Ionoregulatory and respiratory responses of brown trout,Salmo trutta,exposed to lethal and sublethal aluminium in acidic soft waters

Soft water acclimated (Ca²⁺ 0.02 mM; Na⁺ 0.03 mM; K⁺ 0.01 mM; pH 7.0), cannulated brown trout (Salmo trutta) were exposed to various pH and aluminium (Al) regimes (pH 7.0, pH 5.0, pH 5.0 plus Al: 50, 25, and 12.5 g l^–1) for up to 5 days in order to determine (i) the sublethal concentration of Al at pH 5.0 for this species (ii) their ionoregulatory and respiratory status. No mortality or physiological disturbances were evident at pH 7.0 or pH 5.0. All trout died within 48 h at pH 5.0 in the presence of Al at 50 g l^–1 and 67% died over the 5 day period at pH 5.0 in the presence of Al at 25 g l^–1. Fish at these lethal Al concentrations showed significant decreases in arterial blood oxygen content (C_aO₂) but no changes in plasma osmolarity or the concentrations of plasma Na⁺, K⁺ and Cl^–. Physiological disturbance was more marked at the 50 g l^–1 Al concentration. The surviving fish at 25 g l^–1 showed few signs of physiological recovery while continually exposed to this regime. No fish died during the exposure to water of pH 5.0 containing 12.5 g l^–1 Al, but physiological disturbance was still apparent. These sublethally-stressed trout showed a transient decline in the plasma concentrations of Na⁺ and Cl^–1. Although C_aO₂ decreased, recovery was evident. The data suggest that in the brown trout, environmental Al concentration is as important as pH and calcium concentration in determining the physiological status of the fish.     

Effects of sublethal, acidic aluminum exposure on blood ions and metabolites, cardiac output, heart rate, and stroke volume of rainbow trout, Oncorhynchus mykiss

Doppler flow probes were fitted around the ventral aorta of rainbow trout, which were exposed to combinations of pH and aluminum (pH 5.1–6.2, Al 0–80 g l^–1) for 60 h. Fish accumulated Al at the gill and exhibited decreased blood Na⁺, Cl^–, and Ca²⁺ concentrations, and increased K⁺, hematocrit, hemoglobin, glucose, and lactate, indicating increasing ionoregulatory disturbance with increasing Al concentration. Fish exposed to ambient water (6.2) or low-pH (5.3) water without Al exhibited slight reductions in heart rates, as well as increased stroke volume, resulting in little variation in cardiac output. In the presence of Al (20 to 40 g l^–1) at low pH (5.1–5.3), fish increased their heart rate slightly and generally maintained their stroke volume, resulting in increased cardiac output in the first two days of exposure. At the highest Al concentration (80 g l^–1, pH 5.1), tachycardia was observed, concomitant with a decrease in stroke volume. The ionoregulatory imbalance and resulting increased blood viscosity explain these increases in heart rate rather than stroke volume in fish exposed to high concentrations of Al.     

The effects of elevated winter temperature and sub-lethal pollutants (low pH, elevated ammonia) on protein turnover in the gill and liver of rainbow trout (Oncorhynchus mykiss)

Appetite, growth, and protein turnover (synthesis, growth and degradation) of liver and gills were measured in juvenile rainbow trout (Oncorhynchus mykiss) fed to satiation, and exposed for 90 days to elevated winter temperatures (+2 °C above ambient) and either low pH (5.2) in softwater or 70 M total ammonia (TAmm) in hardwater. All fish increased in weight during the experiments, but those exposed to +2°C grew significantly more than those at ambient temperature due to a stimulation of appetite. During the relatively constant temperature of the first 75 days, +2 °C caused a significant increase in the rates of protein synthesis and degradation in the liver of hardwater-acclimated fish, as a result of an increase in RNA translational efficiency (KRNA). The elevated temperature also induced an increase in gill protein synthesis in softwater-acclimated fish but in this case the underlying mechanism was an increase in Cs, the capacity for protein synthesis (RNA:protein) rather than in KRNA. The addition of 70 M TAmm had no effect on protein turnover in either liver or gills of hardwater-acclimated fish. Low pH inhibited protein growth in the liver of softwater-acclimated fish at day 90 under both temperature regimes. This inhibition was effected via a decrease in protein synthesis at control temperature but via an increase in protein degradation when the fish were exposed to both low pH and +2 °C. From these results we conclude that a simulated global warming scenario has potentially beneficial rather than detrimental effects on protein turnover and growth of freshwater fish during winter.     

Influence of gonadotropic hormone-releasing hormone analog (GnRH-A) on plasma sex steroid profiles and milt production in male winter flounder,Pseudopleuronectes americanus (Walbaum)

The effects of gonadotropic hormone-releasing hormone analog (GnRH-A) treatment on the onset and duration of increases in plasma sex steroids and milt production (milt volume and number of spermatozoa) were investigated in prespawning male winter flounder. After treatment of maturing males during the winter with a single injection of either 20 or 200 g/kg [D-Ala⁶, Pro⁹-NHEt]LHRH (GnRH-A), plasma levels of testosterone and 11-ketotestosterone were increased within 12h and the steroid hormone levels remained elevated for long periods lasting several days. The androgenic steroid response of males was delayed after the administration of a lower dose of GnRH-A (2 g/kg). Although a single GnRH-A injection in December or January advanced the onset of spermiation in some males, only small amounts (<50 l) of milt could be collected. By March, all males were in spermiating condition following GnRH-A treatment; however, significant increases in sperm production, particularly increases in milt volume, occurred in fish twice treated with GnRH-A.Part of this work presented at the First Symposium of Fish Endocrinology, Edmonton, Alberta, Canada June 1988 and the Satellite Symposium on Applications of Comparative Endocrinology to Fish Culture, Almuñecar, Granada, Spain May 1989     

17β-Estradiol, but not testosterone stimulates gonadotropin II concentrations in the protandrous black porgy, Acanthopagrus schlegeli Bleeker

The objective of the present study was to investigate the in vivo effects of different doses of 17-estradiol (E₂) and testosterone (T) on the levels of plasma and pituitary gonadotropin II (GTH II) in 2-year-old black porgy, Acanthopagrus schlegeli, during the spawning season. Male fish were distributed among 7 groups (n = 49), control, E₂or T (with 3 doses, 2.4 ng, 72 ng and 2.2 g g^–1 body weight). Fish were injected with the respective vehicle or different doses of E₂ or T on days 1 and 14. Plasma E₂ levels were significantly increased in the 72 ng E₂ group on days 8 and 14. Plasma vitellogenin levels were significantly higher in the 72 ng E₂ group on days 14 and 20, and 2.2 g E₂ group on days 8, 14 and 20 than those in the control group. Plasma GTH II concentrations were significantly higher in the 2.2 g E₂ group than in the control and other E₂groups on days 8, 14 and 20. Pituitary GTH II contents was significantly higher in the 7.2 ng E₂ group compared to the control and other E₂groups on day 20. Plasma GTH II concentrations were similar in the control and all the T groups on days 8, 14 and 20. None of the doses of T treatment stimulated pituitary GTH II content on day 20, although plasma vitellogenin levels were elevated. It is concluded that GTH II synthesis and secretion in black porgy is stimulated by an estrogen-specific effect.     

Quantitation of inert feed ingestion in larval silver sea bream (Sparus sarba) using auto-fluorescence of alginate-based microparticulate diets

The ingestion of an inert feed as a sole food source was investigated in larval silver sea bream (Sparus sarba) fed an alginate-based microparticulate diet. Using the auto-fluorescent properties of pigments associated with the alginate base, ingestion and gut content were investigated over a 6 h experimental period in fed and unfed larvae. By extracting and measuring chlorophyll a (Chl a) and phaeopigment content of feeding larval fish and relating this to standardized Chl a and phaeopigment content of the diet, relative to diet weight, it was determined that individual fed 7-day old larvae had a maximum gut content of 1.05±0.09 g diet while 14-day old fed fish had a maximum gut content of 3.17±0.90 g diet. On average, the gut content of 14-day old fish was 2.89 times greater than the gut content of 7-day old fish. The dry weight of larval sea bream increased from 43±4.2 g at day 7 to 134.3±20.4 g at day 14 indicating that growth of fish fed this inert feed was substantial. Gut pigment dynamics suggested that Chl a was degraded to phaeopigments by 7-day but not 14-day old larvae and the individual gut dietary content varied considerably in 14-day old fish. The maximum Chl a and phaeopigment content in larval sea bream was 0.4 ng ind^–1 and 0.55 ng ind^–1 for 7-day old fish and 1.54 ng ind^–1 and 2.81 ng ind^–1 for 14-day old fish respectively. The present method may potentially allow simple and direct assessment of larval fish feed ingestion in both an experimental and commercial setting.     

The biliary accumulation of corticosteroids in rainbow trout,Oncorhynchus mykiss,during acute and chronic stress

The accumulation of immunoreactive corticosteroids in the bile of rainbow trout during stress was monitored by radioimmunoassay and GUMS. Although plasma cortisol levels were elevated by confinement for 1 hour, biliary levels of free and conjugated steroids in the bile were unaffected. However, after 24 hours confinement, in addition to elevated plasma cortisol levels, free and conjugated steroids in the bile were also significantly higher than in control, unstressed fish. The time-course of change in plasma and biliary corticosteroid levels was determined in rainbow trout subject to 96 hours confinement stress. Free steroid levels in the bile of stressed fish were elevated within 2 hours of the onset of stress, while levels of conjugated steroids were significantly elevated within 4 hours of the onset of confinement. Analysis of bile from stressed fish, by GC/MS, established the major conjugated steroids present to be tetrahydrocortisone (230 g ml^–1 bile), tetrahydrocortisol (75 g ml^–1), cortisone (33.5 g ml^–1), cortisol (25 g ml^–1) and -cortolone (5 g ml^–1). The data are discussed with reference to the role of cortisone and conjugating enzymes in the clearance of cortisol, and further data are presented to suggest that the analysis of biliary steroid content may provide a suitable means of identifying stressed fish under conditions in which an additional sampling stress is unavoidable.     

Stimulation of ureogenesis in the perfused liver of an Indian air-breathing catfish, Clarias batrachus, infused with different concentrations of ammonium chloride

The pattern of changes of activity of the urea cycle enzymes and the rate of urea-N excretion were studied in the perfused liver of an Indian air-breathing ureogenic walking catfish, Clarias batrachus. The liver was perfused with different concentrations of NH₄Cl for a period of 60 min to determine the role of ammonia for stimulation of hepatic ureogenesis and the threshold level of ammonia loading needed to cause such stimulation. Both the urea-N excretion and the ammonia uptake by the perfused liver were found to be a saturable process. Ammonia accumulated significantly in the liver infused with 1.25 moles g liver ^–1 min^–1 of NH₄Cl, followed by a maximum accumulation of about 28.5 moles g wet wt^–1 with the infusion of 5.08 moles g liver^–1 min^–1. The Vmax of the urea-N excretion (0.47 mol g liver^–1 min^–1) was obtained with the addition of 5.08 moles g liver^–1 min^–1 of NH₄Cl. Both the tissue and the specific activity of the urea cycle enzymes, except ornithine transcarbamylase and arginase, were stimulated significantly with the infusion of either 1.25 or 5.08 moles g liver^–1 min^–1 of NH₄Cl. Maximum stimulation of tissue activity of carbamoyl phosphate synthetase (about 120%) was seen with the infusion of 5.08 mol g liver^–1 min^–1, and for argininosuccinate synthetase (about 135%), and argininosuccinate lyase (about 50%) with the infusion of 10.81 mol g liver^–1 min^–1 of NH₄Cl. Higher accumulation of ammonia of about 10–15 mol g wet wt^–1 from the physiological level in the perfused liver while infusing with NH₄Cl was suggested to be one of the major causes of stimulation of ureogenesis. The presence of such physiological adaptive strategy is probably necessary in this unique group of air-breathing walking catfish to survive under hyper-ammonia stress in their normal habitat or while living outside water or while burrowing inside mud.     

Influence of cortisol, growth hormone, insulin-like growth factor I and 3,3′,5-triiodo-l-thyronine on hypoosmoregulatory ability in the euryhaline teleost Fundulus heteroclitus

The capacity of cortisol, ovine growth hormone (oGH), recombinant bovine insulin-like growth factor I (rbIGF-I) and 3,3,5-triiodo-l-thyronine (T₃) to increase hypoosmoregulatory capacity in the euryhaline teleost Fundulus heteroclitus was examined. Fish acclimated to brackish water (BW, 10 ppt salinity) were injected with a single dose of hormone suspended in oil and transferred to seawater (SW, 35 ppt salinity) 10 days post-injection. Fish were sampled 24 h after transfer and plasma osmolality and gill Na⁺, K⁺-ATPase activity were examined. Transfer from BW to SW induced significantly increased plasma osmolality but not gill Na⁺, K⁺-ATPase activity. Cortisol (50 g g^–1 body weight) improved the ability to maintain plasma osmolality and to increase gill Na⁺, K⁺-ATPase activity. oGH (5 g g^–1 body weight) also increased hypoosmoregulatory ability and gill Na⁺, K⁺-ATPase activity. A cooperation between oGH and cortisol was observed in increasing hypoosmoregulatory ability but not in increasing gill Na⁺, K⁺-ATPase activity. rbIGF-I (0.5 g g^–1 body weight) alone was without effect in increasing salinity tolerance or gill Na⁺, K⁺-ATPase activity. rbIGF-I and oGH showed a positive interaction in increasing salinity tolerance, but not gill Na⁺, K⁺-ATPase activity. Treatment with T₃ (5 g g^–1 body weight) alone did not increase salinity tolerance or gill Na⁺, K⁺-ATPase activity, and there was no consistent significant interaction between cortisol and T₃ or between GH and T₃. The results confirm the classical role of cortisol as a seawater-adapting hormone and indicate an interaction between cortisol and the GH/IGF-I axis during seawater acclimation of Fundulus heteroclitus.     

The effects of gonadal development and sex steroids on growth hormone secretion in the male tilapia hybrid (Oreochromis niloticus × O. aureus)

Profiles of plasma growth hormone (GH) in male tilapia hybrid (Oreochromis niloticus x O. aureus) were measured and compared at different times of the year. The profiles did not appear to be repetitive, however, differences in their nature were observed at the different seasons; the most erratic profiles were seen in the height of the reproductive season (July), while the peaks were more subdued in the spring and disappeared in the autumn. Peaks in male fish were more prominent than in the females when measured in July. Perifused pituitary fragments from fish with a high GSI responded to salmon gonadotropin-releasing hormone (sGnRH) analog (10 nM-1 M), while those from fish with a low GSI barely responded to even the highest dose. Exposure of perifused pituitary fragments from sexually-regressed fish to carp growth hormone-releasing hormone (cGHRH; 0.1 M) or sGnRH (I M) stimulated GH release only after injection of the fish with methyl testosterone (MT; 3 injections of 0.4 mg kg ¹). The same MT pretreatment did not alter the response to dopamine (DA; 1 or 10 M). GH pituitary content in MT-treated fish was lower than in control fish, which may be explained by the higher circulating GH levels in these fish, but does not account for the increased response to the releasing hormones. Castration abolished the response of cultured pituitary cells to sGnRH (I fM-100 nM) without altering either their basal rate of secretion or circulating GH levels. Addition of steroids to the culture medium (MT or estradiol at 10 nM for 2 days) enabled a GH response to sGnRH stimulation in cells from sexually regressed fish. Pituitary cells which had not been exposed to steroids failed to respond to sGnRH, although their response to forskolin or TPA was similar to that of steroid-exposed cells. It would appear, therefore, that at least one of the effects of the sex steroids on the response to GnRH is exerted proximally to the formation of cAMP, or PKC, presumably at the level of the receptor. An increase in the number of receptors to the GH-releasing hormones, following steroid exposure, would explain also the changing nature of the GH secretory profile in different stages of the reproductive season.     

Dopamine inhibits gonadotropin secretion in the Chinese loach (Paramisgurnus dabryanus)

The effects of dopamine on gonadotropin (GtH) secretion in sexually mature Chinese loach were investigated. Spontaneous secretion of GtH was inhibited within 1 h following an intramuscular injection of dopamine (100 g/g body wt). Similarly, dopamine (50 and 100 g/g body wt) caused a significant reduction in serum GtH in fish with elevated GtH levels as a result of pretreatment with gonadotropin-releasing hormone (GnRH) analogs either alone or in combination with the dopamine receptor antagonist domperidone. In summary, the present study provides direct evidence that dopamine functions as a gonadotropin-release inhibitory factor in the Chinese loach by blocking spontaneous and GnRH-stimulated GtH release.     

Dehydration is more effective for the control of embryonic development and larval hatching of Diplectanum aequans (Monogenea, Diplectanidae) than formalin and trichlorphon

Embryonic development and larval hatching of the monogenean Diplectanum aequans, gill parasite of sea bass Dicentrarchus labrax, was studied in relation to different prophylactic treatments. Groups of eggs of D. aequans were submitted to different in vitro treatments: formalin (300 and 100 L L^–1 per 1 hour), Neguvon^® (trichlorphon 0.2 mg L^–1 per 48 hours) and dehydration for 4 and 8 hours. Percentages of hatched larvae, aborted larvae and undeveloped embryos were estimated in comparison with the control group. Results showed that 300 L L^–1 formalin and dehydration treatments were able to reduce larval hatching significantly, while Neguvon^® and 100 L L^–1 formalin treatments had no effect.     

The effect of photoperiod, tank colour and light intensity on growth of larval haddock

In two separate experiments, haddock (Melanogrammus aeglefinus) larvae were raised under different photoperiods (24L : 0D or 15L : 9D), or different combinations of tank colour (black or white) and light intensity (1.1 mol s^–1 m^–2 or 18 mol s^–1 m^–2). Growth (0.8% day^–1 in standard length; 2.9% day^–1 in body area) and survival (2%) were not significantly different between photoperiod treatments after 35 days. Larval survival was greater in white versus black tanks after 41 days (2% versus l%, respectively). Growth of larvae was impaired in black tanks at low (1.1 mol s^–1 m^–2) light intensity (0.8% day^–1 in standard length and 2.2% day^–1 in body area versus 1.1% day 21 in standard length and 3.1% day^–1 in body area, for all other treatments). Transmission and reflection of light was low in black tanks at low incident light, and there was very little upwelling light. The resultant poor prey to background contrast probably resulted in larvae being unable to consume sufficient food to sustain a level of growth comparable to that in other treatments.     

Characterization of growth hormone binding sites in the goldfish,Carassius auratus: effects of hypophysectomy and hormone injection

A recombinant carp growth hormone (rcGH) was used to develop for a GH radioreceptor binding assay in the goldfish (Carassius auratus). Specific binding of¹²⁵I-rcGH to goldfish liver membranes was a pH, time, temperature, and membrane protein dependent process. Scatchard and LIGAND analysis indicated a single class of high affinity and low capacity binding site, with an association constant (Ka) of 1.9×10¹⁰ M^–1 and a maximum binding capacity (B_max) of 9 fmol mg^–1 protein. Liver tissue displayed the highest¹²⁵I-rcGH binding of all the tissues examined. Displacement of¹²⁵I-rcGH with various unlabeled teleost and mammalian GHs and prolactins revealed that the goldfish hepatic binding site was highly specific for teleost GH. Intraperitoneal administration of 0.1, 1.0, and 10 g rcGH g^–1 body weight to hypophysectomized goldfish resulted in a 27, 52, and 68% decrease in total binding sites, respectively. Injection of a high dose of rat prolactin (rPRL) (5 g rPRL g^–1 body weight) also resulted in a 32% decrease in total binding sites. These results suggest that endogenous GH may have a role in the regulation of its own receptors in the goldfish.     

Whole animal transepithelial potential (TEP) of coho salmon during the parr-smolt transformation and effects of thyroxine,prolactin and hypophysectomy

Whole animal transepithelial potentials (TEP) of yearling coho salmon (Oncorhynchus kisutch) in fresh water and after transfer to seawater were recorded throughout parr-smolt transformation (smoltification) from February to August 1984, along with plasma Na⁺ and Cl^– concentrations and osmolality. Based on plasma ion regulation in seawater, the yearling coho in this study completed smoltification and attained sea-water adaptability in April. TEP in freshwater fish decreased (became inside-negative) after smoltification, and the TEP increased significantly (P < 0.01) after seawater transfer. When fish were transferred into seawater, thyroxine increased TEP of the transferred smolts by approximately 30% over the control level (P < 0.01) in April, but this did not occur when freshwater postsmolts were transferred in July and August. Hypophysectomy increased TEP (P < 0.01) in fresh water; it did not affect the TEP of the fish after seawater transfer. Ovine prolactin (3 g/g body weight) implanted into seawater-adapted fish caused a reduction in TEP (P < 0.01) when fish were exposed to fresh water. Whole-animal TEP appears to provide a valuable index of the completion of smoltification (April–May) and a useful tool for investigating the endocrine control of salmonid osmoregulation.     

In vivo activity of salmon gonadotropin releasing hormone (GnRH), its agonists with structural modifications at positions 6 and 9, mammalian GnRH agonists and native cGnRH-II on the spawning of an Indian catfish

Effects of the native GnRHs and various agonists have been evaluated on the spawning of an Indian catfish, Heteropneustes fossilis. This study tested salmon (s) GnRH agonists and mammalian (m) GnRH agonists where a D-amino acid residue was substituted alone at position 6 or the C-terminal was modified with ethylamide. GnRH agonists with a combination of these structural modifications were also evaluated separately for their effect on the spawning of the catfish. Native sGnRH, [Pro⁹ NEt]-sGnRH agonist and chicken (c) GnRH-II exhibited similar activity and induced spawning within 14–18 h at a dose of 100 g kg^–1 body weight (BW). [D-Lys⁶]-sGnRH agonist and [D-Lys⁶ Pro⁹ NEt]-sGnRH agonist, induced spawning at a dose of 100 g kg^–1 BW and 1 g kg^–1 BW, respectively. The most notable observation in this study was the ineffectiveness of [D-Ala⁶]-mGnRH agonist and [Des Gly¹⁰ D-Ala⁶ Pro⁹ NEt]-mGnRH agonist. The results obtained suggest that substitution at position 6 alone, and in conjunction with an ethylamide-based modification at the C-terminal in the native sGnRH structure, increases the potency of the tested agonists to induce spawning in the catfish. This study also discusses the potential use and incorporation of cGnRH-II for the development of more generic spawning induction therapies.     

Relationship between metabolic rate in vitro and body mass in a marine teleost,porgy Pagrus major

The rate of oxygen consumption of minced whole body was determined volumetrically, as an indication of metabolic rate in vitro (M _{in vitro} ), at 20°C in porgy Pagrus major ranging from 0.0002 g (just after hatch) to 2.9 g (67 days old) in body mass. A triphasic relationship was found between M _{in vitro} of individual fish (l.min^–1) and wet body mass W (g). During the prolarval stage accompanied with the transitional period to the postlarval stage (0.00020–0.00023 g, 0–6 days old), the mass-specific metabolic rate in vitro (M _{in vitro} /W in l.g^–1.min^–1) increased with age (D in days) as expressed by an equation M _{in vitro} /W = 3.88 + 0.74/D. During the postlarval stage (0.00031–0.003 g, 8–22 days old), M _{in vitro} /W remained almost constant, independent of body mass following an equation M _{in vitro} /W = 5.24 W^–0.085. During the juvenile and adolescent stages (0.0047–2.9 g, 30–67 days old), M _{in vitro} /W decreased with increasing body mass following an equation M _{in vitro} /W = 1.66 W^–0.235. These results correspond with the triphasic relationship between metabolism in vivo and body mass observed in intact porgy of 0.0002–270 g (Oikawa et al. 1991). It is concluded, therefore, that the dependence of mass-specific metabolic rate on body size exists in vitro as well as in vivo, during the early stages in the porgy. Based on these results, factors controlling the metabolism-size relationship are discussed.     

The relationship between `deep-hole' mitochondria-rich cells and salinity adaptation in the euryhaline teleost, Oreochromis mossambicus

The present study elucidates the relationship between deep-hole MR cells (Lee et al. 1996) and salinity adaptation in tilapia (Oreochromis mossambicus). Freshwater tilapia were transferred to salt water of various salinities, i.e., 5 (hypotonic), 10 (isotonic), 20 (hypertonic), and 30 (hypertonic), for 2 weeks. The density of MR cells, protein content, activity, and localization of the sodium pump were examined. There was no significant difference in serum osmolarity and Na⁺, K⁺, Cl^– levels in fish of the various treatment groups. The amounts of protein and activity of Na,K-ATPase were elevated in fish from SW with the highest salinity. MR cells observed by scanning electron microscope revealed small pits (0.5–1.0 m in diameter) in groups from hypotonic and isotonic water and large crypts (2.4–3.8 m in diameter) in fish from hypertonic water. Moreover, the density of these deep-hole MR cells increased significantly in fish adapted to hypertonic SW. Larger and more numerous deep-hole MR cells of euryhaline tilapia may account for higher protein amounts and activities of Na,K-ATPase, probably to meet the physiological demand of euryhaline teleosts engaged in hyporegulation.     

Effects of sulfide on K+ flux pathways in red blood cells of crucian carp and rainbow trout

The effect of sulfide on K⁺ influx pathways was measured in red blood cells (RBCs) of sulfide-sensitive rainbow trout (Oncorhynchus mykiss) and sulfide-tolerant crucian carp (Carassius carassius). In trout RBCs, maximal inhibition of Na⁺, K⁺-ATPase was attained at 10 mol l^–1 sulfide and amounted to 32% without being influenced by pH between 6.7 and 8.3. Ouabain-resistant K⁺ influx in the absence and presence of sulfide was insignificant at pH values between 6.7 and 7.7. At higher pH values ouabain-resistant K⁺ influx increased, but was inhibited to about 15% by 30 mol l^–1 sulfide. In RBCs of crucian carp neither Na⁺, K⁺-ATPase nor ouabain-resistant K⁺ influx were affected by sulfide concentrations up to 850 mol l^–1. Differences in sulfide-sensitivity of K⁺ influx between both species can be based upon different properties of the membrane transporter themselves. The reduced Na⁺, K⁺-ATPase activity in trout RBCs may also result from a slightly reduced (by 9%) ATP level after sulfide exposure. In addition, intracellular sulfide concentrations were higher in trout RBCs as compared to crucian carp. In trout, intracellular sulfide concentrations reached extracellular levels within 5 min of incubation whereas sulfide concentrations in crucian carp RBCs remained about 2-fold lower than extracellular concentrations. Although the physiological basis of sulfide-insensitive K⁺ influx in crucian carp RBCs is currently unknown it may contribute to the extremely high sulfide-tolerance of this species.