Osmoregulatory Capacity Research Articles

Effect of sudden salinity change on Penaeus latisulcatus Kishinouye osmoregulation, ionoregulation and condition in inland saline water and potassium-fortified inland saline water

Two trials were conducted to determine the effect of sudden decrease in salinity of raw and potassium-fortified inland saline water on western king prawn Penaeus latisulcatus osmoregulation, ionoregulation and condition. Prawns were subjected to salinity decrease over 1 h from 32 to 25 ppt in the first trial and from 27 to 20 ppt in the second trial in three water types: inland saline water with potassium fortified to 100% and 80% of the marine water concentration (IS100, IS80), and raw inland saline water (ISW). In the first trial condition and ingestion rate were monitored over 19 days following salinity change. In the second trial condition, haemolymph osmo- and iono-regulation were recorded over 48 h following salinity change. In the first trial, 100% mortality was observed in ISW by day 13, with final survival 94% in IS80 and 100% in IS100. Tail muscle moisture content increased significantly (P < 0.05) over time in both trials and in all water types, suggesting loss of energy reserves. In the second trial, serum osmolality, sodium concentration and osmoregulatory capacity decreased following salinity change, stabilising by 24 h in IS100 and IS80 but continuing to decrease till 48 h in ISW, suggesting partial breakdown of osmoregulatory function in the potassium-deficient medium. Prawns were stronger regulators of divalent than monovalent cations. These trials demonstrate that potassium-deficient inland saline water requires fortification with potassium to allow prawn survival and efficient osmoregulation.

Oxygen Consumption and Osmoregulatory Capacity in Neomysis integer Reduce Competition for Resources among Mysid Shrimp in a Temperate Estuary

Results of field surveys and laboratory measurements of oxygen consumption and body fluid osmolality at different salinities in the mysids Neomysis integer, Mesopodopsis slabberi, and Rhopalophthalmus mediterraneus from the Guadalquivir estuary (southwest Spain) were used to test the hypothesis that osmotic stress (oxygen consumption vs. isosmotic points) was lowest at salinities that field distributions suggest are optimal. The three species showed overlapping spatial distributions within the estuary but clear segregation along the salinity gradient: N. integer, M. slabberi, and R. mediterraneus displayed maximal densities at lower, intermediate, and higher salinities, respectively. Adults of N. integer were extremely efficient hyperregulators (isosmotic point 30 per thousand) over the full salinity range tested (3 per thousand-32 per thousand), and their oxygen consumption rates were independent of salinity; adults of M. slabberi were strong hyper- and hyporegulators at salinities between 7 per thousand and 29 per thousand (isosmotic point, 21 per thousand) and showed higher oxygen consumptions at the lowest salinity (6 per thousand); adults of R. mediterraneus hyperregulated at salinities between 19 per thousand and seawater (isosmotic point, 36 per thousand), with the lowest oxygen consumption at salinity around their isosmotic point (35 per thousand). Thus, the osmoregulation capabilities of M. slabberi and R. mediterraneus seem to determine the salinity ranges in which most of their adults live, but this is not so for adults of N. integer. Moreover, maximal field densities of M. slabberi (males and females) and R. mediterraneus (males) occur at the same salinities as the lowest oxygen consumption. In contrast, field distribution of N. integer was clearly biased toward the lower end of the salinity ranges within which it osmoregulated. We hypothesize that the greater euryhalinity of N. integer makes it possible for this species to avoid competition with R. mediterraneus by inhabiting the more stressful oligohaline zone.

Effect of hypo- and hypersaline conditions on osmolality and Na+/K+-ATPase activity in juvenile shrimp (Litopenaeus vannamei) fed low- and high-HUFA diets

Fatty acid composition of cellular membranes can modify permeability and can modulate the activity of Na(+)/K(+)-ATPase. Although highly unsaturated fatty acids (HUFA) improve survival and osmoregulatory capacity to low salinities in penaeid shrimp, the possible mechanisms have not been established. For this purpose the influence of HUFA supplementation in diet (2.9 vs. 34% HUFA proportion to total fatty acids) on osmoregulatory responses of juvenile Litopenaeus vannamei submitted to an acute (15 h) or chronic exposure (21 days), to low (5 g L(-1)) and high salinities (50 g L(-1)) was analyzed. Shrimp fed the high-HUFA diet, had higher concentration of main HUFA (20:5n-3 and 22:6n-3) in polar lipids of gills. Osmotic pressure in hemolymph was significantly affected by salinity in acute (640, 751, 847 mOsm/kg for 5, 30 and 50 g L(-1), respectively), and chronic exposure (645, 713, 814 mOsm/kg), but variations between them were small compared to environmental salinity (206, 832, 1547 mOsm/kg), indicating that osmoregulation was achieved in a matter of hours. An increase in Na(+)/K(+)-ATPase activity was observed only after a chronic exposure to low salinity. Free amino acids (FAA), mainly alanine and arginine, were higher at 30 (control) and 50 g L(-1) in accordance to their role as organic osmolites. Neither osmotic pressure, Na(+)/K(+)-ATPase activity, nor FAA was affected by HUFA supplementation. However, higher water content in gills of shrimp exposed to low salinities was counteracted by increased HUFA content, which could be a result of changes in water permeability of gills. The osmoregulatory capacity of penaeid shrimp to low and high salinities was achieved within 15 h of acclimation and did not depend on HUFA supplementation in the diet.

Lack of an osmotic constraint on intake rate of the eastern curlew Numenius madagascariensis

Rates of food intake in animals consuming abundant prey can be constrained by the rates of digestion or excretion of ingested substances, such as salt, particularly so in the animals that regularly migrate between freshwater and saltwater environments. We tested this hypothesis in a long‐distance migrant shorebird, the eastern curlew Numenius madagascariensis (suborder Charadrii), foraging on intertidal decapods in eastern Australia. We predicted that if food intake rates are constrained osmotically, individuals with access to freshwater and less saline prey (FW group) would have higher rates of food and water intake than individuals with seawater‐only access (SW group). Food intake rates did not differ between the FW and SW groups (0.14 g ash‐free dry mass min−1), nor did the water influx rates (0.75 g min−1). Salt intake rates were lower at FW sites (19.3 versus 23.3 mg NaCl min−1) and overall they were similar to those of marine birds. Food intake rate in the eastern curlew appeared limited by digestive rather than by osmoregulatory capacity.

Comparison of growth, osmoregulatory capacity, ionic regulation and organosomatic indices of black tiger prawn ( Penaeus monodon Fabricius, 1798) juveniles reared in potassium fortified inland saline water and ocean water at different salinities

Growth, osmoregulatory capacity, ionic regulation and organosomatic indices of black tiger prawn ( Penaeus monodon Fabricius, 1798) juveniles (2.6 ± 0.2 g mean initial weight) were studied for 28 days in two water types namely inland saline water fortified with 100% K + (ISW 100) as in ocean water (OW) and OW. Three different salinities (5, 25 and 45 ppt) of each water type were prepared. No water type or salinity affected the survival of juveniles. The highest specific growth rate (SGR) was observed at 25 ppt in OW (4.7 ± 0.2%/day) and ISW 100 (4.1 ± 0.1%/day). The serum osmolality was hyper-regulated and hypo-regulated in salinities below and above isosmotic points respectively. There was no significant difference ( P > 0.05) between osmoregulatory capacity (OC) of juveniles in ISW 100 and OW at any salinity or time, except at 25 ppt. Except exoskeleton moisture content (EM%) of the juveniles reared in OW, there were no significant differences ( P > 0.05) among any organosomatic indices of the juveniles reared in ISW 100 and OW. At 5 and 45 ppt, in both water types, serum Na +, K + and Ca 2+ concentrations were strongly regulated above and below isoionic points. However, the serum Mg 2+ concentration was reduced below the medium Mg 2+ concentrations at all salinities. The ability of P. monodon juveniles to regulate these ions in inland saline water (ISW) was improved by fortifying K + in ISW to a similar level as in OW. The present trial thus augments the importance of fortification of K + in ISW to a similar level as in OW for P. monodon culture.

The growth and survival of western king prawns, Penaeus latisulcatus Kishinouye, in potassium-fortified inland saline water

Western king prawns, Penaeus latisulcatus are a candidate species for culture in inland saline water. Western king prawn survival, growth, condition, osmo- and iono-regulation was studied when reared in potassium-fortified inland saline water for 202 days. PL40 prawns were stocked into three media in 250 L tanks: inland saline water with potassium fortified to 80% (IS80) of the marine water concentration, 100% (IS100) of the marine water concentration and marine water (MW). By the conclusion of the trial, survival was 53% in IS80, 64% in IS100 and 68% in MW. Mean prawn weight, total length, carapace length, condition factor and moult interval were significantly higher ( P < 0.05) in MW than in IS100 and IS80. Specific growth rate of prawns in MW was significantly higher ( P < 0.05) than in IS80. There were no significant differences ( P > 0.05) in osmoregulatory capacity of prawns between various media. Serum Na +, K +, Ca 2+and S concentrations were influenced by their concentration in the medium. Ca 2+ was the only major cation hyper-regulated and tended to be accumulated, while Mg 2+ was maintained at a much lower concentration in the serum than in the medium. Moisture contents in hepatopancreas, tail muscle and exoskeleton and organosomatic indices improved from IS80 to IS100 to MW. The lower growth rates and condition factors of prawns reared in potassium-fortified inland saline water suggests the presence of limiting factors other than potassium concentration. Western king prawns are stronger regulators of divalent cations than monovalent cations and the extra energy required to regulate ions in inland saline water may have been the major cause of lower growth rates.

Water relations of phyllodinous and non‐phyllodinous Acacias, with particular reference to osmotic adjustment

An investigation was made into the effects of long‐ and short‐term water stress on the growth and water relations of species of Acacia belonging to four major sections of the subgenus Phyllodineae; the bipinnate‐leaved Botrycephalae and the phyllodinous Juliflorae, Phyllodineae and Plurinerves. The germplasm was collected from sites within a narrow rainfall band [700–800 mm mean annual rainfall (m.a.r.)]. Shoot and root mass were significantly decreased in three of the four sections by water stress. The exception was the Juliflorae that showed a conservative growth strategy. A high root/shoot ratio is associated with tolerance to arid or semiarid environments, however, the highest root/shoot ratio was found for the temperate Botrycephalae. Measurements were made of the capacity for active and partial osmoregulation. All sections showed a biphasic response to drought stress for natural logarithm plots of relative water content (RWC) vs. osmotic potential in one or both experiments. This pattern of response has previously only been reported in a few plant species. Osmotic adjustment (OA) ranged from 1.6 MPa for the Botrycephalae to 3.4 MPa for Juliflorae at RWC of 60%. Active osmoregulation in the second phase was lower for the Botrycephalae and Phyllodineae than for the Juliflorae and Plurinerves. Although the germplasm was collected within a narrow and relatively high m.a.r. band, the sections with arid and semiarid relatives (Juliflorae and Plurinerves) still retained a higher degree of xeromorphic character and drought tolerance as determined by the growth responses and the higher capacity for OA.

Sweet problems: insect traits defining the limits to dietary sugar utilisation by the pea aphid,Acyrthosiphon pisum

Plant phloem sap is an extreme diet for animals, partly because of its high and variable sugar content. The physiological and feeding traits of the pea aphid Acyrthosiphon pisum that define the upper and lower limits to the range of dietary sucrose concentrations utilised by this insect were determined principally using chemically defined diets containing 0.125-1.5 mol l(-1) sucrose. On the diets with 0.125 mol l(-1) and 1.5 mol l(-1) sucrose, the aphids died as larvae within 8 and 14 days of birth, respectively. On the other diets, 60-96% of aphids developed to adulthood, and the 0.5 mol l(-1) and 0.75 mol l(-1) diets supported the highest fecundity. The diet with 0.125 mol l(-1) sucrose was ingested at 36% of the rate of the 0.25 mol l(-1) sucrose diet, but >90% of ingested sucrose-carbon was assimilated on both diets. This suggests that the lower limit is dictated by the aphid feeding response, specifically, a requirement for a minimal concentration of sucrose for sustained feeding. The haemolymph osmotic pressure of aphids on diets with 0.125-1.5 mol l(-1) sucrose was up to 68% higher than on 0.125-1.0 mol l(-1) sucrose diets, but diet consumption and sucrose-carbon assimilation was not reduced on the very high sucrose diets relative to 1.0 mol l(-1) sucrose. This suggests that failure of the osmoregulatory capacity of the insects on high sucrose diets may define the upper limit to the range of dietary sucrose utilised by the aphids. The mean haemolymph osmotic pressure of aphids on plants with phloem sap containing 0.37-0.97 mol l(-1) sucrose was 1.61+/-0.063 MPa (mean +/- s.e.m.), not significantly different from that (1.47+/-0.059 MPa) on diets with 0.25-1.0 mol l(-1) sucrose. It is concluded that the osmoregulatory response of aphids to diets and plants are comparable, and, more generally, that the feeding and osmoregulatory capabilities of the aphids are compatible with the phloem sugar levels commonly encountered by aphids feeding on plants.

Effects of lecithin and cholesterol supplementation to practical diets for Litopenaeus vannamei reared in low salinity waters

The culture of shrimp in inland low salinity waters is a developing industry in many regions of the world, including west Alabama. These inland low salinity waters are often deficient in key ions necessary for normal physiological function. In west Alabama, farmers normally remedy ionic deficiencies in the water profile through the addition of fertilizers containing K+ and Mg2+. It has been suggested that increasing phospholipids (lecithin) and cholesterol in excess of dietary requirement improve osmoregulatory capacity in Litopenaeus vannamei, thus leading to better survival and growth under low salinity conditions. Cholesterol is an essential sterol involved in the molting process in shrimp. Phospholipids are important in cholesterol transport, facilitate the storage of lipids in the hepatopancreas, an important energy reserve during the molting process and are an important component of cell membranes. In order to investigate the possibility of improving growth and survival under stressful (i.e. low K+ and Mg2+) rearing conditions, a series of lab and on-farm experiments were conducted. Two separate 35 day laboratory studies were conducted in reconstituted low salinity (4.0 ppt, low K+) waters. In both trials, five practical diets were formulated to contain 36% protein and 8% lipid, and supplemented with varying levels of cholesterol and lecithin. Three of these diets were utilized for an additional experiment carried out on-site at two different low salinity shrimp farms in west Alabama. Results from the lab trials indicated no significant differences in survival, growth, or percent weight gain among treatments. Survival, final weight, and percent weight gain ranged from 68% to 77%, 2.70–3.0 g, 415–471% in experiment 1, and 56–69%, 2.7–3.2 g, 1572–1913% in experiment 2. These results indicate that the shrimp were stressed in both experiments, and there were no apparent benefits to supplementing lecithin and cholesterol in excess of the dietary requirement. Two on farm trials were conducted in parallel using either a mediated water source (Farm 1) to produce low stress or waters. At farm 1, survival, final weight, percent weight gain, and FCR ranged from 93.8% to 98.8%, 4.48–5.23 g, 4273–4901%, and 1.79–2.06, respectively. At farm 2 shrimp had lower survival (37.5–47.5%), lower final weight (2.65–3.25 g), lower percent weight gain (2342–3088%), and higher FCRs (6.85–10.64). No benefits from lecithin and cholesterol supplementation in excess of the dietary requirement were observed when compared to the basal diet under any test conditions. Based on results of the present study, dietary supplementation of cholesterol and phospholipids in excess of the requirement is not warranted for L. vannamei reared in low salinity waters.

Osmoregulatory capacity and the ability to use marine food sources in two coastal songbirds (Cinclodes: Furnariidae) along a latitudinal gradient

Cinclodes nigrofumosus and C. oustaleti are two closely related songbirds that inhabit the northern Chilean coast during the austral fall and winter. This stretch spans a dramatic north to south latitudinal gradient in rainfall and temperature. Whereas C. nigrofumosus lives exclusively on coastal environments, C. oustaleti shifts seasonally from coastal environments to inland freshwater ones. We used the delta13C of these two species' tissues to investigate whether the reliance on marine versus terrestrial sources varied from the hyper-arid north to the wet south. We also investigated latitudinal variation in the renal traits that mediate how these birds cope with dehydration and a salty marine diet. Both species increased the incorporation of terrestrial carbon, as measured by delta13C, as terrestrial productivity increased southwards. However, C. nigrofumosus had consistently more positive (i.e. more marine) and less variable delta13C values than C. oustaleti. The osmoregulatory traits of both species varied with latitude as well. Urine osmolality decreased from extremely high values in the north to moderate values in the south, while C. nigrofumosus produced more concentrated urine than C. oustaleti. In both species, the proportion of kidney devoted to medullary tissue decreased from north to south, and kidney size increased significantly with latitude. Cinclodes nigrofumosus had larger kidneys with larger proportions of medullary tissue than C. oustaleti. C. nigrofumosus and C. oustaleti are terrestrial organisms subsidized by a rich marine environment where it is adjacent to an unproductive terrestrial. Variation in the reliance on marine food sources seems to be accompanied by adjustments in the osmoregulatory mechanisms used by these birds to cope with salt and dehydration.

Temperature dependence of water loss rates in scorpions and its effect on the distribution of Buthotus judaicus (Buthidae) in Israel

Scorpions of the family Buthidae have been shown to be more desiccation resistant in comparison with sympatric Scorpionidae species. This has been attributed to the surface-dwelling existence of the former, which unlike most other scorpion species do not avoid environmental extremes by burrowing. Still, within Buthidae, the mesic Buthotus judaicus showed better osmoregulatory capacities than the xeric Leiurus quinquestriatus, largely as a result of its high resistance to water loss. However, B. judaicus exhibited poor ability to regulate its haemolymph osmolarity at 37 °C. In this study we report a sharp increase in water loss rates of B. judaicus at the 30–35 °C temperature range compared to that measured for L. quinquestriatus, which could explain the poor osmoregulatory performance of the former at higher ambient temperatures. The increase in water loss rates of B. judaicus at high temperatures is not coupled with a similar increase in respiratory rate, suggesting an increase in cuticular permeability. We suggest that this increase in cuticular permeability, which may result from a relatively low critical transition temperature, contributes to limiting the distribution of B. judaicus to habitats of moderate environmental conditions.

Field distribution and osmoregulatory capacity of shrimps in a temperate European estuary (SW Spain)

The spatial distribution of the six most common crustacean decapods in the benthos and hyperbenthos of the Guadalquivir estuary (SW Spain) has been analysed in relation to their osmoregulatory capacities (at 20 °C). Field densities along the estuarine salinity gradient revealed that, although the species studied showed salinity tolerance ranges in the field that do overlap to some extent, there was a considerable spatial and/or salinity-related segregation between several of them. Concerning their isosmotic points and their osmoregulatory salinity ranges, two main groups of species were distinguished: species with higher isosmotic points and tight ranges in osmoregulation, represented by marine species that entered the estuary from open sea and remained there for only part of the year ( Crangon crangon, Melicertus kerathurus and Palaemon serratus); and those with slightly lower isosmotic points and wide ranges in osmoregulation, represented by estuarine species which completed their life cycle in brackish water ( Palaemon longirostris, Palaemon macrodactylus and Palaemonetes varians). For all the species studied, their field distributions were clearly biased towards the lower end of the salinity ranges within which they osmoregulate. Nevertheless, individuals of the less euryhaline species ( M. kerathurus and P. serratus) were mainly found in less saline water when the estuarine gradient was displaced downstream and low salinities occurred close to the river mouth.

Osmoregulation, Immunolocalization of Na+/K+‐ATPase, and Ultrastructure of Branchial Epithelia in the Developing Brown Shrimp,Crangon crangon(Decapoda, Caridea)

Aspects of osmoregulation including salinity tolerance, osmoregulatory capacity, location of transporting epithelia, and the expression of the enzyme Na+/K+-ATPase were investigated in the developing brown shrimp, Crangon crangon (L.), from the North Sea. Early developmental stages and large juveniles were exposed to a wide range of salinities for measurement of hemolymph osmolality and survival rates. In media ranging from 17.0 per thousand to 32.2 per thousand, salinity tolerance was generally high (survival rates: 70%-100%) in all developmental stages, but it decreased in media <10.2 per thousand. Zoeal stages and decapodids slightly hyperregulated at 17.0 per thousand and osmoconformed in media > or =25.5 per thousand. At 10.2 per thousand, these stages showed high mortality, and only juveniles survived at 5.3 per thousand. Juveniles hyperregulated at 10.2 per thousand and 17.0 per thousand, osmoconformed at 25.5 per thousand, and hyporegulated in media > or =32.2 per thousand. Large juveniles hyperregulated also at 5.3 per thousand. Expression of the Na+/K+-ATPase and ion-transporting cells was located through immunofluorescence microscopy and transmission electron microscopy. In zoeae I and VI, a strong immunoreactivity was observed in cells of the inner epithelia of the branchiostegites and in epithelial cells lining the pleurae. Their ultrastructure showed typical features of ion-transporting cells. In decapodids and juveniles, ionocytes and expression of Na+/K+-ATPase remained located in the branchiostegite epithelium, but they disappeared from the pleurae and appeared in the epipodites. In large juveniles, the cells of the gill shaft showed positive immunolabeling and ultrastructural features of ionocytes. In summary, the adult pattern of osmoregulation in C. crangon is accomplished after metamorphosis from a moderately hyperosmoconforming decapodid to an effectively hyper-/hyporegulating juvenile stage. Salinity tolerance and osmoregulatory capacity are closely correlated with the development of ion-transporting cells and the expression of Na+/K+-ATPase.

Biochemical, physiological, and immunological changes during starvation in juveniles of Litopenaeus vannamei

In an attempt to know how the protein level modulates catabolism and its effects on the immune response, we studied juvenile L. vannamei that had been starved for varying period after being conditioned on diet containing either maintenance or optimal dietary protein levels (DPL). The effect of dietary protein level on nutritional reserves management of shrimp and its relation with immune condition was also addressed. Juvenile shrimp were fed for 21 days on diets containing 5% and 40% dietary protein. Hemolymph metabolites (glucose, cholesterol, protein, acylglycerols, and lactate), hemocyanin, osmoregulatory capacity, digestive gland glycogen and lipids, and immune conditions (hemocytes characterization, phenoloxidase activity, respiratory burst: basal and activated) were evaluated and considered as initial condition. After that time, shrimp were starved for 21 days. During starvation time every 7 days nutritional, physiological and immunological condition were evaluated. A reduction in all physiological and immunological indicators was observed with starvation. The protein level of the conditioning diet had a significant effect on this response; generally, the effect was smaller with shrimp previously fed 40% dietary protein. In this sense the present results demonstrate that shrimp are well adapted to tolerate food deprivation for some time but that this tolerance is closely related to its previous nutritional condition. In the case of shrimp fed 40% DPL, wet weight, nutritional and immune condition was significantly affected after 14 days of starvation. In shrimp previously fed 5% DP, tolerance to starving condition was limited to only a few days (7 days) as a result of low reserves of circulatory and mussel proteins. All these results demonstrate that dietary protein levels can governor the immune condition of shrimp through the management reserves metabolism, indicating that a shrimp with a good nutritional condition can tolerate until 14 days without modifying the evaluated immune responses. In this sense it can be concluded that protein metabolism have a central role for shrimp.

The effect of desiccation on water management and compartmentalisation in scorpions: the hepatopancreas as a water reservoir

Scorpions of the Family Buthidae have lower water loss rates (WLR) and enhanced osmoregulatory capacities in comparison with sympatric species of F. Scorpionidae. In this study we followed changes in water content of different body compartments in four scorpion species under prolonged desiccation conditions. The high initial WLR previously reported for Scorpionidae result in rapid depletion of body water stores. A significant decrease in total body water content of Scorpionidae was recorded following loss of only 5% of initial mass, whereas no such decrease was recorded for Buthidae following severe desiccation. When desiccated, scorpions lose water primarily from the hepatopancreas, while haemolymph volume is more tightly regulated. However, the haemolymph volume of Scorpionidae decreases as a result of depletion of hepatopancreas water stores following severe desiccation. The increasing lipid fraction in the hepatopancreas of Scorpionidae during desiccation suggests that depletion of body water stores may induce enhanced catabolism of carbohydrates, which may contribute to volume regulation by making initially glycogen-bound water available to the desiccating scorpion.

Ontogeny of salinity tolerance and hyper-osmoregulation by embryos of the intertidal crabs Hemigrapsus edwardsii and Hemigrapsus crenulatus (Decapoda, Grapsidae): Survival of acute hyposaline exposure

The adults of Hemigrapsus edwardsii and Hemigrapsus crenulatus are euryhaline crabs and strong hyper-osmoregulators. Their embryos are carried externally attached to the abdominal pleopods of female crabs, where they are exposed to temporal and spatial changes in salinity associated with their intertidal and estuarine habitats. Although embryos lack the branchial and excretory organs responsible for adult osmoregulation, post-gastrula embryos were highly tolerant of exposure to hypo-osmotic sea water. Detached eggs (embryos + envelopes), of both species, at all developmental stages between gastrulation and hatching, exhibited 80–100% survival for periods up to 96 h in sea water (osmolality, 1050 mmol kg − 1 ) and in dilutions to 50%, 10%, and 1%. Cleavage stages were less tolerant of dilution; H. edwardsii, < 50% survived 24 h in 10% sea water; H. crenulatus < 50% survived 6 h in 10% sea water. Post-gastrulation stages strongly hyper-osmoregulated but cleavage stages were hyper-osmoconformers (maintaining internal osmolality ≈ 150 mmol kg − 1 above external). Osmoregulatory capacity was reduced just prior hatching, particularly in H. crenulatus, although salinity tolerance remained high. Gastrulation therefore marks a critical stage in the ontogeny of osmoregulation and salinity tolerance. Total Na +/K +-ATPase activity increased greatly during embryogenesis of H. crenulatus (undetectable in blastulae; gastrulae 0.31 ± 0.05 pmol P i embryo − 1 min − 1 ; pre-hatching 16.4 ± 1.0 pmol P i embryo − 1 min − 1 ). Na +/K +-ATPase activity increased in embryos exposed to dilute sea water for 24 h implicating regulation of this transporter in a short-term acclimation response.

Effects of the interaction between drought and shade on water relations, gas exchange and morphological traits in cork oak ( Quercus suber L.) seedlings

The combined effect of drought and light on different physiological and biochemical traits was assessed in cork oak ( Quercus suber L.) seedlings grown under two levels of light availability and submitted to a long-standing drought. Watering was withdrawn after germination and seedlings were allowed to dry to a water content of ca. 50% of field capacity. At this point, water-stressed seedlings were grown under moderate drought and two light regimes: high light (HL—50%) and low light (LL—2%). Soil water in control plants was kept close to field capacity (90–100%) for both light environments. Water-relations parameters derived from P– V curves, gas exchange and water status at predawn ( Ψ pd) were evaluated at twice during the experiment. Nitrogen and chlorophyll contents were determined in the same leaves used for the gas exchange measurements. In addition, maximum rate of carboxylation ( V cmax) and electronic transport ( J max) were derived from A– C i curves in well-watered seedlings. The variation on moisture availability during the experiment was the same under both light environments. In control plants, Ψ pd was over −0.3 MPa at the two harvests, while stressed seedlings decreased to −0.9 MPa, with no differences between light treatments. Water stress decreased osmotic potentials at full ( Ψπ 100) and zero turgor ( Ψπ 0). The regressions between both potentials and Ψ pd showed a higher intercept in shade grown seedlings. This fact will point out the higher osmoregulation capacity in sun seedlings whatever water availability. Nitrogen investment on a per leaf mass ( N mass), chlorophyll content (Chl mass) and SLA tended to show a typical pattern of sun-shade acclimation. Thus, the three parameters increased with shade. Only for N mass there was a significant effect of watering, since water stress increased N mass. LL plants showed a lower photosynthetic capacity in terms of maximum net photosynthesis at saturating light ( A max), which was related to a decrease in V cmax and J max. Both parameters varied with specific leaf area (SLA) in a similar way. The low-light environment brought about a higher nitrogen investment in chlorophyll, while under high-light environment the investment was higher in carboxylation ( V cmax) and electronic transport ( F max). Stomatal conductance to water vapour ( g wv) and A max were lower in low-light seedlings independently of watering. In addition, there was a trend to keep higher intrinsic water use efficiency (IWUE) under high light environment. The increase of IWUE under water stress was higher in HL seedlings. This was as consequence of the steeper decline in g wv as Ψ pd decreased. The decrease of A max with Ψ pd occurred in a similar way in LL and HL seedlings. Thus, the HL seedlings tended to sustain a higher ability to increase IWUE than LL seedlings when they were submitted to the same water stress.

The Effects of Air Exposure on Hemolymph Osmoregulatory Capacity of Brown Tiger Shrimp, Penaeus esculentus, and Western King Shrimp, Penaeus latisulcatus, Reared at Different Salinities

Hemolymph osmolality and osmoregulatory capacity (OC) of brown tiger shrimp, Penaeus esculentus (0.94±0.04 g mean initial weight) and western king shrimp, P. latisulcatus (5.37±0.10 g mean initial weight) from four salinities (10, 22, 34 and 46 ppt) were determined following 7, 14 and 21 minutes of air-exposure. Hemolymph osmolality of both species increased with increasing salinity. Isosmotic points of brown tiger shrimp calculated from regression lines between hemolymph and medium osmolality were 30.9, 31.9, 32.1 and 31.1 ppt at 0, 7, 14, and 21 minutes of air-exposure, respectively. Isosmotic points of western king shrimp were 33.8, 33.3, 32.8 and 33.1 ppt at 0, 7, 14, and 21 minutes air-exposure, respectively. OC of brown tiger shrimp at salinity of 34 ppt did not change when exposed to air for any length whereas OC of shrimp at other salinities (10, 22 and 46 ppt) were significantly different (P < 0.05) when exposed to air for 21 minutes. OC of western king shrimp at salinity 10 ppt was reduced (P < 0.05) when exposed to 14 and 21 minutes of air when compared to control and 7 minutes of air exposure. The results indicate that both species spent less energy (P < 0.5) for osmoregulation from 30 to 34 ppt. Furthermore, salinities 10 and 46 ppt were unsuitable for rearing brown tiger shrimp and salinity 10 ppt was unsuitable for growing western king shrimp.

Selenium modulates the activities of antioxidant enzymes, osmotic homeostasis and promotes the growth of sorrel seedlings under salt stress

Using physiological assays coupled with ultrathin tissue sections, we investigated the impacts of exogenous selenium (Se) on the growth, antioxidant enzymes, osmotic regulation and ultrastructural modifications of leaf mesophyll and root tip cells of 100 mM NaCl-stressed sorrel (Rumex patientia × R. tianshanicus) seedlings. At low concentrations (1–5 μM), Se tended to stimulate the growth, the activities of superoxide dismutase and peroxidase enzymes, as well as the accumulation of water-soluble sugar in leaves of sorrel seedlings. At higher concentrations (10–30 μM), Se exerted diminished beneficial effects on growth and enzyme activities. CAT activity did not change with Se addition (1–30 μM). Electrolyte leakage of leaf cells declined, and K+ and Na+ ions increased in leaves with Se treatment, notably at 5 μM of Se. TEM observations revealed that treatment with 5 μM of Se positively promoted the integrity of membrane systems and cellular organelles, such as chloroplasts and mitochondria in leaf mesophyll and root tip cells. These results strongly suggest that an appropriate concentration of exogenous Se functions positively to promote the antioxidative and osmoregulatory capacity, and enhance the salt-resistance in sorrel seedlings.

Effects of salinity on embryonic development of Palaemonetes argentinus (Crustacea: Decapoda: Palaemonidae) cultured in vitro

Summary The shrimp Palaemonetes argentinus Nobili 1901 inhabits freshwater streams, lakes and brackish coastal lagoons in the warm temperate regions of southeastern South America. Larvae and adults tolerate a wide range of salinities, exhibiting a well developed osmoregulatory capacity already from hatching. Nevertheless, effects of salinity on the embryos of P. argentinus have not been studied yet. In the present investigation, freshly layed eggs were removed from ten females and, from the time of extrusion to larval hatching, exposed in vitro to four salinities (1, 15, 25, 32 PSU; all incubated at 20°C). This technique allowed the comparison of salinity effects on embryos of the same brood, excluding maternal effects as potentially confounding sources of variation. Initial egg size and duration of embryonic development under identical conditions varied significantly among broods from different females, but showed no significant relationships with female body size. Development was most successful in eggs incubated at salinities of 1 and 15 PSU, with average hatching rates of 72% and 79%, respectively. In contrast, 20% hatched at 25 PSU, and only three individuals (1.5%) in seawater (32 PSU). Egg mortality increased consistently near the end of the developmental period, especially at 25 and 32 PSU. Larvae hatching at these relatively high salinities retained a greater quantity of yolk, while many were deformed, suggesting that hyperosmotic stress interfered with metabolic energy mobilization and morphogenetic processes. The mean time from spawning of the eggs to larval hatching was similar at 1 and 15 PSU (ca. 24 d), but lasted significantly longer at 25 and 32 PSU (26–27 d, respectively). During the first ca. 10–12 days of embryonic development, the volume of the eggs decreased slightly at 25 and 32 PSU, while an increase was observed at lower salinities (maximum: 20% at 1 PSU). During the final period of development, an increase in egg volume occurred in all treatments, being significantly stronger at low salinities (≤15 PSU). The first zoeal stage of P. argentinus can also in complete absence of food successfully develop from hatching through the moult to the zoea-II stage; this trait (facultative lecithotrophy) was not affected by salinity. Our results suggest that successful reproduction of P. argentinus in freshwater and brackish habitats with highly variable conditions of salinity and food availability is based on an early appearance of osmoregulatory functions during the embryonic phase and/or a low permeability for ions of the egg membrane, while yolk reserves persisting from the egg allow for food-independent development through the first larval stage.