Reduced hypoosmoregulatory ability and alteration in gill chloride cell distribution in mature chum salmon (Oncorhynchus keta) migrating upstream for spawning

Osmoregulatory ability of mature chum salmon (Oncorhynchus keta) during spawning migration was examined by following the changes in gill Na⁺, K⁺-ATPase activity and in the distribution and morphology of chloride cells. Mature chum salmon caught in Otsuchi Bay, northern Honshu Island, Japan, died within 5 d in seawater (SW) in association with a marked increase in plasma osmolality, whereas the fish transferred to fresh water (FW) maintained plasma osmolality efficiently. Gill Na⁺, K⁺-ATPase activity decreased in both SW-maintained and FW-transferred fish. Well-developed chloride cells, identified by immunocytochemical staining specific for Na⁺, K⁺-ATPase, were present mainly in the filament epithelium of immature fish caught in the ocean. In mature fish caught in the bay, however, additional chloride cells were also found in the lamellar epithelium. The number of filament chloride cells decreased markedly in the mature fish both in SW and in FW, whereas the number of lamellar chloride cells was maintained. These results suggest that the loss of hypoosmoregulatory ability in mature chum salmon may be attributable to the decrease in filament chloride cells and associated decrease in gill Na⁺, K⁺-ATPase activity, and also that appearance of lamellar chloride cells may be preparatory to the forthcoming upstream migration. Received: 14 April 1997 / Accepted: 5 May 1997     

Effect of copper on ion- and osmoregulation in the shore crab Carcinus maenas

The uptake and effect of dissolved copper on regulation of hemolymph osmolality and Na⁺, K⁺, Cl^-, Ca⁺⁺, and Mg⁺⁺ concentrations in the shore crab Carcinus maenas (L.) were determined at 400 mOsm (=14 S) ambient salinity. One mg Cu l^-1 resulted in 50% mortality in 11 to 22 d; the highest sensitivity was observed around the moulting period. 0.25 and 0.5 mg Cu l^-1 were not lethal after a onemonth exposure. Ten, 1, and 0.5 mg Cu l^-1 altered regulation of osmolality, Na⁺, K⁺, and Cl^- concentrations, while 0.25 mg Cu l^-1 did not. Exposure to 1 mg Cu l^-1 reduced hemolymph osmolality and Na⁺, K⁺, and Cl^- concentrations to 80 to 90% of controls within 4 to 6 d and no further reduction was observed during a 21-d exposure. The effect of various copper concentrations on these four parameters were almost identical and the highest sensitivity was observed around the moulting period. Hemolymph calcium levels increased 20 to 80% in crabs exposed to 1 mg Cu l^-1, while they decreased 20 to 30% in crabs exposed to 0.5 mg Cu l^-1. Prolonged exposure to copper caused 20 to 70% reductions in hemolymph magnesium levels. Crabs exposed to 0.5 mg Cu l^-1 for 29 d accumulated copper in hepatopancreas, gills, carapace, heart, testes, and hypodermis, but not in muscles and hemolymph. Increased copper levels in crabs exposed to 0.25 mg Cu l^-1 were observed in hepatopancreas, gills, and carapace only. The present results suggest that effects of copper on ion regulatory processes in part explain why the toxicity of copper towards euryhaline invertebrates increases at low salinities.     

Effect of salinity fluctuation on the osmotic pressure and Na+, Ca2+ and Mg2+ ion concentrations in the hemolymph of bivalve molluscs

Specimens of Chlamys opercularis, Modiolus modiolus, Mytilus edulis, Crassostrea gigas, Scrobicularia plana and Mya arenaria were exposed to both gradual (sinusoidal) and abrupt (square-wave) salinity fluctuations and measurements made of osmotic, Na⁺, Mg²⁺ and Ca²⁺ concentrations in the hemolymph and where applicable in the mantle fluid. In both sinusoidal and square-wave regimes fluctuating between 100 and 50% seawater (100%=ca. 32 S), the hemolymph Na⁺, Mg²⁺, Ca²⁺ and osmotic concentrations followed the concentrations of the external medium in Chlamys opercularis. The hemolymph and mantle fluid osmotic Na⁺, Mg²⁺ and Ca²⁺ concentrations of Modiolus modiolus, Mytilus edulis, Crassostrea gigas and S. plana followed those of the external medium as long as the molluscs' shell valves remained open. There were no changes in the ionic or osmotic concentrations of the hemolymph or mantle fluid of any of these species during periods of shell-valve closure. The hemolymph osmotic, Na⁺ and Mg²⁺ concentrations of wedged-open Modiolus modiolus, Mytilus edulis, C. gigas and S. plana followed those of the external medium. Hemolymph Ca²⁺ concentrations showed a damped response in C. gigas and Mytilus edulis. The hemolymph osmotic, Na⁺, Ca²⁺ and Mg²⁺ concentrations of Mya arenaria fluctuated in a similar manner to the external medium, but were damped. Wedged-open Mytilus edulis exposed to fluctuating salinity and supplied with a constant supply of 10 mM Ca²⁺ showed greater changes in hemolymph ionic and osmotic concentrations than M. edulis exposed to the same salinity fluctuation without a constant Ca²⁺ supply. Chlamys opercularis and Modiolus modiolus survived in a 50% seawater minimum sinusoidal salinity fluctuation for 10 days; wedged-open M. modiolus survived only 3 days. Burrowing had no effect on the osmotic, Na⁺, Mg²⁺ or Ca²⁺ concentrations of the hemolymph of Mya arenaria or S. plana exposed to fluctuating salinities. All of the species studied were shown to be osmoconformers.     

Alterations in plasma electrolyte levels of a freshwater fish Cyprinus carpio exposed to acidic pH

The impact of acidification (Low pH 5.0) on plasma electrolytes (Na⁺, K⁺, Cl^?, Ca²⁺, and Mg²⁺) in a freshwater fish Cyprinus carpio was studied for a 35 day (long term) exposure period, while control groups were maintained at neutral pH (7.3). During long-term (35 days) exposure periods, plasma K⁺ and Mg²⁺ levels were increased (77.8% and 16.0%) in the low pH (5.0) treated fish. On the other hand, plasma Na⁺, Cl^?, and Ca²⁺ levels were decreased (12.4%, 18.4% and 31.3%, respectively). The loss of plasma Na⁺, Cl^?, and Ca²⁺ indicates the displacement of Ca²⁺ from tight junctions. The increased plasma K⁺ ion might have resulted from acidosis, because intracellular K⁺ is released from muscle as H⁺ enters. The elevated level of plasma Mg²⁺ might be due to inhibition of active transport of magnesium across the kidneys resulting in the accumulation of this ion in the plasma. Ionic alteration takes place upon exposure to acidic pH and can be considered as a potential tool for detecting environmental stresses caused by acidification.     

Effects of ammonia on survival and osmoregulation of various development stages of the shrimp Penaeus japonicus

In Penaeus japonicus, the tolerance to ammonia increased with the development from nauplius to late juvenile. The 48-h LC₅₀ of ammonia in nauplii (III–V), 96-h LC₅₀ in zoeae (I–III), mysis (I–III), post-larvae (PL1) and late juveniles (10.4±1.1 g) were respectively 5.0, 6.1 to 8.1, 9.4 to 10.9, 15.5 and 52.7 mg Nl^-1 (0.5, 0.6 to 0.7, 0.9, 1.3 and 3.1 mg NH₃–Nl^-1). In a chronic experiment (20 d), the LC₅₀ in post-larvae (PL1) was 19.1 (1.4) at 96 h and 16.2 mg Nl^-1 (1.3 mg NH₃–Nl^-1) at 480 h. Osmoregulatory capacity (OC) was calculated as the osmotic gradient between the hemolymph and the external medium at given salinities. The effects of ammonia on OC, Na⁺ and Cl^- regulation and gill Na⁺–K⁺ ATPase activity in late juveniles were examined in fullstrength seawater, SW (1050 mosm kg^-1, 36 S) and in dilute SW (450 mosm kg^-1, 15%.), after 48 or 96 h exposure to various concentrations of ammonia. Ambient ammonia disrupted both hypo- and hyper-osmoregulation; decreased OC resulted from impaired Na⁺ and Cl^- regulation. Gill Na⁺–K⁺ ATPase activity increased in SW and was not affected in dilute SW. The decrease of OC was ammonia-dose-dependent. The threshold ammonia concentrations affecting hypo-OC and hyper-OC were, respectively, 16 (1.3) and 32 mg Nl^-1 (2.3 NH₃–Nl^-1) for a 48 h exposure; these concentrations were lower than the 48-h LC₅₀ value, 65.3 mg Nl^-1 (3.5 NH₃–Nl^-1). The time course of exposure to sublethal ammonia (48 mg Nl^-1) demonstrated that the effect on osmoregulation was time-dependent. This effect was also temporary, and the exposed shrimps recovered control OC values after removal of excessive ambient ammonia. The possibility of using OC as an indicator of physiological condition in osmoregulating crustaceans and the acting mode of ammonia on osmotic and ionic regulation are discussed.     

Water balance systems of Rangia cuneata: ionic and amino acid regulation in changing salinities

In order to study the interaction of the extracellular and intracellular osmoregulatory systems of the bivalve Rangia cuneata, we have measured blood osmotic and ionic concentrations together with intracellular free amino acid concentrations and total tissue water under identical salinity conditions. Like freshwater bivalves, the blood of R. cuneata is maintained hyperosmotic (50 mOsm) to the environment in salinities below 110 mosm by the regulation of Na⁺, Cl^-, K⁺ and Ca²⁺ concentrations. On the other hand in company with marine bivalves, R. cuneata also regulates intracellular free amino acids (FAA) as a mechanism to control cellular volume during osmotic stress over the entire non-lethal salinity range (3 to 620 mOsm). Alanine is the predominant intracellular osmotic effector. Thus, by utilizing the osmoregulatory mechanisms of both marine and freshwater bivalves, R. cuneata is able to tolerate salinities ranging from freshwater to 25 ppt and to traverse the faunal salinity boundary, known as the horohalinicum (5 to 8 ppt), controlling cell volume throughout.Please address requests for reprints to Dr. S. K. Pierce     

Osmotic properties of eggs of the herring Clupea harengus

Yolk osmolality of developing eggs of the herring Clupea harengus L. is strongly hypoosmotic to seawater: about 440 mOsm during the first week of development decreasing to 360 mOsm before hatching. The perivitelline fluid (PVF) of the eggs is isoosmotic to the ambient medium. The PVF equilibrates within 10 min to changes in the ambient seawater. The content of Na⁺, K⁺, Cl^- and free amino acids amount to 26, 52, 48, and 54 n mol egg^-1, respectively, on Days 1 to 3 after fertilization, increasing to 63, 69, 80, and 79 n mol egg^-1, respectively, prior to hatching (Days 18–20). The apparently conflicting findings of a decreasing yolk osmolality and a simultaneous increase in the amount of egg solutes are at present unexplained.     

Effects of tidal fluctuations of salinity on pericardial fluid composition of the American oyster Crassostrea virginica

Crassostrea virginica Gmelin were subjected to simulated tidal fluctuations of salinity, and the subsequent effects on osmotic and ionic composition of the pericardial fluid, body water and valve movements were investigated. Ambient salinity fluctuation patterns of 20-10-20, 15-10-15 and 10-5-10 were simulated during 24.8-h periods. An additional 10-5-10 S experiment was performed using a dilution water approximating the ionic composition of Mississippi River water with regard to Mg⁺⁺, Ca⁺⁺ and SO ₄ ⁼ , instead of deionized water. Finally the effects of a 2-week diurnal fluctuation pattern between 20 and 10 S were investigated with respect to pericardial fluid composition. Pericardial fluid osmolality, concentrations of Cl^-, Na⁺, Mg⁺⁺, K⁺, Ca⁺⁺ and ninhydrin-positive substances (NPS) were analyzed periodically throughout all experiments. Pericardial fluid osmolality was slightly hyperosmotic as ambient water salinity decreased during a cycle, and then became slightly hyposmotic as ambient salinity increased. In the 2-week experiment, pericardial fluid osmolality tracked ambient seawater closely through Day 5, but became more intermediate between high and low seawater values as the experiment progressed. Similar patterns during fluctuations of salinity were observed for Na⁺, Cl^-, Mg⁺⁺ and Ca⁺⁺. Pericardial fluid K⁺ levels did not track ambient seawater as closely as did other ions. The ionic composition of dilution water had little effect on the osmotic or ionic response of the oyster's pericardial fluid. Pericardial fluid NPS level varied inversely with salinity during the 20-10-20 cycle. During the longterm fluctuation experiment, NPS values gradually decreased over the 2-week period compared to constant salinity control values. Percent body water also varied inversely with ambient salinity. Solute movement accounted for most of the change in pericardial fluid osmolality during the simulated cycles with water movement responsible for 1 to 11%. Water movement contributed more to the change of pericardial fluid osmolality during the decreasing salinity phase than the increasing phase of a given cycle. During 20-10-20 S cycles, oyster valves remained open 56% of the time (n=23). In contrast, when salinity was abruptly changed from 20 to 10 within 5 min, valve closure occurred in 4.8±0.3 min (n=20). Valves did not reopen for 19.3±1.2 h (n=15).     

A comparison of transport-related gill enzyme activities and tissue-specific free amino acid concentrations of Baltic Sea (brackish water) and freshwater threespine sticklebacks, Gasterosteus aculeatus, after salinity and temperature acclimation

The osmoregulatory abilities of one freshwater and two brackish water (Baltic Sea) populations of the euryhaline teleost fish Gasterosteus aculeatus were studied with respect to evolutionary physiology. Plasma osmolality, activities of Na⁺K⁺-ATPase, citrate synthase, creatine kinase in the gill and free amino acids in liver, axial muscle and pectoral fin muscle were measured. After transfer from 10 to 35 ppt at 15 °C, time-course changes of plasma osmolality and gill Na⁺K⁺-ATPase showed no significant fundamental differences between the freshwater and one of the Baltic Sea populations. In a multi-factorial experiment, each population was exposed to four different abiotic regimes. Both brackish water populations had high mortality in freshwater at 4 °C, which is discussed as a failure of osmotic regulation (reduced taurine concentrations). Freshwater specimens had higher levels of glycine in the axial and pectoral fin muscles compared to the brackish water populations. This is interpreted as a genetically based effect. In brackish (20 ppt) water of 15 °C, the freshwater population had high activities of Na⁺K⁺-ATPase, but low activities of creatine kinase, whereas both brackish water populations behaved in the opposite way. A fundamental difference between the freshwater and brackish water populations on the level of the osmoregulatory machinery was not observed. Received: 10 December 1998 / Accepted: 22 September 1999     

Ontogenic change of gill chloride cells in leptocephalus and glass eel stages of the Japanese eel, <Emphasis Type="Italic">Anguilla japonica</Emphasis>

The development of gill chloride cells was examined in premetamorphic larvae (leptocephali) and juveniles (glass eels) of the Japanese eel, Anguilla japonica. Branchial chloride cells were detected by immunocytochemistry using an antiserum specific for Na⁺,K⁺-ATPase. The specificity and availability of the antiserum for the detection of Japanese eel chloride cells were confirmed by Western blot analysis. The chloride cells first appeared on the developing gill filaments in a mid larval stage of leptocephalus (32.2 mm). Both immunoreactivity and the number of chloride cells gradually increased as the fish grew to a late stage of leptocephalus over 54 mm. In glass eels just after metamorphosis, gill lamellae developed from the gill filaments, and a rich population of chloride cells was observed in the gill filaments. In glass eels collected at a coastal area, chloride cells were extensively distributed in the gill filaments. The chloride cell size decreased progressively in glass eels transferred from seawater (SW) to freshwater (FW), whereas there was no difference in cell number. In contrast, some Na⁺,K⁺-ATPase immunoreaction distinct from typical chloride cells was observed in the gill lamellae throughout FW-transferred fish, but disappeared in control fish maintained in SW for 14 days. These findings indicate that the gill and gill chloride cells developed slowly during the extremely long larval stage, followed by rapid differentiation during a short period of metamorphosis. The excellent euryhalinity of glass eels may be due to the presence of the filament chloride cells and lamellar Na⁺,K⁺-ATPase-immunoreaction, presumably being responsible for SW and FW adaptation, respectively.     

Branchial and intestinal osmoregulatory acclimation in the four-eyed sleeper, <Emphasis Type="Italic">Bostrychus sinensis</Emphasis> (Lacepède), exposed to seawater

Bostrychus sinensis is a facultative air breather that inhabits waters of a wide range of salinities. This study aimed to elucidate whether branchial and intestinal osmoregulatory acclimation occurred in B. sinensis transferred from 5‰ water through a progressive increase in salinities to seawater. Our results indicate that B. sinensis acted as a hyperosmotic regulator in 5‰ water, but exhibited hypoosmotic hypoionic regulation in seawater. During short- (1 day) and medium- (10 days) term acclimation to seawater, there were only minor perturbations in plasma osmolality and [Na⁺], which returned to control levels after 45 days of exposure to seawater. Branchial Na⁺/K⁺-ATPase activity was unaffected by 1, 10 or 45 days of exposure to seawater. However, prolonged (45 days) acclimation to seawater led to a significant increase in Na⁺/K⁺-ATPase α-subunit protein abundance. Taken together, these results indicate that there could be changes in the expression of Na⁺/K⁺-ATPase isoforms and/or post-translational modification of Na⁺/K⁺-ATPase in the gills of fish exposed to seawater. Immunofluorescence microscopy revealed that acclimation to seawater for 10 days only resulted in no change in branchial Na⁺/K⁺-ATPase protein expression, but there were increases in protein expression of cystic fibrosis transmembrane regulator (CFTR)-like chloride channel and Na⁺:K⁺:2Cl⁻ cotransporter (NKCC; probably NKCC1). Indeed, NKCC was undetectable in gills of fish kept in 5‰ water by Western blotting, but it became weakly detectable in fish exposed to seawater for 10 days and prominently expressed in fish exposed to seawater for 45 days. Therefore, our results indicate that branchial CFTR-like chloride channel and NKCC1 were the determining factors in the transition between hyperosmotic regulation and hypoosmotic hypoionic regulation in B. sinensis. Furthermore, the intestine of B. sinensis also served as an important osmoregulatory organ, since there were significant increases in both the activity and protein abundance of intestinal Na⁺/K⁺-ATPase in fish acclimated to seawater for 45 days. The effectiveness of branchial and intestinal osmoregulatory acclimation in B. sinensis during seawater acclimation led to only a minor increase in plasma osmolality, and thus resulted in relatively unchanged free amino acid contents in muscle and liver.     

Osmotic and ionic concentration of the egg capsule fluid of Crepidula fornicata in relation to embryonic development

Osmotic pressure and major ions (Cl⁻, Na⁺, Mg²⁺, Ca²⁺) of the egg capsule fluid in the slipper limpet Crepidula fornicata were investigated in relation to embryonic development. Calcium permeability of the capsule wall was studied at oviposition, by dipping freshly laid egg capsules in ⁴⁵Ca as a tracer. This study also determined total calcium content of the embryos at different developmental stages. Osmolarity and major ion concentrations in egg capsule fluid were higher than seawater at uncleaved and trochophore stages, and then dropped to the same level as sea water at veliger stage. Concentrations of Cl⁻ and Na⁺ were relatively high at oviposition, peaked at trochophore stage, and finally dropped close to concentrations of seawater at hatching. In contrast, concentrations of Mg²⁺ and Ca²⁺ decreased steadily during capsular development. Radiotracer permeability experiments in freshly laid egg capsules confirmed that the capsule wall is impermeable to this ion at that stage. However, because of the dissolution of the inner layer of the wall during the final part of capsular development, the wall becomes permeable to calcium and probably to the rest of the major ions studied.     

Geochemistry and quality of groundwater of the Yarmouk basin aquifer,north Jordan

Quality of groundwater in the Yarmouk basin, Jordan has been assessed through the study of hydrogeochemical characteristics and the water chemistry as it is considered the main source for drinking and agriculture activities in the region. The results of the relationship between Ca²⁺ + Mg²⁺ versus HCO₃^? + CO₃^2?, Ca²⁺ + Mg²⁺ versus total cations, Na⁺ + K⁺ versus total cations, Cl^? + SO₄^2? versus Na⁺ + K⁺, Na⁺ versus Cl^?, Na⁺ versus HCO₃^? + CO₃^2?, Na⁺ versus Ca²⁺, and Na⁺: Cl^? versus EC describe the mineral dissolution mechanism through the strong relationship between water with rocks in alkaline conditions with the release of Ca²⁺, Mg²⁺, Na⁺, K⁺, HCO₃^?, CO₃^2?, SO₄^2?, and F^? ions in the groundwater for enrichment. Furthermore, evaporation processes, groundwater depletion, and ion exchange contribute to the increased concentration of Na⁺ and Cl^? ions in groundwater. Anthropogenic sources are one of the main reasons for contamination of groundwater in the study area and for increasing the concentration of Mg²⁺, Na⁺, Cl^?, SO₄^2?, and NO₃^? ions. Results show the quality of groundwater in the study area is categorized as follows: HCO₃^? + CO₃^2? > Cl^? > SO₄^2? > NO₃^? > F^? and Na⁺ > Ca²⁺ > Mg²⁺ > K⁺. In conclusion, the results of TDS, TH, and chemical composition showed that 26% of the groundwater samples were unsuitable for drinking. About 28% of groundwater samples in the study area have a high concentration of Mg²⁺, Na⁺, and NO₃^? above the acceptable limit. Also, based on high SAR, 10% of the groundwater samples were not suitable for irrigation purposes.     

Ecophysiology of Limonium axillare and Avicennia marina from the coastline of Arabian Gulf-Qatar

Attention is being focused on the coastline from Doha to Ras Laffan in Qatar since higher activities in the development of land and establishment of roads, highways and new buildings and houses is not coupled by serious studies on habitat destruction, fragmentation or disturbances. Ecophysiological study was carried out to investigate the adaptation of two halophytes (Limonium axillare and Avicennia marina) in this area, with special emphasis on the ultrastructure of salt glands found in the leaves. Soils in these locations accumulated much Na⁺ and Cl^? as compared to other cations like K⁺, Ca²⁺ and Mg²⁺. Both plants accumulated higher concentrations of Na⁺ , Cl^?, and Ca²⁺ and lower concentrations of K⁺ and Mg²⁺. Organic compounds found in leaves of these plants under their natural habitats including proline, soluble sugars and nitrogen, and photosynthetic pigments were determined. Scanning electron micrographs of the surface of leaves showed that salt glands of these plants are well developed. It is urgently required that exact vegetation maps, and monitoring exercises will be conducted, in order to document exactly the state of the vegetation in Qatar. Only this will allow the environment authorities to bring forward suggestions for vegetation and ecosystem management to the decision makers.     

Wet deposition chemistry studies at Suva, Fiji, a remote tropical island site in the south Pacific

A field project encompassing wet-only rainwater sampling was initiated as a bilateral Fiji/Australia activity. Normally, biweekly samples were collected, using a wet-only rainwater sampler, and analysed for H⁺, Na⁺, K⁺, Mg²⁺, NH₄ ⁺, Cl^–, NO₃ ^–, SO₄ ^2–, PO₄ ^3-, methane sulphonic acid, oxalic acid, formic acid and acetic acid. The pH of the rainwater ranged between 5.730 and 4.480 with an average value of 5.176, slightly lower than the pH of unpolluted rainwater saturated with atmospheric CO₂(pH = 5.650). Na⁺and Cl^–were the major ions with average concentrations of 98.15 M and 109.57 M respectively. There is an excellent correlation between the cation sum (average 147.71 eq L^-1) and the anion sum (average 142.12 eq L^-1) attesting to the quality of the data generated. This paper presents the detailed results of the study for a relatively clean remote island site in Suva, Fiji, latitude 18° 09 S, longitude 178° 27 E, height 6 m, and outlines prospects for further work.     

Modulation of branchial ion transport protein expression by salinity in glass eels (<Emphasis Type="Italic">Anguilla anguilla</Emphasis> L.)

The Anguillid juvenile glass eel must deal with the osmoregulatory consequences of highly variable environmental salinities on its recruitment migration from coastal to fresh waters. Changes in ionoregulatory parameters and branchial ion transport protein [Na⁺/K⁺-ATPase, Na⁺:K⁺:2Cl⁻ cotransporter (NKCC), cystic fibrosis transmembrane regulator (CFTR) anion channel, V-type proton ATPase] expression (activities, protein and/or mRNA level expression and/or cellular localization) in response to acclimation to a broad range of ionic strengths [distilled water (DW) to hypersaline water (HSW; 150%) sea water (SW 32‰)] was studied. The estuarine glass eels were very euryhaline and successfully acclimated to acute changes in environmental ionic strength from 50% SW, with high mortality only observed in HSW (51%) and sublethal osmoregulatory indicators (whole body water content and sodium levels) disturbed at the extremes (DW and HSW). Central to a high salinity acclimation were elevated branchial Na⁺/K⁺-ATPase, NKCC and CFTR expression. At lower salinity, Na⁺/K⁺-ATPase expression was maintained and NKCC and CFTR expressions were reduced. Branchial chloride cells increased in size up to SW but decreased in HSW. During hypotonic disturbance (DW), no compensatory elevation in V-ATPase or Na⁺/K⁺-ATPase expression was observed.     

Interaction of short-term testosterone treatment with osmotic acclimation in the gilthead sea bream <Emphasis Type="Italic">Sparus auratus</Emphasis>

To assess the interaction between testosterone (T) treatment and acclimation to different salinities, seawater-acclimated gilthead sea bream (Sparus auratus) were implanted with slow-release coconut oil implants alone (control) or containing T (5 μg/g body mass). After 5 days, eight fish of control and T-treated groups were sampled. The same day, eight fish of each group were transferred to low salinity water (LSW, 6 ppt, hypoosmotic test), seawater (SW, 38 ppt, control test) and high salinity water (HSW, 55 ppt, hyperosmotic test) and sampled 9 days later. Gill Na⁺, K⁺-ATPase activity increased in HSW-acclimated fish with respect to SW- and LSW-acclimated fish in both control and T-treated groups. Kidney Na⁺, K⁺-ATPase activity was also enhanced in HSW-acclimated fish, but only in T-treated group. From a metabolic point of view, most of the changes observed can be attributed to the action of salinity and T treatment alone, since few interactions between T treatment and osmotic acclimation to different salinities were observed. Those interactions included in treated fish: in the liver, decreased capacity in using glucose in fish acclimated to extreme salinities; in the gills, decreased capacity in using amino acids in HSW; in the kidneys increased capacity in using amino acids in extreme salinities; and in the brain, decreased glycogen and acetoacetate levels of fish in LSW.     

Salinity effects on glucose uptake and catabolism in the obligately psychrophilic marine bacterium Vibrio marinus

Studies on the effects of various salinities on the uptake and catabolism of glucose in Vibrio marinus MP-1 revealed several significant shifts in total uptake and respiration as the cells were subjected to increasingly greater concentrations of NaCl. As the salinity increased from 0.30 to 1.0 M NaCl, there was a decrease in the C₆/C₁ (CO₂) ratio. The resulting patterns suggests that the relative participation of the hexose monophosphate pathway in glucose catabolism was altered. This pathway is apparently shut down in the region of the minimum-growth salinity, and may be related to growth limitation at rower salinities. The shift in C₆/C₁ ratio was not affected by changing the incubation temperature, nor was it dependent specifically on the presence of Na⁺ or Cl^-. As the salinity increased from 0.15 to 0.30 M NaCl, there was a shift in the total uptake patterns which suggests the formation and loss of metabolic by-products derived from the first, second, sixth, and presumably fifth carbons of glucose.This paper was taken in part from a dissertation by the senior author, submitted in partial fulfillment of the requirement for the Ph.D. degree, Oregon State University, Corvallis. Published as technical paper No. 3647, Oregon Agricultural Experiment Station.     

Physiological role of branchial carbonic anhydrase in the shore crabCarcinus maenas

Excretion of total CO₂ and uptake of sodium and chloride ions across the branchial epithelium of the posterior gills of the shore crabCarcinus maenas, collected from Kiel Bay (Baltic Sea) in 1989, were measured using isolated perfused gill preparations. Total CO₂ effluxes depended on the HCO ₃ ^- concentration of the internal perfusate in a saturable mode and were inhibited by internally and externally applied acetazolamide at 10^–4 M. Potential differences between hemolymph space and medium did not change significantly during experimental treatments. Neither a bicarbonate gradient (6 mM) directed from the internal perfusate to external bath solution nor symmetrically applied 10^–4 M acetazolamide significantly influenced the influxes of Na⁺ and Cl^–. Results confirmed the role of carbonic anhydrase in CO₂ excretion but called into question the assumed functioning of the enzyme in branchial ion transport processes.     

Major osmolyte changes during oocyte hydration of a clupeocephalan marine benthophil: Atlantic herring (<Emphasis Type="Italic">Clupea harengus</Emphasis>)

The major inorganic and organic osmolytes responsible for hydrating the oocytes during pre-ovulatory meiotic maturation in autumn- and spring-spawning stocks of Atlantic herring are examined. Despite the ovulated eggs of spring-spawning herring being 1.6- to 2-fold larger than the autumn-spawning stock, the GSI (27 ± 3%) and degree of oocyte hydration (70–72% water) were similar. Normalising the data with respect to dry mass revealed that the physiological mechanisms underlying the maturational influx of water were the same for both classes of egg. Cl⁻, K⁺ and P_i together with a small pool of free amino acids (FAA) represented the driving forces for oocyte hydration. K⁺ (autumn and spring) and P_i (spring) maintained their concentrations in the ovulated eggs, while all other ions, including Cl⁻, Na⁺, NH₄ ⁺ and Mg²⁺ were significantly diluted. In contrast the FAA concentration increased during the hydration process. Amongst the inorganic ions, Cl⁻ showed the greatest increase in the ovulated eggs. The FAA content doubled from 1.5 to 3.3% of dry mass during oocyte hydration and accounted for 29% of the calculated ovoplasmic osmolality in the ovulated eggs from both autumn- and spring-spawners. This significant osmotic effect of the small pool of FAA was due to the low water content of the benthic eggs. The differential movement of the inorganic and organic osmolytes that underly oocyte hydration in Atlantic herring are discussed in relation to current models of transmembrane ion flux.