Variations in renal corpuscular morphology with adaptation to sea water in the rainbow trout, Salmo gairdneri Richardson

The kidneys of similar sized rainbow trout from freshwater and seawater environments were examined and several parameters of renal corpuscular morphology were measured, The glomeruli of the seawater trout were significantly smaller and contained significantly fewer red blood cells than those of the freshwater fish. There was also some evidence of a decreased number of renal corpuscles per unit area, and an increased proportion with no apparent capsular space in the seawater trout.     

Sulphamerazine toxicity in cut-throat trout broodfish Salmo clarki (Richardson)

Treatment of cut-throat trout broodfish Salmo clarki (Richardson) with Sulphamerazine at 220 mg/kg (10 g/100 1b) of fish/day for 14 days resulted in severe kidney histopathology and increased mortality among males. Experimental data presented showed that cut-throat trout broodfish were extremely sensitive to Sulphamerazine toxicity. Hydropic degeneration of renal tubule epithelium and haemorrhage into tubule lumens were observed in kidneys of both male and female trout, but was more severe in the former. Death, which occurred only in males, was correlated with spawning stress and impaired renal function.     

Effect of excess vitamin D3 on calcium metabolism in rainbow trout Salmo gairdneri Richardson

The effect of excess vitamin D₃ on calcium metabolism in rainbow trout was investigated. Trout were reared for 24 weeks on diets containing 4000, 104 000 or 1 004 000 iu of supplemental vitamin D₃ kg^-1 dry diet. No effect of excess vitamin D₃ was detected in the weight gain, feed efficiency or total mortalities of trout in the different groups. None of the fish showed any signs of hypercalcaemia and no significant difference was detected in the calcium, magnesium, phosphorus and sodium content of the trout vertebrae or total carcass. However, there was a significant increase in the calcium, magnesium and phosphorus content of the skin in trout reared on the highest supplemental level of vitamin D₃ (1 004 000 iu kg^-1 diet). No overt signs of renal calcinosis were detected in any of the trout. This study indicates that trout are resistant to excess vitamin D₃, and that excess vitamin D₃ does not appear to be related to the increased incidence of renal calcinosis in rainbow trout.     

Ontogeny of IgM-producing cells in the lymphoid organs of rainbow trout, Salmo gairdneri Richardson: an immuno- and enzyme-histochemical study

The ontogenetic development of IgM-containing cells is described as demonstrated by immunoperoxidase staining with a mouse anti-trout IgM monoclonal antibody and the differentiation of enzyme-histochemical markers in the non-lymphoid cells forming the stroma of the thymus, spleen and kidney of the rainbow trout. The first lymphoid cells staining with the monoclonal antibody occurred at day 4-5 after hatching in the renal lympho-haemopoietic tissue. By 1 month after hatching IgM-positive cells also appeared in the spleen and thymus. Enzyme-histochemical demonstration of the alkaline and acid phosphatase and non-specific σ-naphthyl acetate esterase enzymatic activities in the non-lymphoid cells indicated that a certain degree of maturation of the cellular stroma of the developing lymphoid organs of trout was reached before or at the time when IgM-expressing cells could be observed. The relationships of the stromal components of the various lymphoid organs to the development of IgM-positive cells, and the possible role of the renal lympho-haemopoietic tissue as a primary lymphoid organ for B-cell differentiation in the trout are discussed.     

Cloning of rainbow trout SLC26A1: involvement in renal sulfate secretion

The kidney plays an important role in ion regulation in both freshwater and seawater fish. However, ion transport mechanisms in the teleost kidney are poorly understood, especially at the molecular level. We have cloned a kidney-specific SLC26 sulfate/anion exchanger from rainbow trout (Oncorhynchus mykiss) that is homologous to the mammalian SLC26A1 (Sat-1). Excretion of excess plasma sulfate concentration after Na2SO4 injection corresponded to significantly higher expression of the cloned SLC26A1 mRNA. Detailed morphological observation of rainbow trout renal tubules was also performed by light microscopy and transmission electron microscopy. According to the structure of brush border and tubular system in the cytoplasm, renal tubules of rainbow trout were classified into proximal tubule first and second (PI and PII) segments and distal tubules. In situ hybridization revealed that SLC26A1 anion exchanger mRNA is specifically localized in the PI segment of kidneys from both seawater- and freshwater-adapted rainbow trout. With immunocytochemistry, Na+-K+-ATPase and vacuolar-type H+-ATPase were colocalized to the same cells and distributed in the basolateral and the apical membranes, respectively, of the cells where the SLC26A1 mRNA expressed. These findings suggest that the cloned kidney-specific SLC26A1 is located in kidney proximal tubules and is involved in excretion of excess plasma sulfate in rainbow trout.     

Transmission of Tetracapsuloides bryosalmonae (Myxozoa: Malacosporea) to Fredericella sultana (Bryozoa: Phylactolaemata) by various fish species

Tetracapsuloides bryosalmonae is a myxozoan parasite of salmonids and freshwater bryozoans, which causes proliferative kidney disease (PKD) in the fish host. To test which fish species are able to transmit T. bryosalmonae to bryozoans, an infection experiment was conducted with 5 PKD-sensitive fish species from different genera. Rainbow trout Oncorhynchus mykiss, brown trout Salmo trutta, brook trout Salvelinus fontinalis, grayling Thymallus thymallus and northern pike Esox lucius were cohabitated with T. bryosalmonae-infected Fredericella sultana colonies and then subsequently cohabitated with statoblast-reared parasite free Bryozoa. Statoblasts from infected colonies were tested by PCR to detect cryptic stages of T. bryosalmonae, which may indicate vertical transmission of the parasite. In this study, brown trout and brook trout were able to infect Bryozoa, while there was no evidence that rainbow trout and grayling were able to do so. Few interstitial kidney stages of the parasite were detected by immunohistochemistry in brown trout and brook trout, while rainbow trout and grayling showed marked proliferation of renal interstitial tissue and macrophages with numerous parasite cells. Intraluminal stages in the kidney tubules were only detected in brown trout and rainbow trout. In contrast to previous observations, pike was not susceptible to PKD in these trials according to the results of T. bryosalmonae-specific PCR. No DNA of T. bryosalmonae was detected in any statoblast.     

Transport physiology of the urinary bladder in teleosts: a suitable model for renal urea handling?

The transport physiology of the urinary bladder of both the freshwater rainbow trout (Oncorhychus mykiss) and the marine gulf toadfish (Opsanus beta) was characterized with respect to urea, and the suitability of the urinary bladder as a model for renal urea handling was investigated. Through the use of the in vitro urinary bladder sac preparation urea handling was characterized under control conditions and in the presence of pharmacological agents traditionally used to characterize urea transport such as urea analogues (thiourea, acetamide), urea transport blockers (phloretin, amiloride), and hormonal stimulation (arginine vasotocin; AVT). Na(+)-dependence and temperature sensitivity were also investigated. Under control conditions, the in vitro trout bladder behaved as in vivo, demonstrating significant net reabsorption of Na(+), Cl(-), water, glucose, and urea. Bladder urea reabsorption was not affected by pharmacological agents and, in contrast to renal urea reabsorption, was not correlated to Na(+). However, the trout bladder showed a threefold greater urea permeability compared to artificial lipid bilayers, a prolonged phase transition with a lowered E(a) between 5 degrees C and 14 degrees C, and differential handling of urea and analogues, all suggesting the presence of a urea transport mechanism. The in vitro toadfish bladder did not behave as in vivo, showing significant net reabsorption of Na(+) but not of Cl(-), urea, or water. As in the trout bladder, pharmacological agents were ineffective. The toadfish bladder showed no differential transport of urea and analogues, consistent with a low permeability storage organ and intermittent urination. Our results, therefore, suggest the possibility of a urea transport mechanism in the urinary bladder of the rainbow trout but not the gulf toadfish. While the bladders may not be suitable models for renal urea handling, the habit of intermittent urination by ureotelic tetrapods and toadfish seems to have selected for a low permeability storage function in the urinary bladder.     

Kidney pathology and parasite intensity in rainbow trout Oncorhynchus mykiss surviving proliferative kidney disease: time course and influence of temperature

Proliferative kidney disease (PKD) is an endoparasitic disease of salmonids caused by the myxozoan parasite Tetracapsuloides bryosalmonae. We recently described the development of the disease from initial infection until manifestation of clinical disease signs in rainbow trout held at 2 water temperatures, 12 and 18°C. The aim of the present study is to investigate whether (1) infected fish surviving the clinical phase would recover from renal pathological changes, (2) whether they would be able to reduce the parasite load in the kidneys, and (3) whether water temperatures would influence renal recovery and parasite clearance. At 18°C, fish showed a gradual recovery of normal kidney morphology which was associated with a decline in parasite numbers and infection prevalence. Fish kept at 12°C initially showed an enhancement of kidney lesions before recovery of normal kidney morphology took place. The decrease in renal parasite load was retarded compared to 18°C. The results from the present study provide evidence that rainbow trout surviving the clinical phase of PKD are able to (1) fully restore renal structure, and (2) significantly reduce renal parasite loads, although 100% clearance was not achieved within the experimental period of this study. Water temperature influences the rate but not the outcome of the recovery process.     

Evidence for an intrarenal renin-angiotensin system in the rainbow trout, Oncorhynchus mykiss

Physiological and molecular approaches were used to investigate the existence of an intrarenal renin-angiotensin system (RAS) in rainbow trout. Inhibition of angiotensin-converting enzyme by captopril (5 x 10(-4 )M) rapidly decreased vascular resistance of the trunk of the trout, perfused at 19 mmHg, resulting in an increased perfusate flow rate and a decreased intrarenal dorsal aortic pressure. A profound diuresis occurred in the in situ perfused kidney and reflected both increased glomerular filtration rates and decreased water reabsorption (osmolyte reabsorption was unchanged). Renal and vascular parameters recovered once captopril treatment was stopped. Diuretic and vascular effects of captopril on the in situ trout kidney concur with an inhibition of known vasoconstrictor and antidiuretic actions of angiotensin II. However, at a higher perfusion pressure (28 mmHg), captopril had no effect on intrarenal aortic pressure or perfusate and urine flow rates, suggesting that the trout intrarenal RAS is activated by low perfusion pressures/flows. Existence of the renal RAS in trout was further supported by evidence for angiotensinogen gene expression in kidney as well as liver.     

Immunohistochemical localization of rainbow trout ladderlectin and intelectin in healthy and infected rainbow trout (Oncorhynchus mykiss)

In the present study, the pattern of immuno-reactive ladderlectin and intelectin in healthy rainbow trout is compared to rainbow trout infected with a variety of infectious agents. In healthy rainbow trout, both proteins were localized to individual epithelial cells of the gill and intestine and both proteins were clearly demonstrated within cytoplasmic granules of polymorphonuclear leucocytes and macrophages/monocytes found in blood vessels, hepatic sinusoids, renal interstitium, mucosal epithelium and submucosa of normal intestine. In tissue from infected rainbow trout, there was an overall relative increase in both lectins compared to healthy fish and both proteins were detected in extra-cellular spaces surrounding bacteria, fungi and protozoa. Increased distribution and density of both RTLL and RTInt was demonstrated along mucosal surfaces and within inflammatory leucocytes in infected tissues and immune related organs. These findings represent one of the few examples of in vivo association of defence lectins and infectious agents.     

Renal regulation of acid-base balance in a freshwater fish (1).

Intra-arterial injection of a fixed acid load caused only a short-lived (less than 2h) disturbance of blood pH but a long lived (2-3 days) elevation of urinary acid excretion in freshwater trout (Salmo gairdneri). The renal response comprised an immediate increase in acid output in the form of titratable acidity minus bicarbonate, and a slower rise in acid output in the form of ammonia. The total elevation in urinary acid efflux over 72h was such that no other mechanism besides renal function is needed to explain the ultimate compensation of this experimental acid-base disturbance.     

Kidney function in response to salt feeding in rainbow trout (Salmo gairdneri Richardson)

1. The effect of high levels of dietary salt up to 12% NaCl on kidney function in freshwater rainbow trout was investigated. 2. Renal response to dietary NaCl load includes increases in urinary flow rate and glomerular filtration rate, together with a slight reduction in ionic reabsorption capacity. 3. The renal salt excretion rate, which was doubled to about 100 microM/kg/hr, in fish fed the high salt diet, is not entirely a consequence of a reduction in tubular ionic reabsorption but also of increased glomerular filtration. 4. The role of the endocrine system in control of renal salt excretion is discussed.     

A fish model of renal regeneration and development

The fish kidney provides a unique model for investigating renal injury, repair, and development. Like mammalian kidneys, fish kidneys have the remarkable ability to repair injured nephrons, designated renal regeneration. This response is marked by a recovery from acute renal failure by replacing the injured cells with new epithelial cells, restoring tubule integrity. In addition, fish have the ability to respond to renal injury by de novo nephron neogenesis. This response occurs in multiple fish species including goldfish, zebrafish, catfish, trout, tilapia, and the aglomerular toadfish. New nephrons develop in the weeks after the initial injury. This nephrogenic response can be induced in adult fish, providing a more abundant source of developing renal tissue compared with fetal mammalian kidneys. Investigating the roles played by different parts of the nephron during development and repair can be facilitated using fish models with differing renal anatomy, such as aglomerular fish. The fish nephron neogenesis model may also help to identify novel genes involved in nephrogenesis, information that could eventually be used to develop alternative renal replacement therapies.     

Chronic, sublethal nickel acclimation alters the diffusive properties of renal brush border membrane vesicles (BBMVs) prepared from the freshwater rainbow trout

Brush border membrane vesicles (BBMVs) were prepared from the kidneys of rainbow trout exposed acutely (72 h; 13,380 microg Ni L(-1)), chronically (11 months; 289 microg Ni L(-1)), or chronically and acutely, to waterborne nickel (Ni). Uptake of 63Ni into renal BBMVs was temperature-dependent and fitted a two component kinetic model composed of a saturable, Michaelis-Menten component prominent at lower Ni concentrations, and a moderate linear diffusive component apparent at higher Ni concentrations. Chronic Ni exposure reduced the permeability of the BBM to Ni, evidenced by a significantly reduced slope of the linear diffusive component of BBMV uptake. Efflux of Ni from 63Ni-loaded renal BBMVs was not significantly altered by acute Ni challenge. Both Ca2+ and Mg2+ inhibited uptake of Ni into renal BBMVs when present at a molar ratio to Ni of 1000:1. Mg2+-induced inhibition, however, was concentration-dependent and significant in BBMVs prepared from chronically Ni-acclimated fish at far lower molar ratios of 100 and 10 to 1. The data suggest that subtle, long-term modulation of membrane structure and function in the rainbow trout may be a compensatory response to chronic waterborne Ni exposure. Additionally, the data challenge the assumptions of constancy of the physiological parameters underlying physiologically based approaches to modeling metal toxicity. Such approaches are currently employed to derive water quality criteria for some metals.     

The effects of hypophysectomy, prolactin therapy and environmental calcium on electrolyte balance of the brown trout Salmo trutta, L.

Adaptation of the brown trout to fresh water containing increasing concentrations of calcium resulted in a decrease in plasma electrolyte level and total electrolyte excretion. The electrolyte excretion rate was higher at the beginning than at the end of the urine collection periods. Hypophysectomized fish had a lower plasma electrolyte concentration than the controls. This deficiency was partially corrected by polactin therapy. High environmental calcium was only effective to a limited extent. There was no difference in the normal renal sodium output between hypophysectomized and intact fish in fresh water. Environmental calcium did not have any significant effect on renal electrolyte output of hypophysectomized fish.     

Branchial and renal (Na+/K+) ATPase and carbonic anhydrase activities in a eurythermal freshwater teleost, Carassius auratus L

1. Plasma sodium and chloride levels were determined in goldfish, Carassius auratus L., following acclimation to 5, 15, 25 and 35 degrees C. Carbonic anhydrase and (Na+/K+)-stimulated ATPase activities of gill and kidney were also assayed at both acclimation temperature and 41 degrees C. 2. Consistent with earlier findings this eurythermal species exhibits more variation in plasma composition with temperature than do the more stenothermal salmonids. Seasonal changes were also observed. 3. Despite differences in detail the overall pattern of transport enzyme activity change with acclimation was comparable to that previously observed in trout. The goldfish is, however, notable for high levels of renal carbonic anhydrase activity, and presumably employs this system more than does the trout to drive urinary recovery of ions by H+:Na+ and HCO3-:Cl- exchanges.     

Evidence that infectious stages of Tetracapsula bryosalmonae for rainbow trout Oncorhynchus mykiss are present throughout the year

Proliferative kidney disease (PKD) is a hyperplastic condition of the lymphoid tissue of salmonids infected with the spores of Tetracapsula bryosalmonae, a myxozoan parasite formerly designated PKX, which has recently been described as a parasite of several species of bryozoans. The occurrence of PKD is generally associated with seasonal increase in water temperature, with research indicating that transmission of the disease does not occur below 12 to 13 degrees C. This suggested that the infectious stages are absent from about November to March/April. Here we document the transmission of PKD at water temperatures and seasons previously considered to be non permissive for PKD infection. The exposure of naive rainbow trout Oncorhynchus mykiss (Walbaum) to PKD-infected water ranging from 8 to 13 degrees C during the Autumn, Winter and early Spring, resulted in the infection of kidney interstitium once the trout were transferred to 16 degrees C. In addition, cohabitation studies were conducted with the bryozoan host Fredericella sultana collected from a river at times of low seasonal temperatures because this bryozoan species overwinters as living colonies. Cohabitation of trout with colonies of F sultana in parasite-free city water at 16 degrees C, also led to renal lymphoid tissue infection with the parasite and even to nephromegaly. Our results provide evidence that the infectious stages of T bryosalmonae for rainbow trout were present in the water throughout the entire year and that the impact of temperature on the development of PKD is primarily a result of the kinetics of Tetracapsula multiplication in bryozoan and fish hosts.     

Renal function in the freshwater rainbow trout after dietary cadmium acclimation and waterborne cadmium challenge

Renal function was examined in adult rainbow trout (Oncorhynchus mykiss) after chronic exposure to a sublethal level of dietary Cd (500 mg/kg diet) for 52 d and during a subsequent challenge to waterborne Cd (10 microg/L) for 72 h. Dietary Cd had no major effects on UFR (urine flow rate) and GFR (glomerular filtration rate) but caused increased renal excretion of glucose, protein, and major ions (Mg(2+), Zn(2+), K(+), Na(+), Cl(-) but Ca(2+)). However, dietary Cd did not affect any plasma ions except Na(+) which was significantly elevated in the Cd-acclimated trout. Plasma glucose and ammonia levels fell by 25% and 36% respectively, but neither plasma nor urine urea was affected in Cd-acclimated fish. Dietary Cd exposure resulted in a remarkable increase of Cd load in the plasma (48-fold, approximately 22 ng/mL) and urine (60-fold, 8.9 ng/mL), but Cd excretion via the kidney was negligible on a mass-balance basis. Clearance ratio analysis indicates that all ions, Cd, and metabolites were reabsorbed strongly (58-100%) in both na?ve and dietary Cd exposed fish, except ammonia which was secreted in both groups. Mg(2+), Na(+), Cl(-) and K(+) reabsorption decreased significantly (3-15%) in the Cd-exposed fish relative to the control. Following waterborne Cd challenge, GFR and UFR were affected transiently, and only Mg(2+) and protein excretion remained elevated with no recovery with time in Cd-acclimated trout. Urinary Ca(2+) and Zn(2+) excretion rates dropped with an indication of renal compensation towards plasma declines of both ions. Cadmium challenge did not cause any notable effects on urinary excretion rates of metabolites. However, a significant decrease in Mg(2+) reabsorption but an increase in total ammonia secretion was observed in the Cd-acclimated fish. The study suggests that dietary Cd acclimation involves physiological costs in terms of renal dysfunction and elevated urinary losses.     

Differential handling of urea and its analogues suggests carrier-mediated urea excretion in freshwater rainbow trout

The possible presence of urea transport mechanisms in the gill and kidney of the freshwater rainbow trout (Oncorhynchus mykiss) was investigated in vivo by comparing the branchial and renal handling of analogues acetamide and thiourea with the handling of urea. Trout were fitted with indwelling dorsal aortic catheters and urinary catheters and injected with an isosmotic dose of [(14)C]-labeled urea analogue (acetamide or thiourea) calculated to bring plasma analogue concentrations close to plasma urea concentrations. Urea and analogue concentrations were significantly greater in the urine than in the plasma. Branchial clearance rate of acetamide was only 48% of urea clearance, whereas the clearance of thiourea was only 22%, a pattern that was also observed in branchial uptake of these substances and was similar to our previous observations in toadfish and midshipmen. The renal secretion clearance rates of urea and acetamide were similar, and on average, both substances were secreted on a net basis, although reabsorption did occur in some cases. In contrast, thiourea was neither reabsorbed nor secreted by the kidney tubule. The secretion clearance rates of both acetamide and urea were well correlated with the secretion clearance rates of Na(+), Cl(-), and water, whereas there was no relationship between thiourea and these substances. The pattern of acetamide, thiourea, and urea handling by the gill of the trout is similar to that found in the gills of the midshipman and the gulf toadfish and strongly suggests the presence of a UT-type facilitated diffusion urea transport mechanism. The pattern of differential handling in the kidney is unlike that in the gill and also unlike that in the kidney of the midshipman and the gulf toadfish, suggesting a different mechanism. In addition, renal urea secretion occurs against a concentration gradient, suggesting the involvement of an active transport mechanism.