Issue 11 / May 2016

Consider the fish. What do we know about pain in animals?

a portrait of Victoria A. Braithwaite, Daniel M. Weary, Paula Droege by Sonja Kastilan

Bambi is cute - even a movie star. But who cares about a fawn when a clownfish named Nemo goes missing? Although lacking fur and a snout he awakens empathy in humans, and his animated film adventures have recently transformed fish into appealing and popular figures – though we otherwise regard these creatures as cold, mute and benumbed (preferring our herring wrapped around a pickle and giving hardly a thought as to their possible suffering).      

Many of us can perhaps generate enthusiasm for seahorses and boxfish or appreciate the fight put up by a carp when it’s hooked. But generally speaking, fish have it pretty tough. We encounter them as pickled herring, fish sticks, smoked salmon or canned tuna, and we tend to forget that these tasty morsels were formerly living vertebrates – that whether festooned with orange and white stripes or just possessing the standard silvery scales, fish are capable of a wide spectrum of sensations. But was Charles Darwin correct in assuming that the lower animals can even have feelings similar to those of humans – feelings of joy and pain, happiness and sadness?      

Their aquatic way of life makes fish alien creatures to us; however, they can accomplish astounding things. For instance they crack open shells with the help of hard rocky outcrops, using them as tools. And they are by no means mute. They grind their teeth, growl or communicate in other ways such as changing their color, and their eyes convey presumably more then we suspect. “Only they can’t talk to us about their emotions, which of course makes it difficult to recognize their abilities and undertake such experiments that would directly measure their experience of pain,” says Victoria Braithwaite, a behavioral scientist from Pennsylvania State University whose work in this area is a labor of love. At the Wissenschaftskolleg she is leading a Focus Group devoted to the subject of Pain, this group includes Daniel M. Weary, a behavioral scientist from the University of British Columbia in Vancouver, and Paula Droege, a philosopher also from Pennsylvania State University. 

Pain means more than mere sensory perception of a potentially damaging mechanical, thermal or chemical stimulus. It also means a subjective unpleasant feeling that leads people to change their behavior and thus prevent injury. But these feelings are private and hence hard to assess, especially in animals that are very unlike us. Braithwaite and her colleagues in Berlin are presently tackling the question of if and how we can assess this felt experience of pain in fish and other animals. Says Braithwaite: “We are attempting to distinguish the various stages of perception and conceive experiments to see how animals react, learn, remember and subsequently evaluate whether a certain environment is potentially dangerous for them.” 

Identifying this felt component of pain has strong ethical implications. The heart of concerns about animal welfare involves their experiences of negative and positive feelings – the pains and pleasures of life – so knowing, for example, when a fish feels pain will help inform ethical discussions about types of procedures that animals should be exposed to. Concerns about fish welfare have already led to improvements in methods used to slaughter some farmed fish, but billions of wild caught fish are killed using methods that may cause intense suffering. 

Do reactions to pain occur consciously or unconsciously? And what function befits this consciousness? What advantages does it offer? These are questions that preoccupy Paula Droege, and like the two other members of her Focus Group, she regards a multi-disciplinary discourse as important to doing justice to the subject of pain. Particularly since the debate about consciousness is mostly based on human beings and their sensations, we may focus on the constant process of self-reflection and mulling over thoughts about ourselves and the future instead of more simple forms of experience. It is more difficult to take on the perspective of whatever animal and accept that not only are humans in possession of consciousness but so too fellow-mammals and perhaps even other creatures. 

“When we become conscious of something, this permits us a certain flexibility in our actions,” says Droege in explaining why an understanding of time plays an important role. “We recognize the events in present time and can learn from them and thus adapt to our environment.” The past influences our behavior; consciousness helps us to make a choice. But the degree to which this applies to other living beings is among other things dependent on a creature’s evolutionary developmental stage. Not every animal contemplates tomorrow. Droege says that among other projects they wish to use their time at the Wissenschaftskolleg to create a kind of research program whereby science both challenges scholars and offers them procedures to follow in solving certain problems pertaining to those challenges: “We need tests to compile data that will allow us to verify our theses regarding consciousness and pain.” But there is probably no single experiment that would have general validity for every species.        

Researchers regard development of the sensation of pain as a beneficial survival mechanism. It is improbable that it should have emerged suddenly in human beings. There must have been preliminary stages, opines Victoria Braithwaite, for ultimately we are part of the evolutionary process. The behavioral scientist is persuaded that fish manifest feelings and thus register something akin to pain, “though not in the same sophisticated manner as we humans.” But for those who desire to kill a fish without subjecting it to undue torment, she tenders a sole piece of advice – do it as quickly as possible. A fish’s brain is relatively simple, and skeptics often make neurobiological distinctions between the anatomy as well as the physiology of humans and fish so as to deny the latter any capacity for suffering. They are also unpersuaded by observed changes in behavior, which is precisely the basis on which Braithwaite renders her judgment: “Fish change their plans so as to evade disturbing irritants – they’re flexible.”   

That there are indeed receptors in fish is insufficient evidence; crucial here is just how the external stimuli affect their behavior. Together with her colleagues, in a series of experiments, Braithwaite was able to show that rainbow trout react to acetic acid and bee venom. She describes the observations they made: “Headaches disturb our ability to concentrate, and the fish behaved differently as well and approached an object that they would have otherwise avoided.” Morphine was able to restore the fish’s normal state – similar to how a pain reliever for headaches would help humans. Braithwaite and her team conduct studies in natural bodies of water and carry out additional tests with fish in laboratory experiments: “We give careful thought to exactly what we will be doing and how many we will catch because there is no going back for the fish.” They were also able to observe that fish can react in a frustrated manner. For instance when they failed to receive their usual food they changed their tempo; they were visibly disconcerted by the fact that it was of lesser quality or volume.  

Now and then Braithwaite herself harbors a feeling of frustration due to the fact that especially neuroscientists have not been persuaded by the data. And also because fish are still underestimated even though there are examples of two species that cooperate with one another. In the Red Sea there are groupers and giant morays that form successful hunting communities based on communication and coordination. This is a fascinating example – yet it remains difficult for people to ascribe any feeling to the perceived expressionless faces let alone grant any kinship to humans.    

The more that an animal appears similar to us, the more we feel compassion for the creature. We place the chimpanzee above the rat, the fish above the cockroach or some other insect. “The value that we attribute to a fellow creature influences how we assess their abilities and sentience,” says Daniel Weary – and he takes a page out of the history of medicine: With the emergence of anesthesia, doctors of the time did not apply it in equal measure to all their patients but only to those for whom they felt it was important. Similar judgments have been passed regarding the suffering of animals, these judgments changing with the passage of time. For example horses and cattle were always granted respect as beasts of burden, whereas cats and dogs now enjoy a higher status than earlier.    

But Weary regards another question to be of greater import than that of whether animals feel pain: what exactly causes them to suffer? The heart of the matter for Weary, who for years has involved himself with farm animals, is their well-being: “What does it mean for an animal to have a good life?” Dog owners and farmers quickly recognize when the behavior of an animal changes or it experiences shifts in mood.     

The zoologist is hardly advocating a world without farm animals and pets – he’s simply doing his utmost to insure that they are treated as well as can be possibly expected. Ultimately the relationship between animals and their owners is based on a long cultural history, and this context needs to be considered when developing improved ways of caring for animals. His research is in service to society: “We help to better the conditions of husbandry by attempting to understand what animals need, what is best for them and what inflicts the least amount of suffering when it is unavoidable, for instance with medical procedures.”     

Investigations at the molecular level are insufficient in recognizing discomfort, stress, fear, pain and suffering – for example an increased concentration of stress hormones in the blood can indicate agitation in a positive sense. “Experiments must therefore be refined so as to discover an animal’s specific preferences and dislikes. And it is also important to understand what suffering means for different animals, particularly when their biological requirements and sensory abilities are very different to our own,” explains Weary, whose knowledge of such experimental set-ups is highly valued by Braithwaite and Droege. For instance, to better understand the motivation of dairy cow to access pasture, cows were trained to open a weighted gate. The maximum weight the cows were willing to push could then be compared to the weight they were willing to push when they were hungry. The study showed that cows would ‘work’ very hard to go outdoors, pushing about the same weight as they are willing to push to access fresh feed after their morning milking. “Nobody would deny cows their breakfast but they are often prevented from grazing in the pasture,” says Weary, thus throwing into question a present-day practice on many farms. In other work Weary and his students have developed methods of assessing mood states in animals by testing their responses to ambiguous stimuli. They have found that dairy calves will show a negative judgment bias (i.e. treat a neutral stimulus as if it was negative) when experiencing the pain in the hours after dehorning (a common farm procedure). Interestingly, calves showed a very similar judgment bias in the hours after separation from their mother at weaning, suggesting some similarity in the effects of emotional and physical pain on mood in animals.    

Many animals suffer under a loss of control, while others incur suffering as a result of isolation. Not only their evolutionary history but their social structure – e.g. herd animals as opposed to solitary ones – and life expectancy have an impact on how animals behave and experience pain. These factors must be taken into consideration. “It is only when we understand their behavior that we can make and test interesting prognoses,” says Braithwaite, who characterizes fish as sentient but who still remains unpersuaded with regard to crustaceans; and she sees a great challenge for scientific research in the case of cephalopods such as the octopus. Charles Darwin on the other hand was less circumspect: He regarded it as a fact that the lower animals are affected by the same feelings as we humans. 

More on: Pain
Images:© Maurice Weiss