Neurobiologists have long recognized that fish have nervous systems that comprehend and respond to pain. Fish, like “higher vertebrates,” have neurotransmitters such as endorphins that relieve suffering—the only reason for their nervous systems to produce these painkillers is to alleviate pain.
Yes, fish feel pain
The American Veterinary Medical Association states in their guidelines for euthanizing animals that fish “should be accorded the same considerations as terrestrial vertebrates in regard to relief from pain.”
“Fish do feel pain. It's likely different from what humans feel, but it is still a kind of pain.” At the anatomical level, fish have neurons known as nociceptors, which detect potential harm, such as high temperatures, intense pressure, and caustic chemicals.
The nociceptor then sends an electric signal to the brain, where the psychological experience of pain manifests. Fish have numerous nociceptors in their mouths and thus getting hooked is certainly a painful experience for them.
Fish do not have a neocortex — only mammals do. Thus, according to this reasoning, fish do not feel pain. This is reassuring to many people who eat fish or catch fish for sport.
Though it has been argued that most invertebrates do not feel pain, there is some evidence that invertebrates, especially the decapod crustaceans (e.g. crabs and lobsters) and cephalopods (e.g. octopuses), exhibit behavioural and physiological reactions indicating they may have the capacity for this experience.
Scientists differ on the degree to which fish can have consciousness. Some researchers argue that they cannot have consciousness as their brain is simple, lacking a cerebral cortex, and they have little capacity for learning and memory, a very simple behavioral repertoire, and no ability to experience suffering.
The differences in acidity and dissolved oxygen, not to mention all of the fat, proteins, carbohydrates, and other minerals in the milk that might clog the creature's gills, would quickly spell trouble. The animal would likely die within minutes, if not sooner.
Given that plants do not have pain receptors, nerves, or a brain, they do not feel pain as we members of the animal kingdom understand it. Uprooting a carrot or trimming a hedge is not a form of botanical torture, and you can bite into that apple without worry.
Norway might have considered banning the use of live worms as fish bait if the study had found they felt pain, but Farstad said ``It seems to be only reflex curling when put on the hook ... They might sense something, but it is not painful and does not compromise their well-being.
Yes, fish experience both physical and emotional pain. Scientists say that it's likely a different type than what humans experience, but it's pain nonetheless. Fish have nerve cell endings called nociceptors, which alert their bodies to potential harm such as high temperatures, intense pressure, and harmful chemicals.
It is likely to lack key features such as 'distress', 'sadness', and other states that require the synthesis of emotion, memory and cognition. In other words, insects are unlikely to feel pain as we understand it.
Insects do not have a visual cortex, for example, but there is no doubt that they can see. It is thus possible that insects may also experience pain, but underpinned by different neural circuits than mammals (e.g., multiple realizability and related theses: Chittka et al., 2012; Mallatt and Feinberg, 2021).
Fish have gills that allow them to “breathe” oxygen dissolved in the water. Water enters the mouth, passes over the gills, and exits the body through a special opening. This keeps an adequate amount of water in their bodies and they don't feel thirsty.
Research has clearly shown that lobsters, crabs, and other crustaceans can and do experience pain. Scientists have shown that their reaction to painful stimuli is more than just a reflex response and instead, they learn from painful stimuli and change their behavior.
Fish will get the occasional itch and seeing a fish flick against a rock isn't necessarily a cause for alarm. But if it's performed with any regularity, it's worth checking for ammonia or nitrite and chlorine in untreated tap water, as these can cause irritation.
Roots of plants are exquisitely conscious and aware of self and not-self and engage in sophisticated interactions with a wide range of living organisms. The plant roots enter into symbiotic relationships with bacteria, fungi, and communicate with other plants that are highly sophisticated.
Plants do not have pain receptors, which is a critical sign that plants do not experience pain in the same way that animals do.
Oysters have a small heart and internal organs, but no central nervous system. Lack of a central nervous system makes it unlikely oysters feel pain, one reason some people who otherwise are vegetarians comfortable eating oysters. Some oysters have two sexes, but all have both eggs and sperm.
The short answer is no. Fish don't get sad over the death of their tank mates like humans do. However, they exhibit certain behaviors that lead people to speculate that they are mourning the death of their finned friends.
In some liquids, such as tea, a fish might find very similar levels of oxygen, as tea is largely composed of water. However, the other substances in the water—even on a molecular levels—would be foreign to the body of the fish, and the concentrations would be different than what their body was adapted to handle.
Coffee doesn't have the same level of oxygen as water, so the fish won't be able to breathe as well. So really, the effects will still be potentially damaging for the poor fish, even if the cup they get doused in contains decaf coffee. The liquid is still altering the pH and oxygen levels in the tank.
Non-sentient animals would then include sponges, corals, anemones, and hydras.
There has recently been increasing evidence demonstrating that fish can discriminate between familiar individuals based on facial characteristics (i.e., true individual recognition) and can even identify individual humans faces (e.g., refs. 22–29).
Scientists have just observed a thought swimming through the brain of a live fish, and that thought concerned getting something good to eat. Fish and other wild animals appear to think a lot about food: how to obtain it and what to consume.