Nephracalcinosis in Rainbow Trout (Oncorhynchus mykiss) I: Macroscopic pathology, slight cases

The nephracalcinosis is a kidney pathology that is characterized by salt deposits of calcium and magnesium in the kidney and other tissues. It is associated to degeneration and a chronic inflammatory response.

You cannot see external clinical signs in the sub-clinical presentation of the disease. Many times you can only see renal histopathological lesions or focused deposits at the kidney level. As the disease progresses the external clinical signs are characterized by a swollen belly, exophthalmos and death. Internally the affected fish show a pale liver, ascites, renal paleness and variable calcification in the kidney.

Introduction

If the fish is exposed to high leves of CO2, it reduces de pH in the blood and at the same time decreases the affinity of the hemoglobin to transport oxygen. A chronic exposure to high levels of CO2 produce mineral deposits in all the organs, mainly, the kidney, mostly made up of calcium phosphate.

This is a common condition for the salmonids that are being farmed in an open flow system and a closed system. The rainbow trout (O. mykiss) is the most susceptible species to this condition. It is true that this condition has been endemic in salmonids that have been exposed to high levels of CO2, but during the 2008-2009 season it has been seen more often and its severity has been increasing. This could be related to the increase in farming the rainbow trout (O. mykiss) in hatcheries.

Smart (1979) reported that the rainbow trout (O. mykiss) that are exposed to concentrations of CO2 of 12, 24 and 55 mg/lit for 270 and 385 days produce between a 4.8%, 9.7% and 45.2% of nephrocalcinosis.

Macroscopic clinical signs

The clincal signs depend on the level of CO2 and how long the fish were exposed to it. In many sub-clinical cases you could only see a decrease in the growth, increase in the conversion rate if the fish have been constantly submitted to stress. In clincal cases the fish are lethargic, swim on the surface of the water, and externally you can see a bilateral exophthalmos, a swollen belly and in certain situations you can see an anal protrusion.

Internally the fish have ascites, a pale liver, renal paleness, renomegaly and in a variety of calcium deposits in the renal tubules, and interstitial tissue. Occasionally, you can see spleenomegaly.

The main consequences of this condition are that the fish have a predisposition to infections such as Flavobacteriosis or Infectious Pancreatic Necrosis. The damage to the kidney could cause a failure in the osmoregulatory after it has been transferred to the sea, to a high level of laggers and the fish that have a variety of deposit forms in their stomachs show feeding disorders.

Clinical classification of the disease

Depending on the percentage of the damaged kidney, the nethrocalcinosis can be classified into 4 categories:

Table 1: Classifying the clincal nephrocalcinosis according to the severity of the findings.

 

Condition of the disease

 

Morphological findings

 

Slight

Isolated calcareous deposits, affecting less than 50% of the length of the ureters. The population shows decrease in growth and increase in the conversion factor.

 

Moderate

Over 50% of the length of the ureters shows calcareous deposits. You can see that they are dilated. In some conditions you can see that the later part of the kidney is affected and renomegaly affecting less than 30%. The population shows a decrease in their growth and an increase in the conversion factor.

 

Severe

Over 50% of the ureters show marked calcareous deposits. The ureters are dilated and snake like. Externally the fish show abdominal dilation. Internally, you can see ascites, pale liver, pale kidney, renomegaly. The population shows a decrease in the growth and increase in the conversion factor.

 

It is possible to diagnose the clincal disease by the presence of calcareous deposits in the kidney in a variety of shapes.

The diagnosis for the sub-clincal conditios is through the use of histology and by measuring the blood parameters such as the creatinine, which is an indicator of the kidney's functionality.

Table 2. Dignosing the Neghrocalcinosis in the farmed salmonids

+ Presence of findings, - Absence of findings; ** Values over what is considered normal

 

Condition of the disease

Morphological findings

Histopathological findings

Clinic Pathology

(Creatinine) **

Sub-clinical

-

+

+

Clinical

+

+

+

Figure 1: Rainbow trout (Oncorhynchus mykiss), affected by a slight nephrocalcinosis condition. You can see calcification in less than 50% of the ureters.

Figure 2: Rainbow trout (Oncorhynchus mykiss), affected by a slight nephrocalcinosis condition. You can see isolated calcareous deposits.

Figure 3:  Rainbow trout (Oncorhynchus mykiss), affected by a slight nephrocalcinosis condition. You can see calcification in less than 50% of the ureters.

Figure 4: Rainbow trout (Oncorhynchus mykiss), affected by a slight nephrocalcinosis condition. You can see calcification in less than 50% of the ureters.

La nefrocalcinosis es patología renal, que se caracteriza por  el depósito de sales de calcio y magnesio en el riñón y otros tejidos, asociado a degeneración y  una respuesta inflamatoria crónica.

La presentación subclínica de la enfermedad no se observan signos clínicos externos, y en muchas ocasiones se observan solo lesiones histopatológicos renales o la presencia de depósitos focales a nivel renal. Cuando la enfermedad progresa, los signos clínicos externos se caracterizan por distención abdominal, exoftalmía y muerte. Internamente los peces afectados presentan hígado pálido, ascitis, palidez renal y calcificación variable del riñón.

Introducción

La exposición a altos niveles de CO2 produce inicialmente una reducción del pH de la sangre, lo cual a su vez disminuye la afinidad de la hemoglobina de transportar oxígeno. La exposición crónica a altos niveles de CO2 produce depósitos de minerales en todos los órganos, principalmente riñón, compuestos principalmente por fosfato de calcio.

Es una condición comun en salmónidos cultivados en sistemas de flujo abierto y cerrado siendo la trucha arcoiris (O. mykiss), la especie más suceptible a esta condición. Si bien la condición ha sido endémica en salmónidos expuestos a altos niveles de CO2, durante la temporada 2008-2009 su frecuencia y severidad se ha incrementado, probablemente relacionado a un incremento del cultivo de truchas (O. mykiss) en pisciculturas.

Smart (1979), reporta que trucha arcoiris (O. mykiss), expuestas a concetraciones de CO2 de 12, 24 y 55 mg/l por 270 y 385 días,  producen entre un 4,8 % , 9,7 % y 45,2 % de nefrocalcinosis.

Signos clínicos macroscópicos

La presentación de signos clínicos depende del nivel de CO2 y tiempo de exposición. En casos subclínicos, en muchos  solo se observa dismición del crecimiento, incremento de la converción, estando los peces somentidos crónicamente a estrés. En casos clínicos los peces afectados presentan letargia, natación superficial, externamente se observa exoftalmía bilateral,  distensión abdominal y en ciertos casos se describe protrusión anal. En los casos severos se presenta mortalidad asociadas.

Internamente los peces presentan ascitis, hígado pálido, palidez renal, renomegalia y de forma variable depósitos de calcio en los túbulos renales, uréteres y tejido interticial. Ocasionalmente se observa esplenomegalia.

Entre los principales consecuencias de esta condición se encuentran la predisposición a infecciones tales como Flavobacteriosis o Necrosis Pancreática Infecciosa. El daño renal puede asociarce a un falla en la capacidad osmoregulatoria, post ingreso al mar, a un alto porcentaje de peces rezagados y aquellos peces que presentan de forma variable depósitos a nivel del estómago, presentan disfunsión alimentaria.

Clasificación clínica de la enfermedad

De acuerdo al porcentaje del riñón afectado la nefrocalcinosis puede ser clasificada en 4 categorias.

Tabla 1: Clasificación de nefrocalcinosis clínica de acuerdo a la severidad de los hallazgos.

osotomayor_00215
La enfermedad clínica es posible diagnosticarla mediante la presencia de depósitos calcáreos en el riñón de forma variable.

La condición sunclínica se diagnostica mediante el uso de histología o mediante la medión de parámetros sanguíneos como la creatinina, indicador de funcionamiento renal.

Tabla 2: Diagnóstico de Nefrocalcinosis en el cualtivo de salmónidos.

+ Presencia de hallazgos; - Ausencia de hallazgos; ** Valores por sobre lo considerado normales.osotomayor_00216

Figura 1: Trucha arcoiris (Oncorhynchus mykiss), afectado por un cuadro de nefrocalcinosis leve. Se observa calcificación de menos del 50 % de los uréteres.

Figura 2: Trucha arcoiris (Oncorhynchus mykiss), afectado por un cuadro de nefrocalcinosis leve. Se observa depósitos calcáreos aislados.

Figura 3: Trucha arcoiris (Oncorhynchus mykiss), afectado por un cuadro de nefrocalcinosis leve. Se observa calcificación de menos del 50 % de los uréteres.

Figura 4: Trucha arcoiris (Oncorhynchus mykiss), afectado por un cuadro de nefrocalcinosis leve. Se observa calcificación de menos del 50 % de los uréteres.

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