Table 2.

Examples of outstanding research questions that exist in each Research Gap identified herein, as informed by the Scientific Committee, Code Development Committee, and the authors' perspective as fish welfare researchers.

Biodensity	▪ What biodensities are preferred by different salmonid species and life-stages? ▪ How does social behavior change throughout the entire salmonid life cycle? Are these patterns species-specific? ▪ What is the relationship between fish body size and optimal biodensity? ▪ Do patterns and relationships identified in the current biodensity literature scale up to large production systems? ▪ How does biodensity affect salmonid recovery from acute stress? ▪ For different welfare-relevant pathogens, how does biodensity contribute to pathogen transmission?
Health monitoring and management	▪ What are the sub-lethal effects of sea lice infestations on salmonid welfare, and at what threshold number of lice per fish do they occur at welfare-compromising levels? ▪ What are the welfare impacts of repeated exposure to chemical therapeutants for managing sea lice infections? ▪ How do alternative sea lice treatment methods (e.g., thermal and physical de-lousing, etc.) impact salmonid welfare? ▪ How does the introduction of cleaner fish species to a given enclosure impact the welfare of captive salmonids? ▪ What are the potential areas of concern for cleaner fish welfare?
Feed quality and management	▪ Do fish experience hunger as an aversive affective state? ▪ If hunger is aversive to fish, how motivating is it? ▪ How might the aversiveness of hunger interact with different social dynamics (e.g., dominance hierarchies) to impact welfare? ▪ What protein alternative is best for the welfare of different salmonid species? ▪ What period of feed restriction or withdrawal is appropriate (i.e., does not compromise welfare), and how does it change with different environmental conditions?
Enclosure design	▪ What types of if environmental enrichments do farmed salmonids prefer at different life-stages? ▪ What types of environmental enrichment positively impact fish welfare at different life-stages? ▪ What types of environmental enrichment are feasible to deploy on-farm? ▪ What effect does the spectral composition of light have on fish welfare at different life-stages? ▪ What effect do differing photoperiods have on fish welfare? ▪ How is light intensity distributed in differing tank depths and how might this affect fish welfare?
Slaughter and euthanasia	▪ What brain region(s) is/are responsible for consciousness in fish? ▪ How do we measure brain function in fish? ▪ At what point does unconsciousness occur during differing slaughter and euthanasia methods? ▪ What is the cause of death in slaughter and euthanasia methods (e.g., ice slurry slaughter and electrical or percussive stunning)? ▪ Are there more humane methods of slaughter and euthanasia than presently available?