Glomerular disease in cultured rainbow trout, Salmo gairdneri Richardson, suffering from presumptive chronic viral haemorrhagic septicaemia

Abstract. Severe glomerular changes in the kidney of rainbow trout suffering from presumptive chronic viral haemorrhagic septicaemia are described. The pathological changes, as revealed by light- and electron microscopy, resembled those of membranous glomerulonephritis in mammals. Large electron-dense subendothelial-mesangial deposits were present in most glomeruli. A lattice-like arrangement of macromolecules was observed. Monocytes and macrophages were observed in the capillary convolute. The possibility of post-infectious disease nephropathy with aggregation of immunocomplexes in the capillary wall in fishes is discussed.     

Strawberry disease in rainbow trout, Salmo gairdneri Richardson

Abstract. Strawberry disease is a subchronic, non–debilitating, and non–fatal inflammatory skin disease of rainbow trout that has been recognized for the past 25 years. Morbidity ranges up to 80% and the disease affects fishes from 15cm in length to brood stock size. Epizootiological data indicate that strawberry disease usually appears, first in the autumn and reaches peak incidence during the following winter and spring. Data also indicate that the disease is found only in certain trout farms in the western and Pacific north–western regions of the United States. Although the cause of strawberry disease is unknown, the normal clinical course of 8 weeks can be reduced by oral treatment with oxytetracycline. Clinical signs include appearance of bright red, raised, circumscribed, ulcerated and indurated lesions in the skin that usually range up to 3 cm or more in diameter. Microscopically, the disease is characterized as a subchronic, focal, non–suppurative dermatitis with ulceration and extensive infiltration of mononuclear inflammatory cells.     

Proliferative kidney disease in rainbow trout Salmo gairdneri Richardson

Abstract. Two entirely separate outbreaks of PKD are described in an attempt to properly define the condition and enable it to be differentiated from other diseases of a similar nature. Losses of up to 75% of fingerling rainbow trout were recorded in one outbreak, illustrating the potentially serious nature of the disease. Although the kidneys showed the most obvious pathological changes, other organs were also affected. The host response was granulomatous in type, the foci of each cellular reaction being 5-20 μm eosinophilic cells considered to be parasitic. The cytoplasm of these cells contained numerous electron dense bodies some with a tail, but each with an electron lucent bar always orientated at right angles to the plasmalemma whenever they were near it. The most obvious cytoplasmic inclusion of these 'parasites' were other cells numbering up to five or six, each with its own nucleus and nucleolus, but devoid of any of the small electron dense bodies. The significance of either of these inclusions is unknown.
A limited differential diagnosis is given, and the argument presented that the condition PKD is the result of infection by a parasite, possibly an amoeba, in combination with poor quality water.     

Immunoglobulin heterogeneity in the rainbow trout, Salmo gairdneri Richardson

Abstract. Hetereogeneity of rainbow trout immunoglobulins was demonstrated by using monoclonal antibody 1A6 and polyacrylamide-gradient gel electrophoresis. Immunoglobulins defined by elisa using monoclonal antibody 1A6 were about 30% of the total immunoglobulins, detected by elisa using polyclonal antibodies, in healthy rainbow trout. In trout obtained from farms with a previous history of infectious viral diseases, 1A6-immunoglobulins were only about 14% of the total. Several serum pools from infected trout could be totally depleted of 1A6-immunoglobulins (about 12% of total immunoglobulins) by affinity chromatography over Sepharose immobilized monoclonal antibody 1A6. Polyacrylamide-gradient gel electrophoresis under denaturing conditions of total immunoglobulins, 1A6 immunoglobulins and no-1A6 immunoglobulins purified by affinity chromatography, showed a majority heavy chain of 70 KDa and a minority heavy chain of about 60 KDa, two light chains of 24 and 26 KDa, and a 11–14 KDa polypeptide.     

Direct electron microscopical visualization of the presumptive virus of viral haemorrhagic septicaemia (VHS) in the rainbow trout Salmo gairdneri Richardson and additional histopathological and haematological observations

Abstract. Electron microscopical and histopathological investigations were carried out on the anterior kidney often 1-year-old farmed rainbow trout naturally infected with the external signs of viral haemorrhagic septicaemia (VHS). The histopathology of the liver and the haematology of peripheral blood were also examined. The presumptive virus of VHS was directly demonstrated for the first time in the anterior kidney.
All diseased fishes showed necrotic changes in the kidney and the liver. The melano-macrophage centres of the anterior kidney showed a partial destruction accompanied with a loss of melanin. A progressive destruction of the erythrocytes was observed. The liver exhibited moderate to extensive necrosis (karyorrhexis and karyolysis with lymphocytic invasion in the necrotic areas). Neither intranuclear nor intracytoplasmatic inclusions were observed. In the peripheral blood diverse stages of erythrocytic degeneration, amitoses of the erythrocytes and a five-fold increase in lymphocyte numbers were observed.     

Phagocytic cells in the epidermis of rainbow trout, Salmo gairdneri Richardson

Abstract. Electron microscopical observations of skin of rainbow trout revealed the presence of several types of phagocytic cells in the epidermis, most notably macrophages, some of which were seen crossing the basal lamina. Occasionally, filament-containing cells showed either melanin granules or phagosomes, suggesting these cells were also capable of phagocytosis. No cells with the characteristics of the Langerhans cells were observed, which does not necessarily preclude the possibility of macrophages being able to play an identical role as antigen-trapping cells.     

Behaviour of rainbow trout, Salmo gairdneri Richardson, in marine cages

Abstract. Underwater television was used to observe the distribution and swimming behaviour of groups of farmed rainbow trout, Salmo gairdneri Richardson, in marine net cages. Undisturbed rainbow trout (mean total length 240 mm) aggregated near the surface, remaining motionless in slack water and formed polarized shoals at higher current velocities. Larger fish (mean total length 317 mm) occupied deeper parts of the cage and were more active during periods of slack water. The results are compared with previous work on farmed Atlantic salmon, Salmo salar L., and discussed in relation to the biology of wild rainbow trout and recent work on exercise, growth and condition in salmonids.     

The pathology of chronic ammonia toxicity in rainbow trout, Salmo gairdneri Richardson

Abstract. Two groups of rainbow trout fingerlings were exposed for 90 days to 0.2 and 0.4 mg/1 of un-ionized ammonia, respectively. Several fish exposed to the higher concentration soon developed clinical signs suggestive of a neurological dysfunction but subsequently recovered. No lesion attributable to ammonia was seen in the gills of any of the fish. This raises questions about the precise role of ammonia in the production of gill diseases in intensively cultured trout.     

Infectious haematopoietic necrosis in rainbow trout Salmo gairdneri Richardson in a semi-closed system

Abstract. An outbreak of infectious haematopoietic necrosis causing high mortality in rainbow trout fry occurred in New York State. Despite the fact that the hatchery effluent was recycled, spread of viral infection or of clinical disease was not demonstrated.
Endocardial and glomerular endothelial necrosis and fibrinous peritonitis were among the histopathologic changes seen. Many of the signs and lesions were similar to those seen in infectious pancreatic necrosis.     

A lymphosarcoma of thymic origin in the rainbow trout, Salmo gairdneri Richardson

Abstract. A rainbow trout with a malignant lymphoma of probable thymic origin showed direct spread of the tumour to the gills, metastases to the liver and head kidney, and the presence of abnormal circulating lymphocytes. The cells of the tumour possessed plasma membrane immunoglobulin detectable by immuno–fluorescence. Examination of the tumour cells by transmission electron microscopy revealed no evidence of virus associated with the cells. Infectious viruses could not be detected in the tumour tissue, and the tumour was not transmissible by injection of live tumour cells into young rainbow trout. Attempts to establish the tumour in long–term culture were unsuccessful.     

The kidney of rainbow trout, Salmo gairdneri Richardson, in the acute phase of viral haemorrhagic septicaemia: in vivo experiments on the renal excretion of fluid, electrolytes and protein

Abstract. Kidney function was studied in unanaesthetized rainbow trout, Salmo gairdneri Richardson, with acute infection by VHS virus strain F-l causing viral haemorrhagic septicaemia. The experiments were performed in diseased and control fish with catheters chronically implanted in the dorsal aorta and the urinary bladder. Glomerular clearance of polyfructosan, tubular handling of fluid and electrolytes and urinary excretion of protein were studied. In diseased fish, plasma concentrations of inorganic solutes were reduced, but plasma osmolarity and systemic blood pressure remained unchanged. Glomerular filtration rate and urine flow, both linearly correlated, were reduced from 5.20±0.40 to 3.08±0.66 ml/h/kg and from 2.51±0.15 to 1.63±0.28 ml/h/kg, respectively (±SEM). The urine osmolarity was augmented due to increased Na and Mg concentrations in the urine. Net tubular secretion of Mg was observed in diseased fish whereas net reabsorption of Mg prevailed in the controls. Decreased renal protein excretion rate prevented a renal loss of protein and, therefore, diminished plasma protein concentrations in VHS-infected fish may be attributed to extrarenal pathophysiological mechanisms.