Welfare and resilience in aquaculture

Abstract

As the world population is continuing its growth, the resilience of the aquaculture industry is essential to ensure that it can sustainably meet the growing demand for seafood, while minimizing the negative impact of the environment and ensuring good welfare of the cultured organisms. In this special issue, we have compiled nine original articles that provide an overview of the different aspects between resilience and welfare, and how those two notions are closely connected and contribute to the sustainability and ethical functioning of aquaculture systems.

In the first article, Meijboom and Bovenkerk (2025) explored the concept of resilience in fish aquaculture, emphasizing that it involves not only the biological capacity of individual fish but also the overall aquaculture system. The authors encourage a holistic view that integrates both the robustness of fish and the adaptability of aquaculture systems while addressing moral concerns. The authors further discussed the ethical dimensions of resilience, including the assumptions of “win-win” scenarios, trade-offs between individual welfare and system efficiency, the need to center animal agency, and the potential moral implications of adapting fish to challenging conditions.

Challenging conditions in an aquaculture context include housing, as fish are usually kept at high densities in a relatively stimulus-free environment. These conditions can have a negative impact on the welfare and mental state of the animal. Epping et al. (2025) used the judgment bias paradigm (Mendl et al., 2009) to assess the impact of different standard laboratory housing conditions on the mental states of female guppies. The guppies showed no significant stress response to variations in standard housing conditions, indicating their adaptability. These results showed the resilience of guppies to standard housing conditions and confirmed the utility of the judgment bias paradigm as a tool for assessing fish welfare, which can be extrapolated to ensuring optimal living conditions in aquaculture settings.

Atlantic salmon (Salmo salar) is one of the key aquaculture species, being considered a “climate friendly” protein source due to its good growth, utilization of feed resources, low carbon footprint, and greenhouse gas emission (Aas et al., 2022; Singh et al., 2024). Nevertheless, the salmon industry is facing several challenges regarding resilience and welfare, including the sea lice crisis, which caused mass mortalities and economical losses (Powell et al., 2018). The article from Rosendal et al. (2025) presents a Norwegian case study exploring the factors explaining why policy instruments to stimulate breeding for lice resistance in salmon aquaculture are currently absent, despite documented opportunities for selection progress. This study highlights the potential of breeding for lice resistance to enhance aquaculture resilience by reducing reliance on harmful delousing treatments and improving fish welfare.

Cleaner fish, such as the lumpfish (Cyclopterus lumpus), have been identified as an alternative, or complementary biological solution to the rougher chemical, mechanical, and thermal treatments (Powell et al., 2018). The study from Ytteborg et al. (2025) showed that chemicals such as hydrogen peroxide and peracetic acid can cause significant skin damage to lumpfish when the two delousing treatments are applied concomitantly. These results emphasize the need for careful management of the husbandry protocols, not only for the species of interest but also for the cleaner fish, to maintain lumpfish welfare and resilience.

Feed, feed ingredients, and feeding protocols are also at the center of attention when talking about the resilience of the aquaculture sector, both from a welfare and an economical perspective. An important point for the successful establishment of a new aquaculture species is the potential for early acceptance to formulated feed. The article from Guo et al. (2025) determined the optimal diagnostic morphometric indicators to assess the nutritional status and causes of mortality in juvenile black rockfish (Sebastes schlegelii), a major inshore species for commercial and recreational purposes in China, Japan, and Korea, who recently became an important species for aquaculture and stock enhancement (Guo et al., 2020). The identification of the key morphometric parameters affected by starvation in these juveniles provides valuable insights for establishing appropriate feeding protocols to enhance the welfare of hatchery-reared black rockfish.

Similarly, it is primordial for successful establishment of a new species in aquaculture to optimize feeding protocols. The Atlantic wolffish, Anarhichas lupus, has been identified as a good candidate cold-water aquaculture diversification (Moksness, 1994). Wolffish species are known for their docile behavior, a high tolerance to stress, and has the ability to feed on formulated diet early on (Foss et al., 2004; Imsland et al., 2009). Knowing the lipid and protein requirements for the optimal growth and welfare of a novel species is the basis to develop a sustainable diet and ensure the resilience of the aquaculture sector. Hinchcliffe, Roques, Roos, et al. (2025) found the optimal dietary protein requirements for juvenile Atlantic wolffish, which should be between 50% and 60%. As proteins are a precious resource, 50% are recommended as a trade-off for a cost-effective feeding strategy, ensuring optimal growth and economical resilience.

Traditionally, aquaculture feed was highly dependent on protein and oils from fishmeal, which was not a sustainable strategy (Miles & Chapman, 2006). Land-based protein sources were then gradually replacing fishmeal in fish feed (Daniel, 2018). However, this solution also raises environmental and welfare questions when potential feed for human is used to feed carnivorous fish species (FAO, 2020). Alternative protein and oil sources from lower trophic species or side streams have the potential to contribute to the resilience of aquaculture sector by reducing the dependency on finite fishmeal and oil supplies. The study from Warwas et al. (2025) evaluated the potential of three fish processing side streams (sprat trimmings, marinated herring, and mackerel in tomato sauce) as fish feed ingredients for rainbow trout (Onchorhynchus mykiss). The sprat and mackerel side streams were identified as promising raw materials for fish feed, supporting a circular approach to increase marine protein and lipid production.

The resilience of the aquaculture sector might also involve to move away from the traditional open-cage culture system toward closed containment systems. Systems such as recirculating aquaculture systems (RAS) have a lower dependency on external water sources (Ahmed & Turchini, 2021). They also allow for a better control of the environmental conditions, such as temperature, and have the potential for a better health and welfare (Øvrebø et al., 2022; Van Rijn, 2013). As fish are ectotherms, meaning their body temperature is dependent on the environmental temperature, it is important to know the optimal temperature for each life stage of a species to ensure optimal growth and welfare. Hinchcliffe, Roques, Ekström, et al. (2025) showed that Atlantic wolffish reared at 15°C showed reduced growth, higher metabolic rates, and compromised gut barrier function compared to those at 10°C (control), indicating that warming increases energy expenditure while impairing growth. These findings highlight the challenges of rearing Atlantic wolffish at higher temperatures and offer insights for improving their welfare in aquaculture and understanding their responses to temperature changes in the wild.

The welfare of fish in RAS needs to be monitored efficiently, and farmers need to be able to react rapidly to avoid mass losses. As with other nonverbal farmed organisms, we need to rely on indirect parameters to assess the welfare status of fish in aquaculture. Haematological parameters, such as haemoglobin levels, are good indicators for the health and welfare status of an organism (Frisch & Anderson, 2005). The traditional Drabkin method is not suitable for field measurement, as it takes time and requires the use of toxic cyanide-based chemicals and laboratory equipment. Portable analysers, generally designed for human blood, are good potential alternatives, but they first need to be calibrated and validated for fish blood (Clark et al., 2008). A new portable device, the HemoCue 801, has been validated for the measurement of haemoglobin in three important fish species for the Nordic aquaculture sector by Henze et al. (2025). This new device, which gives readings in less than a second, allows for more frequent and accurate monitoring of fish welfare, leading to better management practices.

Jonathan Roques is supported by FORMAS, the Swedish Research Council for Sustainable Development (2020-00867).