Seawater-adapted Rainbow Trout Research Articles

Experimental exposure of rainbow trout Oncorhynchus mykiss (Walbaum) to the infective stages of the sea louseLepeophtheirus salmonis (Krøyer) influences the physiological response to an acute stressor

The influence of infection with the juvenile stages of the sea louse, Lepeophtheirus salmonis (Krøyer) on the response of rainbow trout Oncorhynchus mykiss (Walbaum) to a net confinement protocol was investigated. The experiment consisted of two groups of seawater-adapted rainbow trout, one which was exposed to a total of 4000 nauplii/copepodid stages of L. salmonis 30, 25 and 14 days prior to confinement. Confinement elicited a greater stress response in the lice-exposed fish, than in the controls, as seen by higher plasma cortisol and glucose levels. A reduced spleen somatic index in exposed fish following 6h confinement coincided with increased erythrocyte and lymphocyte numbers in the blood. Circulating lymphocyte numbers were significantly reduced in both groups 24h post-confinement, when a lower alternative complement activity was recorded in control fish. Prior to confinement, lice-exposed fish had an elevated serum lysozyme activity and reduced oxygen radical production by blood leukocytes. Following confinement, lysozyme activity was gradually reduced in lice-exposed trout. During confinement, oxygen radical production decreased in control fish and increased in infested fish. Overall, transient exposure to juvenile lice altered the response to a second stressor, which has implications for management procedures of L. salmonis exposed fish.

A comparative study of antioxidant enzyme activities in freshwater and seawater-adapted rainbow trout

Comparative studies were performed on the antioxidant enzyme activities and thiobarbituric acid reactive substance (TBARS) concentration in liver and red cells of two groups of rainbow trout (Oncorhynchus mykiss). The fish of the first group were cultured in freshwater and the others were adapted to sea-water by by being transferred from freshwater at 5-6 months of age. Catalase (CAT), glutathione peroxidase (GPX), and glutathione S-transferase (GST) activities were significantly higher in hepatic and extrahepatic tissues in both of the fish groups. Superoxide dismutase (SOD) activities were found lower in the seawater-adapted trout than in the freshwater-cultured trout. In both tissues, TBARS were found significantly higher in the seawater-adapted trout than in the freshwater trout. It was also observed that the red cells of the seawater-adapted trout were much more resistant to oxidative stress than the red cells of the freshwater-cultured trout. The results implicate that antioxidant capacities in the seawater-adapted trout and freshwater trout may be related to physical and chemical characteristics of the environment.

Intestinal base excretion in the seawater-adapted rainbow trout: a role in acid-base balance?

A potential role for the intestine of seawater-adapted teleosts in acid­base regulation was investigated following earlier reports of highly alkaline rectal fluids in the gulf toadfish Opsanus beta. Rectal samples taken from starved seawater-adapted rainbow trout had a high fluid pH (8.90±0.03; mean ± s.e.m., N=13) and base (HCO3-+2CO32-) content of 157±26 mequiv kg-1 (N=11). In trout fitted with rectal catheters, rectal fluid was voided at a rate of 0.47±0.11 ml kg-1 h-1 (N=8), giving a net base excretion rate of 114±15 µequiv kg-1 h-1 (N=7). Drinking rates averaged 3.12±0.48 ml kg-1 h-1 (N=8), and accounted for only 6 % of the base excreted via the intestine, indicating substantial net transport of endogenously derived base into the intestine. Rectally excreted base was approximately balanced by an equivalent efflux of net acid from non-rectal sources (possibly as NH4+ excretion via the gills). Samples taken from four sites along the intestine revealed that the most anterior region (the pyloric intestine) was responsible for the majority of HCO3-+2CO32- accumulation. The pyloric intestine was subsequently perfused in situ to investigate possible mechanisms of base secretion. Net base fluxes were found to be dependent on luminal Cl-, 76 % stimulated by amiloride, 20 % inhibited by 10(-4) mol l-1 acetazolamide, but unaffected by either 10(-4) mol l-1 SITS or 2x10(-5) mol l-1 DIDS. This suggests that the mechanism of base secretion within the pyloric intestine may involve a Cl-/HCO3--ATPase. It is speculated that intestinal base secretion may play a role in facilitating osmoregulation of seawater-adapted teleosts.

Consequences of catecholamine release on ventilation and blood oxygen transport during hypoxia and hypercapnia in an elasmobranch Squalus acanthias and a teleost Oncorhynchus mykiss

The marine dogfish (Squalus acanthias) and the seawater-adapted rainbow trout (Oncorhynchus mykiss) were exposed to acute environmental hypercapnia or hypoxia to evaluate (i) the dynamics of catecholamine release into the circulation and (ii) the impact of catecholamine release on gill ventilation and blood oxygen transport. This comparison was undertaken to test the hypothesis that the pattern and consequences of catecholamine release differ in the two species according to the presence or absence of a Root effect and a red blood cell (rbc) ss-adrenergic response. Hypercapnia and hypoxia elicited marked increases in plasma catecholamine levels in the trout but not in the dogfish. In the trout, catecholamine release occurred abruptly during hypoxia when arterial PO2 (PaO2) decreased below 2.7 kPa. In the dogfish, plasma catecholamine levels remained stable during hypoxia even when PaO2 fell below 2.0 kPa. Trout and dogfish displayed pronounced hyperventilatory responses during both hypercapnia and hypoxia. In trout, the hyperventilatory response consisted of an increase in ventilation amplitude (estimated by opercular cavity pressure changes) with no change in ventilation frequency (fv), whereas in the dogfish, both amplitude (estimated by spiracular cavity pressure changes) and fv increased significantly. The use of an extracorporeal circulation and frequent blood sampling demonstrated that plasma catecholamine levels and ventilation amplitude were not correlated during hypoxia in either species. During hypercapnia in trout, the bolus injection of a catecholamine cocktail (final nominal circulating levels 200 nmol l-1 adrenaline, 50 nmol l-1 noradrenaline) caused a rapid (within 2 min) 33 % reduction in ventilation amplitude that persisted for 3 min; fv was unaffected. This hypoventilatory response occurred concurrently with activation of rbc Na+/H+ exchange and an increase in arterial blood O2 content (CaO2) and O2 specifically bound to haemoglobin (O2/Hb). During hypoxia in trout, a similar injection of catecholamines activated rbc Na+/H+ exchange and increased O2/Hb yet was without effect on ventilation amplitude or fv. In dogfish during hypercapnia or hypoxia, injection of a catecholamine cocktail (final nominal circulating levels 125 nmol l-1 adrenaline, 125 nmol l-1 noradrenaline) caused slight but significant reductions in fv (3-4 min-1) without affecting ventilation amplitude. Catecholamine injections did not affect blood oxygen transport in dogfish. The results demonstrate significant differences in the nature of catecholamine release in dogfish and trout that may reflect, in part, the absence of a Root effect and rbc adrenergic Na+/H+ exchange in the elasmobranch. The present data do not support the hypothesis that circulating catecholamines play a major role in controlling breathing during hypoxia or hypercapnia.

IMMUNOLOCALIZATION OF H+-ATPase IN THE GILL EPITHELIA OF RAINBOW TROUT

The localization of proton pumps (H+-ATPase) in gill epithelia of rainbow trout [Oncorhynchus mykiss (Walbaum)] was elucidated by immunofluorescence microscopy, using rabbit polyclonal antibodies against the 70 kDa subunit of H+-ATPase purified from clathrin-coated vesicles of bovine brain. In the gill epithelia of freshwater trout, the immunostaining was uniformly distributed along the lamellae and generally concentrated in apical regions. It is concluded, therefore, that H+-ATPase is located in the apex of both chloride cells and epithelial cells of freshwater fish. Hypercapnic treatment resulted in a non-polarized and restrictive distribution of H+-ATPase in the chloride cell. No fluorescent staining was observed in the gill epithelium of seawater-adapted rainbow trout, except in some unidentified anucleate surface material. The presence of the 70 kDa subunit in fish gill epithelia was confirmed by Western blot. These results support the proposed role of a proton pump in sodium uptake in freshwater fish and demonstrate that the H+-ATPase in fish gills is of the vacuolar type, antigenically similar to the H+-ATPase in mammalian brain and kidney.

Characterisation of Angiotensin II Binding to Glomeruli from Rainbow Trout Oncorhynchus mykiss Adapted to Fresh Water and Seawater

Specific binding of 1251-[Asn1, Val5]-angiotensin II to isolated glomeruli of freshwater-adapted and seawater-adapted rainbow trout, Oncorhynchus mykiss, reached a plateau after 20 min at 10° and was displaced by nonradiolabelled [Asn1, Val5]-angiotensin II. Seawater adaptation increased the rate of dissociation of 1251-[Asn1, Val5]-angiotensin II from putative receptors. Competitive binding experiments revealed a single population of high-affinity receptors with a KD 0.3-0.4 × 10-10M, which was unchanged by seawater adaptation. Seawater adaptation did, however, reduce the density (Bmax) of the binding sites, which may reflect down-regulation by the higher plasma concentration of angiotensin II in seawater-adapted trout.

Interspecies differences in tissue distribution of 2,3,7,8-tetrachlorodibenzo-p-dioxin between cod ( Gadus morhua) and rainbow trout ( Oncorhynchus mykiss)

The tissue distribution after administration of a single oral dose (30 μg/kg b.wt., corresponding to 12 μCi/kg b.wt.) of 14C-2,3,7,8-dibenzo-p-dioxin ( 14C-2,3,7,8-TCDD) was studied in cod ( Gadus morhua) and sea-water adapted rainbow trout ( Oncorhynchus mykiss) by means of whole-body autoradiography and liquid scintillation counting. Substantial inter-species differences in the distribution pattern were observed. The highest concentrations of 14C-2,3,7,8-TCDD derived radioactivity in the cod were found in the liver and the central nervous system, while the predilection sites for radioactivity in the rainbow trout were the visceral and extravisceral fat depots. The amounts of radioactivity in the liver and the central nervous system of the cod exceeded those of the rainbow trout by a factor of 10 and 7, respectively.

Prostaglandins in the kidney, urinary bladder and gills of the rainbow trout and European eel adapted to fresh water and seawater

Prostaglandins in kidney, gills, and urinary bladder of freshwater-adapted and seawater-adapted rainbow trout, Oncorhynchus mykiss (= Salmo gairdneri), and European eel, Anguilla anguilla, were determined by solid-phase extraction of tissue homogenates and high-pressure liquid chromatography. Prostaglandins E 2, E 1, F 1α, F 2α, and D 2 and the more stable metabolite of prostacyclin, 6-keto F 1α, occurred in these osmoregulatory tissues. In gill filaments and kidneys of both eel and trout, prostaglandins D 2 and 6-keto F 1α were major prostaglandins. Concentrations of these prostaglandins were significantly lower in the eel after seawater adaptation, but not in the trout. The urinary bladder of the trout contained the highest levels of prostaglandins; bladders of seawater-adapted trout contained prostaglandin D 2 at 6.7 ng/mg wet tissue, the highest level of any prostaglandin determined in the present studies. Prostaglandin D 2 was not detected in bladders of freshwater-adapted trout.

White Muscle Intracellular Acid–Base and Lactate Status Following Exhaustive Exercise: A Comparison Between Freshwater- and Seawater-Adapted Rainbow Trout

ABSTRACTThe intracellular acid-base status of white muscle of freshwater (FW) and seawater (SW) -adapted rainbow trout was examined before and after exhaustive exercise.Exhaustive exercise resulted in a pronounced intracellular acidosis with a greater pH drop in SW (0.82 pH units) than in FW (0.66 pH units) trout; this was accompanied by a marked rise in intracellular lactate levels, with more pronounced increases occurring in SW (54.4 mmol 1−1) than in FW (45.7 mmol 1−1) trout. Despite the more severe acidosis, recovery was faster in the SW animals, as indicated by a more rapid clearance of metabolic H+ and lactate loads.Compartmental analysis of the distribution of metabolic H+ and lactate loads showed that the more rapid recovery of pH in SW trout could be due to (1) their greater facility for excreting H+ equivalents to the environmental water [e.g. 15.5% (SW) vs 5.0% (FW) of the initial H+ load was stored in external water at 250min post-exercise] and, to a greater extent, (2) the more rapid removal of H+, facilitated via lactate metabolism in situ (white muscle) and/or the Cori cycle (e.g. heart, liver). The slower pH recovery in FW trout may also be due in part to greater production of an ‘unmeasured acid’ [maximum approx. 8.5 mmol kg−1 fish (FW) vs approx. 6 mmol kg−1 fish (SW) at 70–130 min post-exercise] during the recovery period. Furthermore, the analysis revealed that H+-consuming metabolism is quantitatively the most important mechanism for the correction of an endogenously originating acidosis, and that extracellular pH normalization gains priority over intracellular pH regulation during recovery of acid-base status following exhaustive exercise.

Recovery of Chloride Uptake in Sea Wateradapted Rainbow Trout (Salmo Gairdneri) after Transfer to Fresh Water

ABSTRACT The ability of rainbow trout (Salmo gairdneri Richardson) to acclimate to sea water or partially diluted sea water has been studied many times (Houston, 1959; Parry, 1960; Eddy and Bath, 1979; Prunet and Boeuf, 1985). However, the reverse transition from sea water (SW) to fresh water (FW) has been less well studied. The transition from a hyperosmotic medium to a hypo-osmotic medium reverses the burden on the osmoregulatory organs, i.e. the gills and the kidney. SW teleost fish normally show net salt (NaCl) efflux, whereas FW fish need to acquire salt from the medium. Recent work on salmon (Salmo salar) transferred from SW to FW (Talbot and Potts, 1989; Talbot et al. 1989; Potts et al. 1989) has described the changes in sodium balance, osmoregulation and renal function in adult and juvenile fish. Potts et al. (1985) showed that salmon are capable of taking up sodium immediately on transfer to FW. Chloride uptake via the gills of FW fish is of equal importance to sodium uptake, and the two ions are thought to be transported independently (Maetz and Garcia-Romeu, 1964). This paper examines the changes in chloride transport that occur during the transition from SW to FW.

Adrenergic Regulation of Blood Acid-Base Status following Exhaustive Exercise in Seawater-Adapted Rainbow Trout, Salmo gairdneri

Isoproterenol (β adrenoceptor agonist), propranolol (β adrenoceptor antagonist), or saline (sham) was administered to seawater-adapted rainbow trout immediately after exhaustive exercise in order to assess the role of β-adrenoceptor stimulation in the correction of postexercise blood acid-base disturbances. Exhaustive exercise induced a severe blood acidosis of respiratory and metabolic origin. Recovery from the acidosis was inhibited by β -blockade and facilitated by β-agonist addition. βblockade caused a reduction in branchial H⁺ equivalent excretion to the environmental water and a comparatively large and enduring respiratory acidosis. These likely arose as a result of an inhibition of branchial ion exchanges or through decreases in branchial ventilation, gill blood perfusion, and/or gill membrane permeability. Relative to the control fish, addition of a β-agonist caused no additional change in branchial acid excretion. However, the recovery of blood pH was very rapid, and this eventually led to an over compensation due to a mixed respiratory and metabolic alkalosis. In the absence of any effect on branchial H ⁺ equivalent flux, the metabolic alkalosis induced by the β-agonist could be attributed to a stimulation of H⁺ equivalent exchange between extra- and intracellular compartments. We conclude that β-adrenergic responses play an important role in the regulation of postexercise blood acid-base status in seawater-adapted trout.

Comparison of absorption rates of halogenated phenols across fish gills in fresh and marine water

The absorption rates of five halogenated phenols across the gill epithelium of freshwater- and seawater-adapted rainbow trout was measured. At pH6, when the compounds mainly are present in the non-ionized form, the absorption rates in fresh water were higher than in seawater. At pH 9 no differences in absorption rates between the two water qualities were observed for those phenols present in ionized form. It is concluded that adaptation to seawater to some extent reduces the permeability of the gills for the nonionized forms of the compounds.

Acid-base regulation following acute acidosis in seawater-adapted rainbow trout, Salmo gairdneri: a possible role for catecholamines.

A fall in blood pH was induced by intra-arterial infusion of HCl in seawater-adapted rainbow trout (Salmo gairdneri). The acute acidosis resulting from HCl infusion caused a short-lived decrease in plasma bicarbonate concentration ([HCO3-]) and an increase in arterial CO2 tension (PaCO2). Erythrocyte pH and bicarbonate concentrations were not significantly altered by the infusion of acid. Injection of acid did, however, stimulate a branchial net H+ efflux which could be primarily accounted for by a net uptake of bicarbonate equivalent ions from the environmental water. Acid infusion of animals pre-treated with the beta-adrenergic blocking agent, propranolol, induced a similar pattern of change in plasma acid-base status. However, the recovery of plasma pH and restoration of plasma [HCO3-] were slower than in animals infused with acid alone. Red cell pH fell significantly in the face of plasma acidosis in the beta-blocked animals. Erythrocyte [HCO3-] showed a similar pattern of change to that of erythrocyte pH. Branchial net H+ efflux increased to a lesser extent following acid infusion in animals treated with propranolol. We conclude that catecholamines released into the bloodstream during periods of acute acidosis may play an important role in facilitating branchial H+ efflux in seawater-adapted rainbow trout.

Glomerular ultrastructure of the trout, Salmo gairdneri: effects of angiotensin II and adaptation to seawater.

The effect of angiotensin infusion on the glomerular ultrastructure of freshwater- and seawater-adapted rainbow trout. Salmo gairdneri, has been examined by scanning and transmission electron microscopy. Adaptation of trout to seawater resulted in epithelial podocyte flattening, primary process broadening and apparent loss of foot processes in almost all glomeruli, features which were uncommon in freshwater-adapted trout. Similar changes were induced by infusion of freshwater-adapted animals with angiotensin, suggesting that the renin-angiotensin system plays a role in the modification of glomerular epithelial ultrastructure. Adaptation of trout to seawater also reduced glomerular diameter, but infusion of freshwater-adapted animals with angiotensin did not mirror this effect. Infusion of angiotensin into seawater-adapted animals increased the overall thickness of glomerular basement membrane by increasing the lamina rara interna and lamina densa. This did not occur when freshwater-adapted fish were either infused with angiotensin or adapted to seawater. These findings suggest that other humoral systems are involved in the control of glomerular diameter and basement membrane thickness as part of an integrated response to increased environmental salinity.

Calcitonin induces hypercalcemia in grey mullet and immature freshwater and sea-water adapted rainbow trout

1. 1. Changes in plasma calcium levels, in response to salmon calcitonin injections, were studied in freshwater and sea-water adapted trout ( Salmo gairdnerii) and in grey mullet ( Chelon labrosus). 2. 2. Low doses (0.1 ng sCT/100g body weight) elicited hypercalcemia in the two species studied. 3. 3. High doses (0.5 μg) provoked hypocalcemia only in freshwater and sea-water adapted trout. 4. 4. An hypercalcemic response appears as the primordial effects of CT injections, higher doses of CT leading to hypocalcemic effects.

Inhibition of gill ( [formula omitted] in rainbow trout ( Salmo gairdneri) by a purine disulfide analog of adenosine triphosphate

The effect of the adenosine triphosphate analog, 6,6′-dithiobis(inosinyl imidodiphosphate), (sIMP-PNP) 2, was tested on the ouabain-sensitive ( Na + + K +)-ATPase (ATP phosphohydrolase, EC 3.6.1.3) and the ouabain-insensitive Mg 2+-ATPase in microsomes prepared from gill tissue of sea water-adapted rainbow trout, Salmo gairdneri. The ( Na + + K + )-ATPase was completely inhibited by low concentrations of (sIMP-PNP) 2 (6 μM) but the Mg 2+-ATPase was unaffected by the inhibitor at concentrations as high as 28 μM, supporting the suggestion that the two activities represent separate enzymes. The specificity of inactivation could be demonstrated both at a physiological temperature (13°C) and at 37°C. The rates of inactivation were similar at both temperatures. Inactivation of the ( Na + + K + )-ATPase by (sIMP-PNP) 2 was reversed by dithiothreitol, suggesting that the inhibitor forms a mixed disulfide with sulfhydryl groups on the enzyme. The inability of substrate (either ATP or its analog, adenyl-5′-yl imidodiphosphate) to protect against inactivation suggest that (sIMP-PNP) 2 is reacting with sulfhydryl groups which are not associated with the active site.

HCO3−-Dependent ATPase activity in the gills of rainbow trout Salmo gairdneri

1.1. A HCO3− activated ATPase is present in both fresh water and sea water adapted rainbow trout gills. The apparent Km for HCO3− is 0·016 M.2.2. Both the ATPase and active Cl− uptake by intact gills are inhibited by SCN−, but by apparently independent mechanisms.3.3.Cl− is not required for activation of the ATPase; at [Cl−] greater than 0·010 M, enzyme activity is inhibited4.4. The intracellular location of the HCO3− ATPase is unclear, but preliminary evidence suggests it is both mitochondrial and microsomal.

Sodium Efflux and Potential Differences across the Irrigated Gill of Sea Water-Adapted Rainbow Trout (Salmo gairdneri)

Sodium extrusion (J(out) (Na)) was measured across the gills of rainbow trout, Salmo gairdneri, adapted to sea water (SW) using a gill-irrigation system of small volume. The potential difference (TEP) was also measured under similar conditions. J(out) (Na) was usually between 100-250 microeq (100 g)(-1) h(-1), about an order of magnitude faster than in fresh water (FW)-adapted trout, but slower than has been reported for any other marine teleost. The TEP was between 10-11 mV, body fluids positive to SW. When the external medium was changed from SW to FW J(out) (Na) was reduced to about 25 % of the initial value, and the TEP was reduced by 40-50 mV (i.e. body fluids negative by 30-40 mV). Addition of either Na(+) or K(+) in SW concentrations reversed the changes; J(out) (Na) increased and the gill repolarized. The electrical behavior and sodium efflux in irrigated trout gill is qualitatively the same as has been reported for unanaesthetized, free-swimming fish of other species. Thus, the irrigated gill provides an adequate model for studying the mechanism of sodium extrusion in marine teleosts.

On the Mechanism of Sodium Extrusion across the Irrigated Gill of Sea Water-Adapted Rainbow Trout (Salmo gairdneri)

Sodium efflux (J(out) (Na)) across the irrigated trout gill was rapid in sea water (SW), but only about 25 % as large in fresh water (FW). The difference correlated with a change in the potential difference across the gill (TEP). The latter was about +10 mV (blood positive) in SW, but -40 mV in FW. Both flux and electrical data indicated that gills in this fish are permeable to a variety of cations including Na(+), K(+), Mg(2+), choline, and Tris. They are less permeable to anions; P(Na):P(K):P(Cl) was estimated to be 1:10:0.3, and P(Cl) > P(gluconate). The TEP was shown to be a diffusion potential determined by these permeabilities and the extant ionic gradients in SW, FW as well as in other media. J(out) (Na) appeared to be diffusive in all of the experiments undertaken. Exchange diffusion need not be posited, and the question of whether there is an active component remains open.

Experimental and structural analysis of the function of saccus vasculosus in rainbow trout, Salmo gairdneri (Richardson).

Injection of a saccus vasculosus homogenate from sea water adapted rainbow trout into the third brain ventricle of fresh-water rainbow trout increased the survival time of the latter in sea water of high salinity. This indicated an active role of saccus vasculosus in osmoregulation.