Fish Facts

FISH FACTS: Hook study raises questions


A RECENT laboratory study by a Canadian research group which was published in the peer reviewed scientific journal Fisheries Research in June 2021 has set the cat amongst the pigeons (or more accurately, the barras amongst the baitfish?) when it comes to the long running “fish pain debate”.

The paper entitled “Hook retention but not hooking injury is associated with behavioural differences in Bluegill” found fish that were hooked then unhooked under controlled laboratory conditions did not significantly differ in their behaviour compared to control fish which were not hooked at all. Only fish which were allowed to retain hooks showed any significant change in their behaviour, which included attempts to dislodge the hook against the walls of the experimental chamber, a lower likelihood of leaving a refuge and reduced exploratory behaviour for those which did so. These results indicate that bluegill are resilient to tissue damage from minor hooking injuries to the mouth, and that reported behavioural impairments in fish after release can be explained by the scientifically well known physiological changes from the fight, landing, and/or subsequent handling and air exposure, and now also hook retention.

These results are also consistent with previous work done by Norwegian researchers on Atlantic cod in a 2014 paper entitled “Physiological and behavioural responses to noxious stimuli in the Atlantic Cod (Gadus morhua)”. In that study, they found that besides head shaking (presumably to try to remove the hook), Atlantic cod embedded with hooks in the laboratory exhibited no significant behavioural or physiological differences compared to control fish injected with saline. This makes sense, as inserting a hook is similar to inserting a needle (but without the saline injection). Results which are replicable and consistent between disparate research groups are a fundamental cornerstone of good quality science, as anyone who has read up on the recent “replication crisis” in many fields of science can attest.

However, in contrast to the bluegill study, Atlantic cod exposed to presumed noxious (supposedly painful) acetic acid injection treatments in the 2014 study displayed reduced use of shelter, while hook retained bluegill in the latest study exhibited increased use of shelter, which has also been previously observed in hook retained fishes in the wild in several studies. These inconsistencies between fish behaviour in different studies suggest the behavioural criteria some research groups have been using to “prove pain” in fishes may be species and/or context specific, bringing their scientific validity into serious question. Indeed, when there are no significant differences in the behaviour of fish which have been damaged by hooking compared to control fish injected with saline, and notable inconsistencies in the behavioural criteria being used to allege pain occurs in fish, the whole “fish feel pain” thesis starts to look very wobbly from a scientific perspective.

The authors of the bluegill study (including myself) point out that these discrepancies highlight the need for more studies of this topic by a wider group of researchers. However, in the 7 years since the Atlantic cod study found that hooking was not painful “possibly reflecting a resiliency to tissue damage in the mouth area related to the tough nature of the Atlantic cod diet”, it’s interesting that it is seldom cited (read: ignored completely), by the “pro fish pain” lobby which are now attacking various fisheries and aquaculture practices in unprecedented fashion. Perhaps these studies are an inconvenient truth for some, but they exist, and assertions by the pro fish pain groups that “scientific concensus” has been attained on this topic are complete nonsense.

As an aside, if you were wondering where these claims for concensus come from, they are actually based on a random assemblage of unreviewed letters submitted to a publication called “Animal Sentience”, a forum which was established by animal rights interests to publish opinion on animal rights matters. Hardly a balanced and informed forum for determining “scientific concensus”! The facts are: claims that are now widespread on the internet and in various publications that “fish pain” experiments with acetic acid are somehow relevant to angling are simply not supported by the available data. In all the various experiments where fish exposed to acetic acid injections allegedly showed behavioural signs of “pain” (behaviours which have mostly not been proven replicable by other research groups), the control fish injected with saline behaved normally. We now have two separate studies showing that inserting a hook is similar to inserting a needle and injecting saline, thus the logical conclusion is angling is the equivalent of the control in the various acetic acid studies. This means those same acetic acid studies back up the bluegill and Atlantic cod studies and actually demonstrate that trauma due to hooking whilst angling is not painful to fish! What a contrast to the “angling is painful” messages which now pervade the internet and we are hearing more and more of each day.

Various animal rights interest groups (and some scientists) are adamant that fish are highly intelligent and emotional sentient beings with surprising mental capabilities. As a sceptical scientist and keen student, I examined several of the studies being used to back up these claims. Scientists study numerous aspects of fish behaviour, but as an example I was intrigued by a study published in 2014 that generated claims in the media that fish can count as well as dolphins, monkeys and a one year old child. The headline result of this often quoted study “Extensive training extends numerical abilities of guppies” was that guppies could count to 4. However, reading the actual study found that this ability was achieved only by a tiny number of fish (5 out of 8) after intensive training, and the researchers discarded many other fish which could not meet the grade before the trial even started because they “could not accustom to the procedure”. This shows a large tendancy towards experimental artefact, bias and exaggeration of the results of this experiment. The actual evidence is certainly at odds with the headline claims that “fish are as smart as your toddler”. Instead, these results show that fish can learn, which of course is certainly not a new finding, yet the hype remains and is actively promulgated by activist groups.

This tendancy to hype and “spin” the results of studies of marginal scientific merit has increased markedly in recent years, as has the emergence of activist “documentaries” like the recent Seaspiracy show on Netflix, which was widely critiqued because it contained so many falsehoods in its ultimate aim to serve its director’s vegan activist agenda. Indeed, Seaspiracy and other activist campaigns of similar ilk by animal rights groups masquerading as animal welfare advocates would be better described as docudramas, or most accurately, pure docufiction designed to be amplified by social media to drive their activist agendas. A recent article “Misinformation in and about science” explores how hype, hyperbole and publication bias are rife in the modern world, and the recent fish pain and fish cognition literature is a classic example of exactly that. Policy makers who these days seem all too willing to jump on bandwagons where the quality of the scientific basis for decision making is neglected, need to take heed. More careful and considered science based management approaches are needed for the various aquatic animal welfare issues that occur in fisheries and aquaculture. Remember that good science is usually slow science – it takes time to sort things out properly.

For a 2014 overview of the fish pain debate, see:

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