Freshwater Rainbow Trout Research Articles

AMMONIA EXCRETION IN FRESHWATER RAINBOW TROUT (ONCORHYNCHUS MYKISS) AND THE IMPORTANCE OF GILL BOUNDARY LAYER ACIDIFICATION: LACK OF EVIDENCE FOR Na+/NH4+ EXCHANGE

Net ammonia fluxes (JAmm) were measured in adult freshwater rainbow trout in vivo under a variety of conditions designed to inhibit unidirectional sodium uptake (JinNa; low external [NaCl], 10(-4) mol l-1 amiloride), alter transbranchial PNH3 and NH4+ gradients [24 h continuous (NH4)2SO4 infusion, or exposure to 1 mmol l-1 external total ammonia at pH 8] and prevent gill boundary layer acidification (5 mmol l-1 Hepes buffer). Inhibition of JinNa with amiloride or low external [NaCl] under normal conditions reduced JAmm by about 20 %, but did not prevent the net excretion of ammonia during exposure to high concentrations of external ammonia. Increasing the buffer capacity of the ventilatory water with Hepes buffer (pH 8) reduced JAmm by 36 % and abolished the effect of amiloride on ammonia excretion. No evidence could be found to support a directly coupled apical Na+/NH4+ exchange. We suggest that any dependence of ammonia excretion on sodium uptake is caused by alteration of transbranchial PNH3 gradients within the gill microenvironment secondary to changes in net H+ excretion. Under normal conditions (pH 8, low external ammonia) gill boundary layer acidification facilitates over one-third of the total ammonia excretion. During exposure to high concentrations of external ammonia in poorly buffered water, estimates of transbranchial PNH3 gradients from measurements of bulk water pH and total ammonia concentration (TAmm) may be grossly in error because of boundary layer acidification. Prevention of boundary layer acidification with Hepes buffer during exposure to high cocncentrations of external ammonia revealed that the local transbranchial PNH3 gradient at the gill may in fact be positive (blood to water), negating the need for an active NH4+ transport mechanism. In freshwater trout, NH3 diffusion may account for all ammonia excretion under all experimental conditions used in the present study.

Morphological responses of the rainbow trout (Oncorhynchus mykiss) gill to hyperoxia, base (NaHCO3) and acid (HCl) infusions

Marked morphological responses occur in the gills of freshwater rainbow trout in response to experimental acid-base disturbance and these responses play an important role in acid-base correction. Compensated respiratory acidosis induced by 70h exposure to environmental hyperoxia (elevated water PO2) caused a 33% decrease in branchial chloride cell fractional surface area (CCFA). Metabolic alkalosis induced by normoxic recovery (6h) from hyperoxia (72h) caused a 50% increase in CCFA, whereas metabolic alkalosis induced by infusion (19h) of NaHCO3 caused a 70% rise. However, the largest increase (135%) in CCFA was seen in response to infusion (19h) of HCl. NaCl infusion had no effect. A particular goal was to assess the relative importance of changes in CCFA vs. changes in internal substrate (HCO3 (-)) availability in regulating the activity of the branchial Cl(-)/HCO3 (-) exchange system. For each of the experimental treatments, the accompanying blood acid-base status and branchial transport kinetics (Km, Jmax) for Cl(-) uptake had been determined in earlier studies. In the present study, a positive linear relationship was established between CCFA and J(Cl-) max in individual control fish in the absence of an acid-base disturbance. By reference to this relationship, observed changes in J(Cl-) max during metabolic acid-base disturbances were clearly due to changes in both CCFA and internal substrate levels (plasma [HCO3 (-)]) with the two factors having approximately equal influence.

Effects of zinc on the kinetics of branchial calcium uptake in freshwater rainbow trout during adaptation to waterborne zinc.

The effects of sublethal waterborne Zn2+ (150 micrograms l-1 = 2.3 mumol-1) on the kinetics of unidirectional Ca2+ influx were studied in juvenile freshwater rainbow trout during chronic exposure (60 days) at a water [Ca2+] of 1.0 mmol l-1. An unexposed group held under identical conditions served as control. The presence of Zn2+ in the water increased the apparent Km for Ca2+ influx by up to 300% with only a small inhibitory effect (35% at most) on the maximum rate of uptake (Jmax). These results, in combination with earlier data showing that Ca2+ competitively inhibits Zn2+ uptake, suggest that Zn2+ and Ca2+ compete for the same uptake sites. Acute withdrawal of Zn2+ after 3h of exposure resulted in a 23-fold reduction in Km for Ca2+, but a persistent small depression of Jmax. During prolonged exposure to Zn2+, the apparent Km for Ca2+ remained greatly elevated and Jmax remained slightly depressed. The actual Ca2+ influx in hard water ([Ca2+] = 1.0 mmol l-1) decreased marginally and paralleled the small changes in Jmax. The increases in apparent Km had a negligible influence on the actual Ca2+ influx because Km values (38-230 mumol l-1), even when elevated by Zn2+, remained below the water [Ca2+] (1000 mumol l-1). Rainbow trout exposed to Zn2+ exhibited a slower rate of protein synthesis in the gills (measured on day 23) and an increased tolerance to Zn2+ challenge (measured on both days 27 and 50). Unidirectional Zn2+ influx, measured at the end of the exposure period, was significantly reduced in the Zn2+-exposed fish. There were no changes in hepatic or branchial Zn2+, Cu2+ or metallothionein concentrations. We hypothesize that, during exposure to sublethal [Zn2+] in hard water, the fish may change the Km for a mutual Ca2+/Zn2+ carrier so as to reduce markedly Zn2+ influx without greatly altering Ca2+ influx. This reduced Zn2+ influx, rather than metallothionein induction, may be the basis of adaptation to elevated concentrations of waterborne Zn2+.

Inhibition of hepatic microsomal monooxygenase system by organotins in vitro in freshwater fish

The interaction in vitro of organotins tributyltin (TBT) and triphenyltin (TPT) with the hepatic microsomal monooxygenase systems in the freshwater fish, rainbow trout ( Oncorhynchus mykiss), European eel ( Anguilla anguilla), and bullhead ( Cottus gobio) was studied. Hepatic microsomes were incubated in vitro with TBT and TPT and various components analyzed. Ethoxyresorufin O-deethylase (EROD) activity was strongly inhibited by TBT and TPT in a concentration-dependent manner in all fish. Rainbow trout microsomes were more sensitive than were eel or bullhead microsomes. Total inhibition of EROD activity occurred both at 0.5 mM TBT and TPT in rainbow trout, whereas I mM decreased EROD activity to 15% (TBT) or 3% (TPT) in eel, and 35% (TBT) or 18% (TPT) in bullhead, respectively. As this effect may be caused by inhibition of different components of the microsomal electron transport system, different enzymes were studied separately. In all fish, both organotins led to a time- and concentration-dependent decrease in spectral total microsomal P450 content, and formation of cytochrome P420. TPT led to a greater inactivation of P450 enzyme than TBT, and induced a 50% loss in all fish at 0.08 mM TPT, whereas in case of TBT a 50% loss occurred at 0.18 mM in rainbow trout, 0.30 mM in bullhead, and 0.83 mM in eel. Cytochrome b 5 content was not affected, but both organotins led to an almost selective inhibition of either NADH or NADPH cytochrome c reductase activity in trout and eel, or of both in bullhead. Whereas TBT inhibited NADH cytochrome c reductase, TPT acted strongly on NADPH cytochrome e reductase. The study demonstrates species-related significant and selective effects of TBT and TPT on different components of the microsomal monooxygenase system in freshwater fish. This leads to inactivation of native enzymes and inhibition of enzyme activities.

Triiodothyronine is necessary for the action of growth hormone in acclimation to seawater of brown (Salmo trutta) and rainbow trout (Oncorhynchus mykiss)

Brown (BT) and rainbow trout (RT) in freshwater (FW) were treated with ovine growth hormone (GH), GH + iopanoic acid (IOP), and GH + IOP plus triiodothyronine (T3) for RT only. After 1 week of treatment, trout were transferred to 30 o/oo SW and treatment continued. In FW, GH treatment increased significantly plasma T3 level (BT) and T3/T4 ratio (BT and RT) by stimulating T4 to T3 deiodination. In the GH + IOP group, the plasma T3 levels and T3/T4 ratio fell significantly as T4 to T3 deiodination was inhibited. In GH + IOP + T3-treated RT, plasma T3 and T3/T4 ratios increased significantly relative to other groups. No mortality occurred and plasma osmolarity (PO) was not altered by any treatment in FW. After transfer to SW, all IOP + GH trout died within 2 (BT) or 3 days (RT). All GH-treated or control BT survived to the end of the experiment (6 days). RT survival rates tended to be improved in GH and GH + IOP + T3 groups relative to controls. Correlatively on day 1 the PO increase was significantly higher in IOP + GH groups (BT and RT) than in the other groups and significantly lower in GH and GH + IOP + T3 treated RT than in controls from days 1 to 6. These data confirm the requirement of T3 and deiodination of T4 to T3 for the development of hypoosmoregulatory mechanisms in SW as previously shown (Lebel and Leloup 1992). Furthermore, the suppression of the hypoosmoregulatory effect of GH, when conversion of T4 to T3 was inhibited by IOP and the reversal when T3 was added to IOP + GH treatment suggests that GH osmoregulatory action in SW acts via the simulation of T4-5' monodeiodination which increases T3 production.

Digestibility of various feedstuffs by post-juvenile chinook salmon ( Oncorhynchus tshawytscha) in sea water. 1. Validation of technique

This study was undertaken to assess whether the Guelph system for measuring digestibility in rainbow trout in fresh water was suitable for determining digestibility in chinook salmon held in sea water. Feces were collected from chinook salmon by the Guelph system, the stripping technique (once per week) and intestinal dissection. Validation of the Guelph procedure also involved assessment of: (1) the digestibility coefficients based on total fecal collection versus those based on the indirect chromic oxide indicator method, (2) the extent of nutrient leaching when using the Guelph system, and (3) the effect of level of dietary intake and extent of fish handling (due to stripping of feces) on estimates of nutrient digestibility by the Guelph method. No significant differences were found between the complete collection and indicator methods for measuring apparent nutrient digestibilities. Apparent digestibility values calculated using feces collected directly from the fish by both stripping and dissection were consistently lower than the complete collection and indicator values derived using the Guelph system. The stripping technique yielded the lowest digestibility coefficients. Nutrient leaching occurred when the feces had been exposed to sea water for more than 6 h. This was attributed to incomplete entry of feces into the collection column. Fish handling and concomintant reduction of food intake depressed digestibility coefficients for nutrients and energy and increased fish mortality. It is concluded that the Guelph system of fecal collection involving the use of Cr 2O 3 as the indigestible marker is a potentially reliable digestibility procedure for chinook salmon in sea water. However, care must be exercised to ensure rapid and complete removal of feces to the collection column to minimize nutrient leaching.

Proton Transport and Chloride Cells in the Gill of Rainbow Trout (Oncorhynchus mykiss)

Particulate preparations from freshwater rainbow trout (Oncorhynchus mykiss) gill homogenates contain an active magnesium ion activated ATPase that transports protons into the vesicles. Oligomycin at a concentration of 20 μg∙mL−1had little effect on the proton transport, which was completely inhibited by N-ethylmaleimide. This inhibition was partly counteracted by dithiothreitol. Proton transport in freshwater trout gill submitochondrial particles was completely inhibited by oligomycin. When freshwater trout were kept for 40 min in water equilibrated with air containing 5% carbon dioxide, their gill lamellar epithelium contained many cells densely covered with erect microvilli. After changing to water bubbled with room air, the cells rapidly lost their microvilli. Control fish that were killed immediately after removal from the storage tank also had microvilli, but less erect and fewer in number. Labelled latex microspheres and dextran were used as markers for external medium uptake into gill epithelial cells. The fish were pretreated by bubbling the water by air containing 5% carbon dioxide, and the uptake took place when the water was bubbled with room air.

Ammonia and urea excretion in Lahontan cutthroat trout (Oncorhynchus clarki henshawi) adapted to the highly alkaline Pyramid Lake (pH 9.4)

ABSTRACT Earlier studies have reported that acute exposure to alkaline pH strongly inhibits ammonia excretion in freshwater rainbow trout, but the Lahontan cutthroat trout thrives in Pyramid Lake, Nevada, at pH9.4. We investigated the rates and mechanisms of ammonia and urea excretion in this species in Pyramid Lake water to determine whether special strategies are employed to excrete nitrogenous wastes in an environment unfavourable for ammonia excretion. The majority of nitrogen wastes (N-wastes) were excreted as ammonia (56% through the gills, 10% through the kidney), while urea excretion accounted for 34% (32% gills, 2% kidney). Ammonia excretion was dependent on the NH3 partial pressure gradient across the gills and independent of Na+ influx and acidification of the gill water boundary layer. Acute exposure to more alkaline water (pH10) decreased ammonia excretion by 52%, while exposure to neutral water (pH7.6) increased ammonia excretion by 200%. When fish were held in a ‘closed system’ for 8h, ammonia excretion decreased as water ammonia levels increased over the first 6h. However, after 6h a marked increase in ammonia excretion occurred which may have been associated with an increase in the gradient and/or activation of a carrier-mediated transporter. We conclude that Lahontan cutthroat trout, adapted to pH9.4 water, maintain N-waste excretion by modifying mechanisms common to other teleosts. These modifications include lower rates of ammonia excretion, a higher ratio of urea excretion to ammonia excretion, a higher rate of renal ammonia excretion, greater plasma pH and greater total ammonia level (increased plasma ), which facilitate the diffusive excretion of NH3 across the gills, and a lack of dependence of ammonia excretion on Na+ influx.

The physiological responses of freshwater rainbow trout, Oncorhynchus mykiss, during acutely lethal copper exposure

Acutely lethal (24 h) exposure of adult rainbow trout (Oncorhynchus mykiss) to 4.9 μmol copper·l-1 in fresh water (pH 7.9, [Ca2+]≈0.8 mEq·l-1) caused a rapid decline of plasma Na+ and Cl- and arterial O2 tension, and initially a pronounced tachycardia. The internal hypoxia probably resulted from histopathologies observed in the gills of fish exposed to copper, such as cell swelling, thickening and curling of the lamellae, and haematomas. Copper cannot therefore be considered purely as an ionoregulatory toxicant during acutely lethal conditions. Mortality during exposure to copper could not simply be explained by the plasma ionic dilution, nor by the internal hypoxia, since arterial O2 content remained relatively unchanged. Secondary to the ionoregulatory and respiratory disturbances were a number of deleterious physiological responses which included a massive haemoconcentration (haematocrit values as high as 60%) and a doubling of the mean arterial blood pressure. The time-course of these changes suggest that cardiac failure was the final cause of death. In this respect copper exposure resembles low pH exposure in freshwater trout (Milligan and Wood 1982). Copper and H+ appear to be similar in both the primary site of their toxic action (the gills) and the secondary physiological consequences which result from acutely lethal exposures. Furthermore, the acute toxicity syndrome observed may be common to many metals which cause ionoregulatory and/or respiratory problems in freshwater fish.

Kidney and urinary bladder responses of freshwater rainbow trout to isosmotic NaCL and NaHCO3 infusion

ABSTRACT The relative roles of the kidney and urinary bladder in ion, fluid and acid-base regulation were examined in freshwater rainbow trout chronically infused with either 140 mmol I-1 NaCl or 140 mmol I-1 NaHCO3 (3mlkg-1h-1) for 32 h. NaCl had a negligible effect on blood ionic and acid-base status, whereas NaHCCh induced a metabolic alkalosis characterized by a rise in arterial pH and [HCO3-] and an equimolar fall in [Cl-]. Urine was collected via either an internal catheter, which bypassed bladder function, or an external urinary catheter, which collected naturally voided urine. As a percentage of the infusion rate, glomerular filtration rate increased by about 135%, but urine flow rate (UFR) by only 80 %, reflecting increased tubular reabsorption of H2O. During NaCl infusion, virtually all of the extra Na+ and Cl- filtered was reabsorbed by the kidney tubules, resulting in an increased UFR with largely unchanged composition. During Na HCO3- infusion, tubular Na+ and Cl- reabsorption again kept pace with filtration. HCO3- reabsorption also increased, but did not keep pace with filtration; an increased flow of HCO3--rich urine resulted, which excreted about 10% of the infused base load. At rest, fish fitted with external catheters voided in discrete bursts of about 0.85 ml kg-1 at 25 min intervals. During infusion, burst frequency increased by about 40 % and burst volume by about 20 %. Reabsorption by the bladder reduced UFR by 25 %, the excretion of Na+ and Cl - by 50 %, of K+ by 44 % and of urea by 25 %. These differences persisted on a relative basis during NaCl and NaHO3 infusion despite the decreased residence time. However, HCO3- was neither secreted nor reabsorbed by the bladder. We conclude that the freshwater kidney functions to remove as much NaCl as possible from the urine, regardless of the NaCl load, and this role is supplemented by bladder function. The bladder plays no role in acid-base regulation during metabolic alkalosis.

Tissue levels of oxolinic acid after oral or intravascular administration to freshwater and seawater rainbow trout

The concentrations of oxolinic acid in tissues of seawater-acclimated rainbow trout were compared with those of freshwater rainbow trout after a single oral administration (40 mg/kg). Up to 24 h after administration, little difference in the tissue concentrations was observed between the two groups of trout. However, tissue concentrations of the drugs in seawater trout decreased to undetectable levels by 72 h, whereas the concentrations in the freshwater trout peaked at 48 h and were detectable for at least 244 h. The kinetics of oxolinic acid uptake and excretion in the seawater trout was similar to that reported for seawater teleosts. Both groups of trout metabolized oxolinic acid by the same pathway, because the same oxolinic acid metabolites were observed in the bile of both groups of trout after a single oral administration. When oxolinic acid was injected (20 mg/kg) into the caudal vessels of each group of trout, serum levels of oxolinic acid decreased immediately after injection in both groups. Serum concentrations were 8.69 ± 2.14 μg/ml in the freshwater trout and 8.03 ± 2.27 μg/ml in seawater trout by 3 h after injection, respectively. Subsequently, the serum levels of oxolinic acid in the seawater trout decreased to barely detectable levels by 72 h. In contrast, oxolinic acid levels in freshwater trout were higher and persisted for longer, up to 244 h. These results confirm that oxolinic acid is excreted more rapidly in seawater trout than in freshwater trout.

Pharmacokinetic study of oxytetracycline in fish. I. Absorption, distribution and accumulation in rainbow trout in freshwater

The absorption, distribution and elimination of oxytetracycline in plasma, muscle, liver, intestine, mucus, skin and vertebrae in rainbow trout in freshwater were studied after a single dose of 150 mg/kg fish. The absorption of the drug was slow and only about 2.6% of the administered dose was absorbed at the time of maximum absorption. The distribution to all tissues of the fish was good, and a considerable affinity of OTC to tissues was observed. The slow elimination was demonstrated by the long halflife which was 11.6 days from plasma.

Renin, Atrial Natriuretic Peptide and Blood Plasma Ions in Parr and Smolts of Atlantic Salmon Salmo Salar L. and Rainbow Trout Oncorhynchus Mykiss (Walbaum) in Fresh Water and after Short-Term Exposure to Sea Water

ABSTRACT Freshwater Atlantic salmon (Salmo salar L.) smolts were abruptly transferred to sea water in May and over 3 days blood plasma ion concentrations were determined together with atrial natriuretic peptide (ANP) and plasma renin activity (PRA) using antibodies raised against human ANP and angiotensin I. Blood plasma Na+ and Cl− levels in smolts increased and, between 24 and 72 h, PRA increased significantly to 0.9ngml−1 h−1, while there was a gradual rise in ANP levels to 10pmoll−1 at 72 h. Similar measurements were made on parr transferred to sea water in September; in these fish Na+ and Cl− levels increased as in smolts, PRA remained unchanged at about 0.6ngml−1h−1 and ANP levels increased significantly to about 20pmoll−1 at 24 and 72 h. After 2h in sea water parr showed wide variability in ANP levels, in keeping with circulatory stress, hypoxia and increased atrial stretching. Parr transferred to sea water in December showed 10w drinking rates of 1.95 ml kg−1 h−1, even after 20 days, compared to a high drinking rate of about 7 ml kg−1 h−1 reported for smolts transferred in May. Rainbow trout acclimated to sea water for 3 weeks showed elevated levels of both ANP and PRA, similar to values reported for marine species. Freshwater rainbow trout fed a high-salt diet (12 % NaCl) showed significantly elevated levels of ANP compared to fish fed a normal diet (1.5 % NaCl), while PRA levels were depressed, though not significantly. It is concluded that, in fish acclimating to sea water, ANP is involved in excretion of salt 10ads, while the response to dehydration is activation of the renin-angiotensin system, which is required to initiate drinking. It is suggested that, in freshwater salmonids, as is the case in mammals, ANP and the renin-angiotensin system are antagonistic, but successful acclimation to sea water requires the systems, in alternation with the renin-angiotensin system, to ‘break through’ ANP suppression.

The Function of the Urinary Bladder In Vivo in the Freshwater Rainbow Trout

ABSTRACT Two different approaches were employed to examine the possible urine storage and ionoregulatory functions of the urinary bladder in vivo in the freshwater trout. An indirect approach, using non-catheterized fish, involved ‘spot sampling’ from the bladder to determine urine composition and measurement of PEG-4000 release into surrounding water to quantify urination events. The direct approach employed a new external catheterization technique to collect naturally discharged urine. Both methods demonstrated that trout urinate in intermittent bursts at 20–30 min intervals, and that natural urine flow rate is at least 20% lower and urinary Na+ and Cl− excretion rates at least 40 % lower than those determined by the traditional internal bladder catheter technique. The urine is stored for approximately 25 min prior to discharge, and significant ionic reabsorption via the bladder epithelium occurs during this period; a small residual volume is always likely to be retained. We conclude that previous studies using internal bladder catheterization have underestimated the ionoregulatory effectiveness of the entire renal system by preventing the function of the urinary bladder.

Effects of cortisol on gill chloride cell morphology and ionic uptake in the freshwater trout,Salmo gairdneri

Daily intramuscular injection of cortisol (4 mg kg−1 body weight) in rainbow trout,Salmo gairdneri, for 10 days caused significant increases in the number and individual apical surface area of gill chloride cells per mm2 of filament epithelium. Concomitantly, whole body influxes of sodium (Na+) and chloride (Cl−) increased. Acute (3 h) intra-arterial infusion of cortisol did not affect whole body Na+ or Cl− influx. A significant correlation was observed between both Na+ and Cl− influxes and the fractional apical surface area of filament chloride cells in control, sham (saline-injected) and experimental (cortisol-injected) fish. The chloride cells displayed similar ultrastructural modifications in trout undergoing cortisol treatment as in trout transferred to ion-deficient water. These findings suggest the existence of structure/function relationships in which branchial chloride cell morphology is an important determinant of Na+ and Cl− transport capacity. We conclude that chronic cortisol treatment enhances whole body Na+ and Cl− influxes by promoting proliferation of branchial chloride cells. The results of correlation analysis indicate that the chloride cell is an important site of NaCl uptake in freshwater rainbow trout.

Na+ and Cl− Uptake Kinetics, Diffusive Effluxes and Acidic Equivalent Fluxes Across the Gills Of Rainbow Trout: I. Responses To Environmental Hyperoxia

ABSTRACT Endogenous respiratory acidosis and metabolic alkalosis were induced in bladder-catheterized freshwater rainbow trout by exposure to environmental hyperoxia (72 h) and its subsequent removal. Unidirectional and net fluxes of Na+, Cl− and acidic equivalents across the gills were examined over 0.5 h intervals. Hyperoxia resulted in a positive Na+ balance, negative Cl− balance and net acidic equivalent excretion. Return to normoxia caused a negative Na+ balance, a positive Cl− balance and net basic equivalent excretion (=acidic equivalent uptake). Cl−/basic equivalent exchange was more important than Na+/acidic equivalent exchange in the homeostatic responses, and alkalosis was a more potent stimulus than acidosis for change in branchial ion fluxes. Kinetic analysis demonstrated that alterations in ion fluxes were achieved by complex changes in both the Km (inverse of affinity) and the Jmax (maximal transport rate) of the branchial C1−/HCO3− (OH−) and Na+/H+(NH4+) transporters. (control=165μequivl−1) and 114μequivl−1) were increased during hyperoxic acidosis to 250 and 44μ μequivl−1, respectively. (291μequiv kg−1h−1) and (456 μequiv kg−1 h−1) did not change significantly. During post-hyperoxic alkalosis, was further increased to 559μequivl−1, increased to 445μequivkg−1h−1, while and decreased to 137μequivl−1 and 309μequiv kg−1 h−1, respectively. Diffusive efflux was examined using a novel method. There was no significant differential diffusive efflux of Na+ and Cl− during hyperoxia but diffusive Na+ efflux exceeded Cl− efflux during posthyperoxic alkalosis, thereby serving as an additional mechanism for basic equivalent excretion.

Rainbow trout corpuscles of Stannius: stanniocalcin synthesis in vitro

In fresh-water rainbow trout, Oncorhynchus mykiss (formerly called Salmo gairdneri), experimentally induced mild hypercalcemia results in release of immunoreactive stanniocalcin from the corpuscles of Stannius (CS) and stimulated synthetic and releasing activities of the glands as measured in vitro. Pulse-chase experiments showed that stanniocalcin (STC) is a 56-kDa glycoprotein, processed from a 64-kDa precursor, prostanniocalcin (PSTC). PSTC and STC are homodimeric molecules that are readily split into monomers in the presence of reducing agents such as 2-mercaptoethanol. The monomeric form of PSTC and STC contains an approximately 5- to 6-kDa glycomoiety. Neither this sugar residue nor the NH2-terminal amino acid sequences of PSTC or STC proved to contain antigenic sites for the antiserum used in this study. Two-dimensional gel electrophoresis indicated the presence of several isoforms of PSTC and STC molecules that may reflect different stages of maturation of the (pro)hormone.

Scaling of atp-supplying enzymes, myofibrillar proteins and buffering capacity in fish muscle: Relationship to locomotory habit

ABSTRACT Pelagic fishes with an ability to swim in strong bursts have previously been shown to have large size-dependent increases (positive allometric scaling exponents) in the activities of glycolytic enzymes in white skeletal muscle. This scaling of glycolytic activity has been hypothesized to provide the anaerobic power supporting the size-independence of relative burst swimming speeds (body lengths s−1) in these fishes. This paper presents tests of several predictions of this hypothesis, using different-sized individuals of two pelagic teleosts, the kelp bass (Paralabrax clathratus) and the freshwater rainbow trout (Salmo gairdneri), and a flatfish, the Dover sole (Microstomus pacificus). In the two pelagic species, an increase in body size was accompanied by an increase in activities in white muscle (i.u. g wet mass of muscle−1) of lactate dehydrogenase (LDH), an indicator of potential for anaerobic glycolysis, and creatine phosphokinase (CPK), an enzyme that helps maintain stable ATP concentration during muscular activity. Activities of citrate synthase (CS), an indicator of the potential for aerobic metabolism, decreased with size. In the flatfish, activities of all enzymes in white muscle decreased with body size, a trend proposed to reflect lack of adaptive value of strong burst swimming ability in this benthic fish. Activities of LDH and CS were size-independent in brain of flatfish, indicating that the scaling patterns observed in the muscle of this species were related to muscle function, not to common, organism-wide changes with size. In white muscle of P. clathratus, total protein and soluble protein concentrations and buffering capacity increased with body size in parallel, but myofibrillar protein was size-independent. These results suggest that the capacity for anaerobically powered work and the maximal potential to generate force scale only modestly in relation to total body mass and therefore do not appear to be functionally related to the pattern of glycolytic scaling. Thus, these data support the hypothesis that the functional role of the strongly positive scaling of glycolytic enzymes in the white muscle of pelagic fish is to provide increased power during burst swimming in larger-sized fishes.

Induction of metallothionein gene expression by cadmium and the retention of the toxic metal in the tissues of rainbow trout ( Salmo gairdneri)

1. When rainbow trout were exposed to cadmium by intraperitoneal injection, there was a rapid (within 3hr) and significant (approx. 63%) loss of the metal from the whole bodies of the fish. 2. Of the metal retained in the bodies of the fish (approx. 37% of the injected dose), more than 98% was accounted for collectively among the liver, kidney and gills. 3. Subsequent maintenance of the rainbow trout in fresh water for up to 98 days post-metal administration, indicated that there was no further loss of the cadmium accumulated in the organs studied and that the distribution of the metal among the liver, kidney and gills remained unchanged over that period. 4. During this 98-day period of maintenance of the fish, tissue concentrations of metallothionein-specific mRNA and metallothionein protein were quantified using riboprobe and ELISA systems respectively. Metallothionein-specific mRNA concentrations increased rapidly (within 24 hr) before falling back to levels similar to, or slightly greater than, those found in control animals. The concentration of metallothionein protein also increased significantly (within 3 days) then remained elevated thereafter. 5. Throughout the experimental period, the concentrations of zinc and copper were also monitored in the liver, kidney and gills of the rainbow trout. The concentrations of each ion differed between each of the organs but did not change during the experiment. 6. The induction of metallothionein gene expression by cadmium in the liver, kidney and gill of rainbow trout and the subsequent sequestration of the toxic metal is discussed with regard to the relative levels of these other essential metal ions.

Effect of repetitive cortisol and thyroxine injections on chloride cell number and Na +/K +-ATPase activity in gills of freshwater acclimated rainbow trout, Salmo gairdneri

1. 1. Freshwater nonanadromous rainbow trout, Salmo gairdneri, were injected three times a week with either saline, 10μg cortisol/g, 1.0μg thyroxine/g or 10μg cortisol/g + 1.0μg thyroxine/g during a period of 28 days (12 injections). A separate group was derived as a subgroup from the thyroxine group on day 14 and received Cortisol + thyroxine from day 14 until day 28 (six injections). 2. 2. Gill chloride cell number and Na +/K +-ATPase activity increased by cortisol treatment, the changes being significant on days 7 and 14, respectively. 3. 3. Thyroxine treatment did not affect gill Na +/K +-ATPase activity or chloride cell number directly. Neither did it modify the stimulatory effect of cortisol on these parameters. 4. 4. Muscle water decreased in cortisol-treated fish and increased in thyroxine-treated fish, while no changes were observed in the combined hormone groups. 5. 5. No changes were observed in plasma chloride in any group during the experiment. 6. 6. The results demonstrate a putative role of cortisol in stimulating hypo-osmoregulatory mechanisms and suggest that thyroxine is without a direct or a supportive effect for cortisol action.