Managing the Dissolved Oxygen Balance of Open Atlantic Salmon Sea Cages: A Narrative Review

As Atlantic salmon depend on dissolved oxygen (DO) to survive and grow, managing DO is essential for welfare and growth. However, the dynamics of DO in the open sea cages are complex, caused by a range of factors that interact and create compounding effects. To understand DO dynamics, two pillars of knowledge are essential: the supply of DO to the cages and the consumption of DO in the cages. The components of these two pillars vary greatly across both time and space, with factors including ambient sea temperature and current, density stratification, fish size, health and metabolism, biomass density and distribution, topography, production routines and farm configuration. In the production environment, these factors often interact, making related analyses on effects, causality and effective management highly challenging. Exacerbating matters, existing knowledge is fragmented across multiple disciplines, making it challenging for end-users to access. Using sensors is often necessary to understand and manage the complexity of DO, and the interest to implement digital technologies to aquaculture operations and utilize big data analyses is growing, but to succeed in the application, an in-depth understanding of the relevant dynamics is necessary. Consequently, this review is produced to compile existing knowledge on the many factors that influence the consumption or supply of DO in the sea cages, and their relationship to each other. In this narrative review, we explore the known interactions and compounding effects between these factors, and synthesize it in a causal diagram for holistic analyses of the DO balance.