The Scottish Parliament at Holyrood, Edinburgh. A parliamentary committee is holding an inquiry into progress made in salmon farming and was last week told that thermal lice treatment caused fish pain.

Fish ‘pain’ evidence to MSPs questioned

A Scottish Parliament committee was last week told that salmon suffer when they undergo thermal lice treatment – but those who say so are doing a lot of guessing, says a veteran scientist


Evidence given to a Scottish Parliament enquiry into salmon farming has been challenged by an experienced Canadian scientist after Fish Farming Expert’s report into the enquiry session was shared on social media by a reader.

Last Wednesday, members of Holyrood’s Rural Affairs and Islands (RAI) Committee heard from University of Gothenburg professor Lynne Sneddon, who said that removing parasitic sea lice from farmed salmon by rinsing them in warm water in a thermolicer caused the fish “pain”.

According to a short biography on the university’s website, Sneddon was “the first to characterise nociceptors that detect painful stimuli on the head of a fish”.

But John Martell, who spent 38 years as a scientist with Fisheries and Oceans Canada (DFO), argues that Sneddon is being too simplistic by telling MSPs that the sensation fish feel is “pain”.


Commenting on LinkedIn, Martell – who has degrees in marine ecology and parasitology, and a doctorate in marine ecophysiology – wrote: “They are doing a lot of guessing especially when it comes to pain. Pain is not only the sensation but how it is perceived. An animal can sense a disturbance in its environment and avoid it but not ‘feel’ what we perceive as pain.

“Fish need to be able to find environments in which they can thrive but that doesn’t mean they ‘feel pain’, that’s anthropomorphising. When terms are used or described, we need to be very careful that not only are we being objective but that they are being perceived as such as well.”

Martell is not the only scientist who disagrees that the stimuli fish receive via nociceptors are the same as feeling pain, or that fish experience pain in the way we understand it, although this scientific divergence was not made clear to the RAI Committee in last week’s evidence session.

Reasons for scepticism

An open access article titled Reasons to Be Skeptical (sic) about Sentience and Pain in Fishes and Aquatic Invertebrates published in the journal Reviews in Fisheries Science & Aquaculture, sets out what its authors say are 10 “scientifically sound and prudent reasons” to maintain scientific scepticism when the topics of sentience and pain in fish and aquatic invertebrates are used to justify inclusion of these organisms in legislation governing their use in the wild, food production or research.

The authors’ 10 reasons to be sceptical about fishes and invertebrates being sentient and feeling pain

1. Changing definitions: deviation from accepted definitions of pain; development of “sentience criteria” based on “confidence levels”. Consequences include encouraging anthropomorphism which invites false equivalence between the experience of animals and that of human pain.

2. Ignoring or dismissing conflicting or contradictory evidence: selectively ignoring data or studies that are inconsistent with the pain hypothesis.

3. Lack of replicable empirical evidence: results “consistent with pain and/or sentience” are not replicable or independently verifiable by multiple research groups.

4. Ad hominem attacks on sceptics: attempts to discredit sceptical scientists who highlight flaws in evidence base. Tactics are said to include attacks in pseudo journals or the popular media, and labelling sceptical scientists as “deniers”, “creationists” or “racists”, along with erroneous claims of “scientific consensus”.

5. Testing of unfalsifiable hypotheses: testing hypotheses that are unfalsifiable negates the fundamental self-corrective aspect of the scientific method.

6. Arbitrary application of criteria: selective application of sentience criteria, for example to decapod crustaceans but not copepods, and to cephalopod molluscs but not bivalves or gastropods.

7. Dilution/devaluation of the welfare concept: if all organisms, even plants, are considered ‘sentient’ based on alleged pain perception, this severely devalues the feelings-based welfare concept itself, because everything (and therefore nothing) is special all at the same time.

8. High risk of unintended consequences: dangers of application of unvalidated welfare criteria to new animal groups under suffering-centred animal welfare legislation frameworks.

9. Dangers of the precautionary approach: invoking the precautionary approach to act before validated operational welfare criteria have been established.

10. The need for organised scepticism and critical thinking: scientists must understand the limitations of the scientific method and must speak up when the scientific method is being misapplied or ignored.

The paper was written by scientists from Australia, the United States, Norway, and Singapore. They include Professor Brian Key, who heads the Neurophilosophy Lab at the University of Queensland (UQ) and spent 25 years on projects to decipher the molecular and cellular bases of brain development and regeneration in fish, frogs and mice. In more recent work, he and collaborator Deborah Brown, Professor of Philosophy at UQ, say that to date they have found that fish and molluscs lack the required neural architecture to feel pain.

The journal article’s authors say they are supporters of animal welfare. “This article is not about choosing between no welfare, and welfare for the animal groups involved,” they write.

A societal choice

“Including more animal taxa under welfare legislation is a societal choice that can be undertaken without firm scientific evidence using the precautionary approach. To do so while avoiding significant unforeseen consequences to food security and human welfare, however, requires reliable, scientifically proven operational welfare indicators that uphold the fundamental principles and standards required of the scientific method.”

According to the authors, the most recent definition endorsed by the International Association for the Study of Pain (IASP) in 2020 describes pain as “an unpleasant sensory and emotional experience associated with, or resembling that associated with, actual or potential tissue damage”.

Not the same

They explain that pain is detected via nociception, defined as the non-conscious processing of noxious stimuli by the peripheral and central nervous system, but that pain and nociception are not the same thing.

“Pain is but one (of many) potential responses to nociception, and merely observing an animal’s detection of and response to a stimulus cannot automatically be interpreted as pain,” write the authors.

They add that some researchers working in the field of fish and invertebrate pain and welfare – including Sneddon - have developed their own criteria for defining and assessing animal pain based on a range of neurological, behavioural and motivational criteria that they believe is consistent with “the idea of pain”.

Shifting the goalposts

“These unconventional definitions ‘shift the goalposts’ considerably, as many of the criteria (e.g., avoidance behaviour) cannot discriminate between nociception and pain, with some behaviours (e.g., those arising from exposure to chemicals in water) not even requiring nociception,” states the article.

“These inconsistencies undermine confidence that interpretation of animal behavioural reactions ‘consistent with pain’ is analogous to how the word pain is defined, used, and understood by humans in accordance with the IASP definition. This has been particularly problematic in the fish and crustacean welfare literature in which any behaviour in response to noxious stimuli is usually interpreted as ‘consistent with pain’, with few, if any, of the several other alternative explanations being considered.”

Progress in Scotland

The Scottish Parliament's RAI Committee is holding the inquiry to find out what progress has been made in implementing reccomendations made in 2018 following an inquiry by one of the committee's previous incarnations, the Rural Economy and Connectivity (REC) Committee.

It has three more evidence sessions this month and resumes its inquiry in September after the Scottish Parliament’s summer recess.

The inquiry timetable is:

  • 12 June: Evidence on farmed fish health; Evidence from the Scottish Environmental Protection Agency
  • 19 June: Evidence on licensing and consenting issues
  • 26 June: Evidence from the Salmon Interactions Working Group
  • 22 to 23 September: Committee visit to a salmon farm
  • 25 September: Evidence from salmon farming industry representatives
  • 2 October: Industry roundtable
  • 9 October: Evidence from the Cabinet Secretary for Rural Affairs, Land Reform and Islands, Mairi Gougeon