Field Case Study: Hidden Challenges in Atlantic Salmon Smolts – Nephrocalcinosis and Hemorrhagic Smolt Syndrome

During a recent post-sales technical assistance visit to a flow-through hatchery, we encountered a case that perfectly illustrates the complexity of fish physiology and the critical importance of comprehensive monitoring.

At first glance, the fish (Atlantic Salmon, avg. 170g) appeared robust, displaying an excellent condition factor (K=1.32) and ATPase levels indicating an advanced state of smoltification. However, the presence of fungal infections and scale fragility prompted a deeper investigation.

Key Findings:

By utilizing portable diagnostic technology (i-STAT) combined with detailed necropsies, we identified a concomitant presentation of Nephrocalcinosis and Hemorrhagic Smolt Syndrome (HSS).

The clinical biochemistry profile revealed:

Acid-Base Imbalance: Distinct alkalemia (pH 7.42) and hypercapnia (elevated pCO2).

Metabolic Compensation: Hypochloremia and hyperbicarbonatemia, suggesting the fish were actively compensating for chronic respiratory acidosis—likely driven by high CO2 levels associated with stocking density (30 kg/m³).

Tissue Damage: Severe mineral deposits in the kidneys (amorphous carbonate apatite).

Why is this case relevant?

The most striking aspect of this study is the resilience of the salmon. Despite severe kidney pathology and HSS, the fish maintained efficient osmoregulation.

This case highlights how nephrocalcinosis acts as a silent but serious welfare issue, often triggered by the complex interaction between water quality, diet, and stocking density.

In the full article, we break down the pathophysiology step-by-step, present the complete clinical biochemistry tables, and discuss the implications for production and nutritional management.

For more details, please download the full article here:

-> Full Article English Version.

-> Artículo Completo Versión Español.