Poetgrrl’s post below reminds of something I’ve always wondered about. I read somewhere that some shellfish such as oysters, clams, scallops, etc. don’t have brains. How is it that they know to flee (in their clumsy way)from known predators (especially since they don’t have eyes). And considering that oysters are often eaten raw, do they feel pain? If not, why do they have such smooth inner shells and form pearls to protect themselves from an irritant. If they feel pain, why don’t they react when pierced with a fork or cooked on the half shell?
A brain is a large lump of nerve tissue. Most mollusks make do with a less centralized system, having a series of ganglia controlling reactions to environmental stimuli. It’s not like a clam has a wide range of behaviours which need coordination. (Scallops have many eyes, most of them a pretty blue.)
Once the shell is breached, an oyster or scallop is pretty much out of alternatives, so it is not surprising that they have no response to being poked with a fork.
Thank you. Didn’t know that about scallops’ eyes. Still though, does anyone know if it has been determined whether or not they feel pain? (As you can probably tell, I loves me oysters…I just hate to think they can feel it if eat them or have them cooked.)
Here is a nice quote that I send to friends upon getting tenure.
“The juvenile sea squirt wanders through the sea searching for a suitable rock or hunk of coral to cling to and make its home for life. For this task it has a rudimentary nervous system. When it finds its spot and takes root, it doesn’t need its brain anymore so it eats it. It’s rather like getting tenure.”
- Consciousness Explained by Daniel C. Dennett
Seems relevant.
I believe the jury is still out on how developed a brain is required to feel pain. The big debate usually involves fish, with some decrying fishing as a cruel practice, and others conjecturing that fish are incapable of feeling pain. I don’t know what the latest studies show, but a year-two back I read of one suggesting they did not appear to have a brain system analagous to that which in mammals is used for pain sensation.
Anyway, I’d doubt shellfish “feel” anything like pain; their responses are simply reactions to stimulus, and the concept of pain would seem to involve, for one, sentience and the capacity for other “feelings”. Anyway, there wouldn’t be much evolutionary need for pain; if their shell is breached, they’re toast, so why provide a system of negative feedback? It’s just something to waste energy that provides no benefit towards survival.
Very well, I shall continue to enjoy my oysters guilt-free. Thank you, one and all.
You run into troubles with the answer when you try to describe “pain”. Do shellfish feel the exact same sensations we do? Unlikely. Are they aware something is wrong? Of course. How traumatic is it? Unknown so far.
They certainly do have nerves that respond to stimulus, and can tell the difference between say warm/cold water, changes in water chemistry, vibrations, or something crushing their shells. Their are advantages to knowing all these things, or at least having differing reactions to them. You can tickle scallops with a peiece of fishing line so they’ll open their shell, and they’ll slam their shell shut when they feel you poke your finger onto their soft bodies.
I’ve had experience with both the last two; in a lab I poked a scallop that was open, and it slammed shut so hard it cracked it’s own shell around my finger. My partner had to tickle it open since it wasn’t about to let go… unfortunately he was laughing so hard he couldn’t get the line into the little nook for about 20 seconds.
I forget which kind, it may be a kind of cockle or scallop, but this shellfish has enough sensory perception to know when a certain type of star fish touches or gets close to it. We had a demonstration on a beach once where one of these shellfish was placed in a little tide pool along with a starfish (I think it was a sunstar). When the predator started touching it, the shellfish started rapidly opening & closing it’s shell, and basically flaped away from the starfish. That was the only way to get these things to move.
BUT, I say as long as you food doesn’t scream or start squirming away when you stab it, don’t worry about what it might be feeling and eat up!
I don’t know if they feel pain, they may or may not. But lets look at it this way. Say you were confined to a wheelchair because of no feeling below your waist due to a spinal cord injury. You notice that a sharp edge of the wheelchair is digging into your leg. Though you don’t feel any pain you take the roll of duct tape and apply it to the irritant to prevent further injury.
That was just to show how a creature might protect themselves from an irritant w/o pain, not nesseserally the reason the oyster does it.
Applying my four-legs-or-more rule to those things which I eat, most shellfish rate quite low. If they’re lucky, they have a single foot.