How do fish feel pain

Priscilla Winn posed the most difficult question I have yet received at my Internet Web site. She told of her fantail goldfish, badly injured by an animal attack three years ago, and asked me if it feels pain like we do.

The short answer is no. Taber's Cyclopedic Medical Dictionary (recommended for translating biological science writing) defines pain as "A sensation in which a person experiences discomfort, distress, or suffering due to irritation or stimulation of sensory nerves, especially pain sensors." In other words, only humans feel pain. Human awareness of pain itself may add a whole new dimension to the experience, but we can also safely presume the Dictionary's editorial board was staffed by only one species. Rather than try to change the English language, permit me to reword the inquiry: do animals experience hurt-pain without intellectual awareness-like we do? This question is not so easily answered. Comprehending what is felt by a goldfish (with its specialized pain sensors, nervous system, and advanced brain) may best begin with insights into what simpler creatures feel when lacking one or more of "feeling" components.

Bacteria have receptors to many environmental stimuli. If exposed to a noxious chemical, mobile varieties will use hair-like cilia or whip-like flagellae to escape the irritation. This feature is a prerequisite to the definition of life; a reaction more basic than reflex since there is no awareness or even nerves for the signal to travel through. Single-celled creatures detect rather than feel stimuli; therefore, they can detect but not feel hurt. Single-celled pond creatures such as bacteria, algae, and protozoa are like responsive but unfeeling aquatic automatons. There are multiple-celled animals with specialized pain sensors and nerves, yet no detectable central nervous system. Can a mindless animal feel anything, or is it a case of no brain, no pain? About fifteen years ago, researchers presented cotton-wrapped electrodes, soaked in the juices of marine mussels, to hungry starfish. Each time a starfish reached for the experimental morsel, an electrical zap was administered and the creature drew away... then mindlessly reached again. After several hundred repeats, about a third of the starfish lost their taste for mussels. Despite the lack of a brain to accumulate and process memories, shocks penetrated beyond the moment of experience and triggered learning. It is possible that starfish, as well as worms, leaches, and other mindless pond denizens may, in a nebulous manner, experience hurt.

Laboratory studies have shown animals with a totally alien brain anatomy to be capable of experimenting and learning how to manipulate environment in order to obtain food. A moluskan cousin to the snail, the octopus, lacks a spinal cord or anything resembling the sort of brain that humans and goldfish evolved. Nevertheless, this creature betrays revealing glimpses of a mind as nimble as those of our more "intelligent" domesticated pets. The animal has senses to pick up stimuli, nerves to conduct them, and a brain capable of processing these inputs and directing behavioral changes. All parts are present to "feel" hurt, though how the mollusk mind handles this process and colors the experience is any human's guess.

Compared to these creatures, fish are close cousins to human beings. They have brains that very closely resemble ours, even featuring a telencephalon, the region of the cerebrum we humans use for "higher" thought. Of all the animals discussed, fish nerves and brains are most likely to interpret hurt the same way we do.

For example, just as you and I would feel the pierce of a needle more intensely in the skin of the face (with a high density of nerve endings) compared to an arm (with a low density), Priscilla's goldfish probably felt far more hurt from the damaged eye relative to body scratches or split fins. The fish brain may also function to tune out persisting hurt in a manner similar to the human brain. People become partially accustomed to multiple and long term discomfort, persevering with chronic pain that might stagger them if appearing out of the blue. I think it likely that fish become similarly inured; that ache from the injured eye is a constant companion to Priscilla's fantail, but that this chronic discomfort is below the surface of immediate awareness. Empathy with your pet does not have to be a negative experience. If it is tempered with an understanding of what the animal really does feel, as opposed to anthropomorphizing (projecting our human characteristics) empathy can enrich the pond keeping experienc. Imagine the alluring perfume of oxygen-rich water near the waterfall or air stone (studies show that fish can not only detect small elevations of dissolved oxygen, but are attracted to them). Imagine the water-borne equivalent of a latrine reek if you don't feel motivated to make a water change to remedy high concentrations of metabolic waste. Perhaps, though it might be stretching things, an occasional blood worm or frozen cube of brine shrimp can even distract a goldfish from aching war wounds.

By definition fish won't experience pleasure from any more than they experience pain; but if they can feel hurt, why not comfort? As you sit by the pond and watch your aquatic charges, contemplating different aquatic equivalents to pleasure might not just bring real empathy with the underwater world, but add a new dimension to the rewards of pond keeping. www.waterscapes.com/science/fishpain