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dnalex

How Goldfish Distinguish Between Food versus Substrate (Sand/Mud/Gravel)

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Hello all, I thought I'd post this review article on goldfish physiology, published in 2008, for your reading pleasure. It concerns the question of how goldfish can find food in the habitats in which their ancestors came from, and where some of them are now. In these habitats, the natural order of things is that they will get food anywhere they can get, and this many times will be on the river/lake/pond bottoms, where there is detritus, sand, gravel, muck, you name it. The water may not be all that clear either. So how do they find food?

Here are some salient points:

- Goldfish have evolved to be suck up all kinds of stuff with their food from the river/pond/lake bottoms, and then they sift they out in their mouths, whereby they retain the food and spit out (most of) the yucky stuff, including things like sand, mud, gravel, and other very fine particles.

- The goldfish digestive system is designed for this particular task, and about 20% of the goldfish's total brain mass is dedicated to taste, and hence sorting out the foods versus other things.

Here are some excerpts from the review,

Casual observation of goldfish, as many of us do when we are children, admits of no obvious complex behaviors that may be served by such an elaborate neuronal machine. Indeed, my own initial observations of goldfish led me to the conclusion that they barely have any behavior whatsoever. If one sprinkles food along the top of the water, the fish pick off individual food particles, apparently using vision in a fashion similar to almost all other diurnal animals. But if one waits for the food to sink to the bottom, a more interesting and subtle behavior can be observed. The food tidbits mix in with the substrate – gravel, sand or mud. The fish orients head downward and vacuums up the mixture. The fish then manipulates the mix in the mouth, finally spitting out what was just taken in. Such is the appearance. But more careful observation shows that what the fish spits out is only the substrate; all the food has been retained. This task is tantamount to our placing a small candy into a handful of fine gravel and popping the whole handful into one’s mouth. The task then is to sort out the candy from the stones. We can do this, albeit slowly, and by using a serial consideration of each potential object in the mouth. Goldfish use a different strategy.
The essential feeding behavior of goldfish and related carps is to suck up substrate, food, etc. into the oral cavity, array the mouthful in the space between the palatal organ and the gill arches, and then to trap food particles between the palatal organ and branchial apparatus that forms the floor of the oral cavity. By means of backwashing and rinsing, the fish can then retain the food particles while ejecting the inorganic substrate material (Callan and Sanderson 2003; Sibbing et al. 1986).

Here's the full article

http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2543128/pdf/nihms65972.pdf

So, as you can see, it is natural for a goldfish to forage for food by taking large gulps of substrate, and then through its highly specialized system, to sift through the junk (in its mouth) and retain the goodies, while spitting out the junk. Essentially, the goldfish gulps in muck, sand, gravel and other things to find food. It's in their biology.

Don't underestimate our awesome fish of choice. They have some amazing tricks, well, up their mouths. :rofl :rofl :rofl

I hope you find this article as interesting as I did. Thanks! :)

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Very cool!!! I always wondered how they figured out MM FOOD vs. EWW POOP.

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Very cool!!! I always wondered how they figured out MM FOOD vs. EWW POOP.

They dedicate an entire 20% of their brains to this task! :rofl :rofl :rofl

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Can you imagine how amazing a bowl of peach cobbler and ice cream would be if you had 20% of your brain working on how good it tastes?

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Can you imagine how amazing a bowl of peach cobbler and ice cream would be if you had 20% of your brain working on how good it tastes?

I can imagine how humongous I would be! :rofl

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Great read, Alex :D Thanks for sharing!!

Can you imagine how amazing a bowl of peach cobbler and ice cream would be if you had 20% of your brain working on how good it tastes?

I can imagine how humongous I would be! :rofl

OMG me too!!!! :rofl

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Very interesting :) I see mine vacuuming the sand for food particles all of the time. I wish they could vacuum the rest of the house :rofl

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What a great article! The vagal taste system described by the author is amazing.

Thomas Finger (the author) writes in one of the concluding paragraphs,'While the model we present above has the advantage of being simple, unfortunately, it is also simplistic. The behavior is far more complex than the simple “where it tastes good, hold on” paradigm described above' (p. 7).

This makes me think about Whale's behavior when he ate fermented sauerkraut for over a week then stopped eating it. Was his eating behavior due to signals from his brain telling him to stop because the probiotic benefit he was getting was no longer necessary and why continue eating the nasty tasting stuff? Could his vagal taste system be that nuanced? Possibly with 20% of the neural tissue in his brain being dedicated to his taste system. Pretty cool to think about.

Thanks for sharing this article!

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What a great article! The vagal taste system described by the author is amazing.

Thomas Finger (the author) writes in one of the concluding paragraphs,'While the model we present above has the advantage of being simple, unfortunately, it is also simplistic. The behavior is far more complex than the simple “where it tastes good, hold on” paradigm described above' (p. 7).

This makes me think about Whale's behavior when he ate fermented sauerkraut for over a week then stopped eating it. Was his eating behavior due to signals from his brain telling him to stop because the probiotic benefit he was getting was no longer necessary and why continue eating the nasty tasting stuff? Could his vagal taste system be that nuanced? Possibly with 20% of the neural tissue in his brain being dedicated to his taste system. Pretty cool to think about.

Thanks for sharing this article!

With 20% of their brain being dedicated to the sense of taste and related issues, I think it can definitely be that nuanced. :)

I will be presenting more of these articles on goldfish and their related cousins on a regular basis. We've come far from the days of thinking that goldfish has a memory of a few seconds. But, as with any system, biological or otherwise, the more you delve in, the more you find that you don't quite know nearly enough.

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Goldfish are such complex, beautiful creatures!

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They do have tricks up their mouths, don't they :rofl2

Great article and helpful analysis Alex :alex

Thanks :)

Edited by Flipper

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When I observed goldfish sifting through the substrate, it always brought back a memory from childhood. An old farmer gave us some sunflower seeds. We cracked the shells with our teeth then ate the kernel. He told us we were doing it the wrong way and proceeded to throw a whole handful in his mouth, chew them up, spew out the shells, and throw in another handful. He swore he swallowed all of the kernel and spit out all of the shell. I tried, but never mastered that skill.

So it was quite obvious to me that goldfish were doing the same thing, LOL.

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Very cool!!! I always wondered how they figured out MM FOOD vs. EWW POOP.

They dedicate an entire 20% of their brains to this task! :rofl :rofl :rofl

I wish Riley used even 2% of her brain for this. :doh11: FOOD vs. RABBIT POOP :Scoff:

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Gotta love science ;)

thanks for posting this alex. Just watching our fish we can see that they are obviously designed to handle substrate when necessary, and it's nice to hear the concrete evidence behind this observation. I actually don't think I have ever seen my fish spit out a piece of food when going through this sorting process. There is certainly a bit of substrate that inevitably gets swallowed during this process, but it makes sense to me that these fish are designed to handle a bit of that in their digestive system, just considering that the natural environment is a sandy, mucky place that probably requires even more digging around for food than our well maintained aquariums ;)

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Gotta love science ;)

thanks for posting this alex. Just watching our fish we can see that they are obviously designed to handle substrate when necessary, and it's nice to hear the concrete evidence behind this observation. I actually don't think I have ever seen my fish spit out a piece of food when going through this sorting process. There is certainly a bit of substrate that inevitably gets swallowed during this process, but it makes sense to me that these fish are designed to handle a bit of that in their digestive system, just considering that the natural environment is a sandy, mucky place that probably requires even more digging around for food than our well maintained aquariums ;)

I agree, Jess. We know now that there is such a thing as ingesting too much sand. I don't know why it happens, but it can happen. In such cases, it might make sense to move to no substrate or a different kind of substrate.

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I can imagine the vagal taste system being damaged due to being sick or something else, and that could result in ingesting nonfood stuff.

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I can imagine the vagal taste system being damaged due to being sick or something else, and that could result in ingesting nonfood stuff.

It could be that, but I think the system is not designed to be perfect, in that every non-food particle will be rejected.

The goldfish digestive tract is not based on efficiency (lacking a true stomach) and is rather based on pushing through large quantities of food through the gut. In this regard, particulates like sand and dirt actually aid in digestion in grinding the food down. Sand was found in the guts of carp when the gut contents of these fish were examined.

Here is another interesting read, although please be forewarned that it is not a scientific reading. I am linking because I thought the author did a great job talking about carp (including koi and goldfish) digestion. :)

http://www.watergardenersbible.co.uk/pond-food-feeding/digestion-in-koi-and-goldfish-stomachless-fish/

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I can imagine the vagal taste system being damaged due to being sick or something else, and that could result in ingesting nonfood stuff.

It could be that, but I think the system is not designed to be perfect, in that every non-food particle will be rejected.

The goldfish digestive tract is not based on efficiency (lacking a true stomach) and is rather based on pushing through large quantities of food through the gut. In this regard, particulates like sand and dirt actually aid in digestion in grinding the food down. Sand was found in the guts of carp when the gut contents of these fish were examined.

Here is another interesting read, although please be forewarned that it is not a scientific reading. I am linking because I thought the author did a great job talking about carp (including koi and goldfish) digestion. :)

http://www.watergardenersbible.co.uk/pond-food-feeding/digestion-in-koi-and-goldfish-stomachless-fish/

Alex, thank you for the link. So cool to read about goldfish not having a true stomach! I've read that on this forum, but I enjoyed reading about in more detail. Thanks again!

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I can imagine the vagal taste system being damaged due to being sick or something else, and that could result in ingesting nonfood stuff.

It could be that, but I think the system is not designed to be perfect, in that every non-food particle will be rejected.

The goldfish digestive tract is not based on efficiency (lacking a true stomach) and is rather based on pushing through large quantities of food through the gut. In this regard, particulates like sand and dirt actually aid in digestion in grinding the food down. Sand was found in the guts of carp when the gut contents of these fish were examined.

Here is another interesting read, although please be forewarned that it is not a scientific reading. I am linking because I thought the author did a great job talking about carp (including koi and goldfish) digestion. :)

http://www.watergardenersbible.co.uk/pond-food-feeding/digestion-in-koi-and-goldfish-stomachless-fish/

Alex, thank you for the link. So cool to read about goldfish not having a true stomach! I've read that on this forum, but I enjoyed reading about in more detail. Thanks again!

You're welcome. :)

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Thank You dnalex. Very interesting reads. Can't wait for your next article. I appreciate it very much :)

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Awesome!! Thanks so much!!! XD I always figured they just did that, but it's really fun to learn all the specifics. :P

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Amazing. Thank you for posting this.

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