Establishing the code of best practices for Atlantic salmon gill health in a multifactorial world

The GillHealthAct project acknowledges that in a multifactorial world, achieving production targets may carry biological penalties.

Gill health of Atlantic salmon is influenced by numerous intermingling factors that require a holistic understanding of causation and correlation. We address this call by focusing on how the gills respond (short-term) and adapt (long-term) to several biological and environmental factors, which are considered determining and predisposing factors for gill health.

The empirical data together with historical insights, are expected to form the basis of an evidence-based framework for best practices that support and promote optimal gill health of farmed Atlantic salmon. 

Background

Gill diseases represent a significant challenge in the global marine and freshwater finfish aquaculture. In Norway, gill diseases are identified as the major cause of reduced growth, inferior welfare and increased mortality in farms.

In particular, gill health-related challenges have increased in the last years and are considered the most pressing health issue in salmon, particularly during sea cage production. These challenges have become a severe financial burden for the industry.

It is often, however, that gill challenges are presented simultaneously, and no prominent primary causal agent could be established – thus, termed complex gill disease. In fact, the Fish Health Report 2022 documented that the increase in the number of cases of gill problems in recent years is predominantly complex or multifactorial in nature.

The technical meeting on Gill Health on the 16th of March 2023 in Værnes attended by different industry actors discussed the pressing issue of gill health challenges requiring immediate and active prevention and mitigation strategies. There were several key points highlighted, including

1. environment plays a significant role in the severity of gill health challenges, where sub-optimal conditions increase infection pressure and simultaneously present stress to the gills;
2. besides temperature and known pathogens, identification of other environmental variables contributing to gill diseases is necessary – where the potential influence of smolt production practices, especially water quality have been identified,
3. compromised gill health due to algae and jellyfish blooms is concerning; however, sporadic, intermittent occurrence and absence of diagnostic tools make mapping difficult.

Thus, there is a need for a consolidated effort to integrate current knowledge and develop tools and proactive measures addressing these gill health challenges in farmed salmon. 

Goal

The GillHealthAct will answer the following questions:

• What do historical data indicate on the environmental drivers of increased cases of sub-optimal gill health in farms?
• What farm measures must be revisited and finetuned based on integrating historical data, current trajectories, and experimental results?
• How does rearing history contribute to the increased susceptibility to gill health-related challenges in the farms?
• What provisions must define a good framework for developing code for best practices to ensure optimal gill health?

What we do

The expected project outputs are multifaceted and relevant nationally and internationally, especially in salmon-producing countries.

The benefits will go beyond salmon farming, as the strategy for best practice framework can be applied to other farmed species.

The results are beneficial to the different sectors of aquaculture, specifically in salmon farming, including researchers and academics, fish health service providers, farmers and technology suppliers, and national and international regulatory and legislative agencies.

The GillHealthAct will develop models and non-invasive tools to assess gill health. We will contribute to reducing the use of live animals by adapting and developing in vitro models for gill health-related studies. This will contribute to toolboxes that are being implemented to safeguard gill health.

The GillHealthAct will identify the contribution of RAS to the susceptibility of salmon to gill-related disorders. This Project will explore whether the RAS environment is a predisposing factor to the increased susceptibility to gill health challenges at sea. The expected data will be valuable in optimising land-based production and, at the same time, identifying protocols that may reduce the risk of gill diseases.

The GillHealthAct will document the consequences of climate-related stressors on salmon gill health. Documenting these effects will help site selection of new farms, e.g., avoiding areas where erratic temperatures and blooms are expected.

The biological data will also feed current climate models, thereby finetuning them and making them even more robust. This information and these models are important for aquaculture’s potential for developing climate adaptation strategies.

The GillHealthAct will adopt a continuous and active dialogue with industry stakeholders. Their inclusion in this dynamic process will allow us to provide them with a best practice framework suitable for the prevailing conditions and, simultaneously, dynamic and iterative. The close link that will be fostered will facilitate an effective and fast transfer of knowledge that can improve the conditions on the farms.

Ultimately, the GillHealthAct will develop a framework and best practices guidelines for salmon gill health. The code of best practice that will be drafted in this Project will provide the salmon aquaculture industry with a set of dynamic guidelines that identify the risks of production practices and establish mitigation measures.

Further, this will develop into proactive and reactive health management tools in the farms.