Do goldfish have a stomach?

2012/08/31 at 08:00 | Posted in Veterinary Fish Medicine | 9 Comments

Why raise such a question?

I was watching an episode of “Tanked” (Animal Planet Discovery Show) and there was a pop-quiz that I hate to admit it, but I got wrong…. well… according to them anyway.

The question was… which of these fish do not have a stomach?…. The answer they gave was Goldfish. And so it was proposed that goldfish need very much more regular feeding than twice a day.

Whether a goldfish has a stomach has been a subject for debate on may fish forums on the net – just Google “tanked tv show goldfish stomach” and you’ll see.

In animals, the stomach is located between the oesophagus and the duodenum (the most anterior part of the small intestine).

Many texts and scientists (and the producers of “Tanked”) believe that goldfish do not have a stomach. In a reply by Dr Brian Jones, he pulled out this excerpt:

About 15% of teleosts, including cyprinids, have no stomach and no region of low pH or pre-digestion. Anterior portion of intestine has some storage function, intestine in these species is usually very long compared to, say, a trout (Rombout, et al. 2011. Teleost intestinal immunology. Fish and shellfish immunology 31:616-626.).

I looked up Balliere’s Comprehensive Veterinary Dictionary for the definition of stomach and this is what I found – the curved, muscular, saclike structure that is an enlargement of the alimentary canal between the oesophagus and the small intestine.

Then I carefully dissected the carcass of a formalin-fixed goldfish I had spare on my shelf (as you do) to see whether the goldfish has a stomach. I found that there was certainly a saclike distension to the anterior part of the alimentary tract, immediately caudal to the oesophagus.

So what would you call the dilated portion of the gut immediately posterior to the oesophagus in the goldfish?

In birds, you have a crop, a proventriculus (the secretory stomach) and a gizzard (the muscular stomach) between the oesophagus and duodenum.

Ruminants are known to have 4 stomachs, they have the rumen, reticulum, omasum and abomasum between the oesophagus and duodenum.

In an alpaca, you have compartments 1, 2 and 3 between the oesophagus and duodenum.

So, if you do not call the structure (arrow) in the diagram a stomach, what would you call it?

“Intestinal bulb” was proposed.

I may have to accept defeat on a technicality….

I open it up to you now for debate…

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9 Comments »

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  1. I personally would call this a stomach, however I understand the debate and would agree to disagree as to whether a goldfish has a stomach or not.
    What I would be more dogmatic about is that a goldfish intestinal tract with their small or non existent stomach require that dry foods be moistened prior to feeding to prevent digestive problems, including Aeromonas infections.

    BTW, great post and I will be forwarding it to a friend, as I am sure he could use it to link to in one of his articles

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  2. Very interesting. But as a goldfish owner, what interested me on “Tanked” was the assertion that, due to a lack of a stomach, you should feed your goldfish frequently. So, stomach, no stomach, or “bulb”, should I be feeding Senor Pescado twice a day? Once a day? Once every other day? Please advise!

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    • That’s correct. Goldfish should be fed two or more times daily. How much to feed? About 1% of their body weight daily.

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      • Wright or wrong I have always fed my 4 year old goldfish once every 3 to 4 days. It seems “happy” and alert and growing at a reasonable rate. As a result of reading this I’m tempted to increase feeding times but am loathe to change a practice that evidently works.

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      • Once every couple of days is ok during the cooler months, and excess feed can pollute the tank and kill fish.
        Make sure your tank has adequate filtration because your comments give me the impression that he might be in a bowl.

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      • Hi. He is in a 6 gallon tank with intetnal biological and mechanical filter, gravel substrate and live ,hardy plants. I would like to get him a bigger tank but am fearfull of leaks due to a tropical ” disaster” I had ten years ago when a 20 gallon tank disintigated flooding the apartment below. We’ll see, feint heart never won fair maiden. :-)

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      • If you do setup a new tank, ensure that you keep your current biofilter alive and install it in conjunction with the new filtration to avoid ‘new tank syndrome’.

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  3. I think a low pH is critical in the definition of stomach.

    The intestinal tract can’t be constant in width. It varies in
    radius. You can’t call every enlargement of the intestine a
    stomach. Otherwise, the large intestine in mammals would
    have to be called a stomach. There are also various sacs
    attached to the intestine.

    A stomach in mammals has a low pH. The environment
    in a stomach is highly acidic. This allows certain enzymes
    to digest fibrous proteins such as collagen. Therefore,
    the low pH has a well defined function.

    Saying that a goldfish has no stomach allows
    one to answer the following question. Why are goldfish
    considered dirtier than other aquarium fish? One can
    answer that it has not stomach. Because the goldfish
    has no stomach, it can’t completely digest meat and fiber.
    Therefore, it produces more poop per pound of meat.

    If one goes with the low pH definition of stomach, then
    one can easily find other animals without a stomach. None
    of the carp have stomachs in the sense of low pH. This is
    because they mostly feed on microscopic algae, which
    doesn’t need to be digested with acid. Note that the goldfish
    is a type of domesticated carp. The platypus also doesn’t
    have a stomach.

    The enlargement of the intestine in carp is sometimes called
    a digestive bulb. However, it can’t digest the same type of
    food as a mammals stomach. Therefore, I don’t think it
    should be called a stomach.

    The pH is easy to measure. Furthermore, low pH has a
    specific function in terms of digestion. Therefore, I suggest
    that low pH be used as a defining characteristic of stomach.

    Like


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