory-reared zoea larvae, megalopae and young crabs were exposed to a wide range of salinities, and hemolymph osmolality was measured after 24 h exposure time (72 h in juveniles). Zoea I larvae slightly hyper-regulated in dilute media (10.2 per thousand and 17.0 per thousand ) and osmoconformed at >17 per thousand. All later zoeal stages (II-IV) osmoconformed in salinities from 10.2 per thousand to 44.3 per thousand. The megalopa hyper-regulated at salinities from 10.2 to 25.5 per thousand. Young crabs hyperregulated at salinities from 5.3 per thousand to 25.5 per thousand, showing an increase in their osmoregulatory capacity. The development of transporting epithelia and the expression of Na+/K+-ATPase were investigated by means of transmission electron microscopy and immunofluorescence microscopy. In the zoea IV, only a very light fluorescence staining was observed in gill buds. Epithelial cells were rather undifferentiated, without showing any features of ionocytes. Gills were present in the megalopa, where Na+/K+-ATPase was located in basal filaments of the posterior gills. In crab I juveniles and adults, Na+/K+-ATPase was noted in the three most posterior pairs of gills, but lacking in anterior gills. Ionocytes could first be recognized in filaments of megalopal posterior gills, persisting through subsequent stages at the same location. Thus, the development of the gills and the expression of Na+/K+-ATPase are closely correlated with the ontogeny of osmoregulatory abilities. The morphological two-step metamorphosis of C. maenas can also be regarded as an osmo-physiological metamorphosis, (i) from the osmoconforming zoeal stages to the weakly regulating megalopa, and (ii) to the effectively hyper-regulating juvenile and adult crabs.