Nephrocalcinosis

Physical Signs:

• Enlarged Kidneys: Noticeably swollen kidneys upon internal examination 1.
• Calcium Deposits: Visible white calcium deposits in the kidneys, detectable upon dissection 1.
• Abdominal Swelling: Distended abdomen due to fluid accumulation and enlarged kidneys 1.
• Pale Gills: Indicative of anemia and reduced kidney function 1.

Behavioral Changes:

• Lethargy: Reduced activity and slower swimming movements 1.
• Loss of Appetite: Decreased feeding behavior and subsequent weight loss 1.
• Abnormal Swimming Patterns: Fish may exhibit erratic or sluggish swimming due to discomfort 1.

Early Stages: Subtle signs such as reduced feed intake and slight lethargy 1.

Advanced Stages: Pronounced physical symptoms, including enlarged kidneys, calcium deposits, and increased mortality if not managed 1.

Impact on Fish Health: Nephrocalcinosis severely compromises kidney function, leading to impaired waste excretion, stress, and reduced growth rates 13.

Non-infectious Condition: Nephrocalcinosis is not caused by a pathogen but by environmental and dietary factors 12.

Contributing Factors:

• High Carbon Dioxide Levels: Elevated CO2 in the water can lead to metabolic imbalances and calcium precipitation in the kidneys 3.
• Water Alkalinity: High alkalinity levels contribute to the formation of calcium deposits 3.
• Dietary Imbalances: Excessive calcium or phosphorus in the diet can exacerbate the condition 3.

Environmental Factors: Poor water quality, especially high CO2 levels and alkalinity, can increase susceptibility to nephrocalcinosis 3.

Dietary Factors: Imbalanced diets with high calcium or phosphorus content can lead to the development of the condition 3.

• Histopathology: Microscopic examination of kidney tissues to identify calcium deposits and assess the extent of damage 2.
• X-ray or Imaging: Imaging techniques to visualize calcium deposits in the kidneys 3.
• Water Quality Testing: Assessing water parameters such as CO2 levels, alkalinity, and calcium content 1.

Current Treatments:

• Water Quality Management: Reducing CO2 levels and alkalinity in the water through improved aeration and water treatment systems 3.
• Dietary Adjustments: Balancing dietary calcium and phosphorus levels to prevent excessive accumulation in the kidneys 3.

Supportive Care:

• Monitoring Health: Regular monitoring of fish health and kidney function to detect and manage early signs of nephrocalcinosis 2.

Biosecurity Protocols:

• Implementing strict water quality management practices to maintain optimal conditions and prevent nephrocalcinosis 23.
• Regular monitoring of water parameters and fish health to detect early signs of imbalances 2.

Farm Management Practices:

• Adjusting feeding regimes to ensure balanced nutrition and prevent dietary imbalances 3.
• Implementing fallowing periods and site rotations to maintain water quality and reduce stress on fish populations 2.

• Norway (2010 - 2020s): Nephrocalcinosis has been increasingly observed in Norwegian salmon farming, particularly in recirculating aquaculture systems (RAS). The issue has been linked to suboptimal water quality, especially elevated levels of carbon dioxide (CO2). Research conducted by the Norwegian Veterinary Institute identified a significant rise in cases of nephrocalcinosis, prompting the industry to implement stricter monitoring and management practices to control CO2 levels and improve water quality. 6.

Nephrocalcinosis Incidence in Norway:

• Nephrocalcinosis is increasingly observed in farmed Atlantic salmon in Norway, with a significant prevalence across various facilities 6.
• The Norwegian Veterinary Institute reported nephrocalcinosis as an increasing issue, raising mortality rates and potentially severely decreasing fish welfare 7.

Geographical Spread:

• Nephrocalcinosis has been detected in multiple regions within Norway, with varying prevalence and severity across different facilities 6.
• The disease is particularly challenging to monitor due to the lack of visible external symptoms in affected fish 8.

Economic Impact:

• The economic impact of nephrocalcinosis is significant, as it affects fish health and survival, leading to increased costs for treatment and management 7.
• The disease poses a serious welfare challenge, necessitating better monitoring and management practices 6.

Treatment & Management:

• Current control measures include improved water quality management and dietary adjustments to balance calcium and phosphorus levels 8.
• Recent advancements in diagnostic techniques, such as adapted x-ray imaging, have been developed to screen for nephrocalcinosis in live fish in the field 7.
• Collaboration between researchers and fish farmers is essential to improve understanding and management of the disease 2.