Parasitic Kidney Disease in Rainbow Trout: How One Breton Fish Farm Beat the Odds

KAMAHU — Tue, 07 Jul 2026 09:50:35 +0000

This case study demonstrates how alternativ agroecological principles transformed disease control at a commercial rainbow trout farm in Brittany, in the context of global warming.
The practices described were tracked using KAMAHU’s data-driven aquaculture management software which has been in place at the farm since 2016.

The original and official text can be found here : https://hal.inrae.fr/hal-05677497v1
Robert Le Coat, Christophe Jaeger. L’hépatonéphrite parasitaire (Tetracapsula bryosalmonae) : Témoignage d’un changement gagnant de pratiques en élevage de truite arc-en-ciel (Oncorhynchus mykiss). 9èmes Journées de la Recherche Filière Piscicole, Itavi, Jun 2026, Rennes, France. ⟨hal-05677497⟩

ABSTRACT

Proliferative Kidney disease (Tetracapsula bryosalmonae) is a disease that occurs when the water temperature exceeds 15°C and can cause losses of over 90%. There is no cure or preventive treatment, and the advice is to limit the effects of the disease in reducing food quantity delivered to a minimum.
Agroecology focuses on improving animal health by addressing the causes of the disease in order to adapt farming practices and reduce its effects. The case study presented illustrates such a change in rainbow trout (Oncorhynchus mykiss) farming practices. Fry are raised in recirculating water systems, fed with well water at a constant temperature of 12°C and free of the parasite. For fry from spring eggs, the strategy is to infect them while rearing them in water below 15°C, before transferring them, at the end of summer, to outdoor raceways supplied with water from river. For fry from autumn eggs, the individuals remain naive to the parasite until they are transferred to raceways in mid-summer. In this way, regardless of the batch, the young trout develops the disease under rearing conditions that do not allow it to progress to clinical cases. The trout thus acquire immunity that lasts until they reach commercial size. In this way, overall health standards have been improved up to a loss rate of around 5%, which in turn has improved growth rates.
This example sets out the strategies to be adopted to control this infection and adapt practices according to the configuration of each affected fish farm.

The Challenge: A Disease That Thrives in Warm Water

Proliferative Kidney Disease (PKD), caused by the parasite Tetracapsula bryosalmonae, represents one of the most significant threats to rainbow trout (Oncorhynchus mykiss) farming. The disease emerges when water temperatures exceed 15°C, and without intervention, it can cause mortality rates exceeding 90 percent.

Crucially, there are no curative or preventive treatments available. Traditional advice has been to minimize feed input during outbreaks, but this approach fails to address the root cause and results in significant production losses.

At Pisciculture du Dourduff in Plougoulm, Brittany—a farm producing approximately 200 tons of rainbow trout annually—PKD had been a persistent problem since at least the 1990s. After the 2003 ban on malachite green (previously used in combination with formalin), the farm needed a new strategy.

The Solution: Rethinking Farm Practices Through Agroecology

Rather than seeking technological or biochemical solutions, the farm embraced an agroecological approach: understanding the disease’s life cycle and adapting farming practices to disrupt it.

Understanding the Parasite’s Life Cycle

PKD has a complex lifecycle:

The parasite’s spores are released from its host—a freshwater bryozoan (Fredericella sultana)—when water temperatures rise above 9°C.
Free-swimming spores remain infectious for only 12–24 hours.
They enter fish through gills and skin.
Clinical disease manifests only when water exceeds 15°C in naïve (previously unexposed) fish.
Fish that survive initial exposure develop immunity specific to the local parasite strain.
The parasite cannot transmit directly from fish to fish; it must return to bryozoans to complete its cycle.

The Innovative Farming Strategy

The farm implemented two distinct rearing protocols based on spawning season:

1. Spring-Spawning Fry (Summer Alevins)

Raised in recirculating aquaculture systems (RAS) fed with parasite-free groundwater at a constant 12°C.
From July onward, controlled amounts of river water (containing the parasite) are gradually introduced.
Temperature is carefully managed to remain below 15°C through precise mixing of groundwater and river water.
Fish become infected but do not develop clinical disease due to the controlled temperature.
In September, after the critical high-temperature period, fish are transferred to outdoor raceways at ~15g.

2. Autumn-Spawning Fry (Winter Alevins)

Also raised in RAS with parasite-free groundwater.
Kept naïve to the parasite until mid-summer transfer to raceways.
First exposure occurs during the critical period (July-August) when fish weigh ~100g.
The late exposure means the infection develops after the peak temperature period.
More mature fish with stronger immune systems can fight the infection before it becomes clinical.

This approach ensures that all fish develop immunity under conditions that prevent the disease from reaching clinical stages, providing protection through to commercial size.

Building of the RAS in 2018

The Results: From 60% Losses to 95% Survival

The transformation in farming practices delivered dramatic improvements:

Batch	Initial Number	Mortalities	Survival Rate
1 (Old method)	80,000	36,667	54.2%
2 (Old method)	130,000	75,059	42.3%
3 (Old method)*	160,000	18,970	88.1%
4 (New method)	50,000	4,976	90.1%
5 (New method)	55,241	5,209	90.6%
6 (New method)	68,234	10,076	85.3%
7 (New method)	60,000	4,349	92.8%
8 (New method)	85,000	7,807	90.8%

*Batch 3 used groundwater at the start of grow-out, unlike other old-method batches

Key Improvements:

Survival rate from fry to market: Increased from ~42% to ~93%.
Growth performance: Autumn-spawned trout now reach 800g at 14 months (vs. 250g previously).
Production efficiency: Requires 55% fewer eggs to meet production targets (140,000 vs. 300,000 for spring batches).
Antibiotic use: Significantly reduced due to improved overall health.
Farmer well-being: Eliminates the stress of summer mortality events.

How Farm Software Enabled This Transformation

The success of this approach relied on precise data management—where specialized aquaculture software played a crucial role:

Temperature Monitoring & Control
- Daily water temperature tracking from river and groundwater sources.
- Historical data (available since 1992) enabled identification of the “critical period”.
- Near real-time water mixing to maintain optimal temperatures in RAS.
Production Tracking
- Monitoring fish growth rates across different batches and rearing systems.
- Tracking survival rates at each life stage.
- Managing the transition timing between RAS and raceways.
Water Quality Management
- Monitoring oxygen levels (with jet platform systems in all basins).
- Tracking water source usage (groundwater vs. river water ratios).
- Ensuring parasite-free water supply for vulnerable life stages.
inventory & Planning
- Managing egg arrivals (April and November deliveries).
- Planning production cycles to align with temperature patterns.
- Reducing egg purchases through improved survival rates.

Key Success Factors

The farm’s success depended on several critical elements:

Access to parasite-free groundwater – Essential for maintaining naïve fish and controlling exposure timing
Recirculating aquaculture systems – Enabled precise temperature control and efficient use of limited groundwater
Additional infrastructure – A new RAS building constructed in 2018 near a second groundwater source
Daily monitoring – Consistent temperature tracking was indispensable for timing transfers and water mixing

Conclusion: A Model for Climate-Resilient Aquaculture

This case study demonstrates that even without medical treatments, significant disease control is possible through adaptive farming practices. As climate change increases water temperatures, PKD and similar diseases will become more prevalent. The approach developed at Pisciculture du Dourduff provides a practical, cost-effective model that other farms can adapt to their specific configurations.

The key insight: By understanding the pathogen’s biology and leveraging available resources (groundwater, RAS technology), farms can turn a major production constraint into a manageable challenge. The use of farm management software to track temperatures, growth rates, and water quality parameters was instrumental in implementing and refining this approach.

While further research is needed to fully understand the immunization mechanisms, this case proves that agroecological principles combined with precise data management can deliver sustainable solutions in aquaculture.

The KAMAHU team visiting the Moulin du Dourduff trout farm in 2020 with its actual manager Amaury GUET (on the right)

Farming – Fish Farm Management Software