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Thread: Digestibility & Waste

  1. #1
    Daihonmei MikeM's Avatar
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    Digestibility & Waste

    I often come across comments that a food is "more digestible" as proved by the fact that there is "less waste". I do not understand the supposed connection.

    A fish is largely composed of water. If you have ever had a fish jump out and dry out completely, you know that the dry weight of the fish was a very small percentage of the natural weight. Very little of any dry food is going to be absorbed by a fish through the digestive process. Virtually everything that is consumed will be expelled. So, how can there be a noticeable difference in waste volume?

    Seems to me that there are two possibilities: (1) the food is so nutritious that less dry weight of it is fed [note: not less volume, but less dry weight...some foods are full of air], but I've not noticed people commenting that they feed less of particular foods on a weight basis; or, (2) the waste is just as voluminous, but not as easily observed.

    Wheat germ is often identified as a highly digestible food. In mammals, wheat germ has a mild laxative effect. I expect the same is true of fish. During cool weather this can be very desirable, because we do not want food rotting in clogged-up intestines. However, the reason wheatgerm has a laxative effect is because it contains indigestible fiber, high oil content, and low starch levels (as well as high protein content). It results in less visible waste because the starches which bind waste into visible stools are very low. This does not necessarily mean the fish are getting more nutrient out of the food.

    So, I see the photo on the Saki-Hikari label showing filter mats with less visible waste trapped and I wonder: If the waste is no longer getting captured in the matting, where is it? [If there is 50% less visible waste, are the koi gaining dry weight every meal equal to 50% of the weight of the food fed? ... Of course not. ] Wherever it is, is it better for the fish that the waste is not visibly trapped in the matting? Do I want waste that does not settle out in the vortex chamber? Or, do I want solid stools that I can see and that do settle out in the vortex without breaking apart?

    I really do not know the answers. I have purposefully phrased my thoughts to create doubt about the usual "less visible waste means better digestibility" concept. That concept may be wrong, but the foods involved could still be the best for a different rationale.

    Anyone aware of published scientific studies on digestibility in fish and absorption of nutrient from different food sources?

  2. #2
    Oyagoi woodyaht's Avatar
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    I am right with your thoughts Mike!

    I have been feeding Hi-Silk for the first time and the waste is massive, but I am feeding them massivly as well, so of course the more you feed the more massive the waste load.

    I can't see how a food can produce less waste, per-say. Food goes in, food comes out. They don't have the ability to absorb to much as it goes straight through them.

    Maybe the food just breaks down quicker in the pond than other foods, and that appears to be less waste???????????????

  3. #3
    Nisai soelistyo's Avatar
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    i don't have scientific data or anything, but i've observed a very significant difference to water clarity between feeding Momotaro (for shiroji) and Saki Hikari growth.

    when feeding the momo food, water is very clear, but when feeding Saki Hikari, the water has a yellowish tinge and lots of floating debris.

    i thought it was a coincidence, but i've switched back and forth and it happens all the time. sometimes, it happens in a matter of one day straight after changing. I've heard from a few other friends that they notice the same thing too.

  4. #4
    Daihonmei dick benbow's Avatar
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    Just to throw a monkey wrench into the mix


    lots of living things as individuals do not digest things completely. they vary one to another.

    any human health nuts out there? Ever read the blood type book which graphically points out your strengths and weaknesses to disease, digestion, absorption according to your blood type? I gotta think koi are individuals too.

    When i feed Dainichi feed I notice the water turns a greenish tinge?

    Mike thanks for your thought provoking thread! I have no hard and fast answers
    only additional questions!

  5. #5
    Tosai
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    Mike,



    Part of your answer is the amount of ash contained in the food stuff. In this case one could define ash as all non digestible matter in the feed mix. Donít think this as a sign of a lower quality feed, but as an inherent quality of certain ingredients containing higher levels of ash.



    As of next week my newly built koi laboratory will be finished. It will be another 2-3 weeks until a full system test is completed before any stock would be added. The impetus for the lab is to conduct controlled experiments on koi growth and nutrition. Needless to say, Iím fascinated by this subject and if all goes well I should have plenty of material to discuss in the next 6-12 months concerning koi nutrition and diet.



    Mark

  6. #6
    Oyagoi woodyaht's Avatar
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    Quote Originally Posted by dick benbow
    Just to throw a monkey wrench into the mix


    lots of living things as individuals do not digest things completely. they vary one to another.

    any human health nuts out there? Ever read the blood type book which graphically points out your strengths and weaknesses to disease, digestion, absorption according to your blood type? I gotta think koi are individuals too.

    When i feed Dainichi feed I notice the water turns a greenish tinge?

    Mike thanks for your thought provoking thread! I have no hard and fast answers
    only additional questions!

    You made one hellofa point Dick! My ex-wife would only go to the bathroom about once a month, and that's the way their whole family was, they'd almost throw a party when they went. Hell she'd eat as much as me, and I'd always ask where do you put it, you aren't fat by any means!

    Questions like these will probably never have a definate answer.

  7. #7
    Jumbo koinut's Avatar
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    Quote Originally Posted by soelistyo
    i don't have scientific data or anything, but i've observed a very significant difference to water clarity between feeding Momotaro (for shiroji) and Saki Hikari growth.

    when feeding the momo food, water is very clear, but when feeding Saki Hikari, the water has a yellowish tinge and lots of floating debris.

    i thought it was a coincidence, but i've switched back and forth and it happens all the time. sometimes, it happens in a matter of one day straight after changing. I've heard from a few other friends that they notice the same thing too.
    Soelistyo,

    I was wondering which of the Saki Hikari you were feeding (growth, multi-season, color, or saki hikari basic diet) that gives your water a yellowish tinge?

  8. #8
    Oyagoi bekko's Avatar
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    Ash is part of it, but there is also digestible material which is not fully utilized. Its a multi-step process where food has to be broken down into simpler molecules and then metabolized. Digestion is technically the process of breaking down complex molecules into simple molecules. After digestion, the material must be metabolized. This is either through catabolism where simple molecules are turned into energy, or anabolism where simple molecules are recombined into complex molecules in the form of koi tissue (growth). It is possible to digest the food, but not metabolize it. This is just as wasteful as not digesting it at all.

    Where does it all go? The predominant elements in feed are carbon (C), hydrogen (H), oxygen (O) and nitrogen (N). What are the primary waste products? The predominant wastes are carbon dioxide (CO2) and ammonia (NH3) - carbon, hydrogen, oxygen and nitrogen. The fecal material is ash plus other feed components which made it through the gut without being digested and metabolized. Digestibility, in this context, refers to the ease with which the koi can digest AND metabolize the feed.

    That is about the extent of my understanding. I do not know why some feed components are easier to break down into simple molecules and metabolize. Temperature surely plays a role. Feed rate probably plays a role as well. The more a fish eats, the less efficient is the feed utilization.

    I raise a few seahorses, but am not very good at it. Seahorses only eat live food and seem to keep eating as long as something is available. Given an over-abundance of copepods or brine shrimp nauplii, the food passes through the gut so fast that the pods and brine shrimp are still alive when they come out the other end! Its seems like you have to minimize food availability in order to give the gut time to do its job.

    -steve hopkins

  9. #9
    Nisai
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    Hi.. Can I join the discussion?? I did some research on the koi digestive process and would like to share some of the things I learned. Actually, I started at the end of the process by examining koi feces and worked backwards through the fish to get a good grip on what happens in there. Some of this may be parochial but helpful in understanding it.

    1. The koi digestive system is incredibly simple and efficient. They do not have the acid-chamber (stomach) that mammals have to break food down and allow the gut to then absorb the essentials i.e., minerals, vitamins, nutrients, etc. Since koi are omnivorous (they eat anything), the gut is so designed to pass anything through it efficiently. The gut has bacteria and other chemical process that extract the essentials from what is passing through it and this is important when understanding koi health.

    2. Koi do not drink water. So all effective koi food must have moisture added to it. The added moisture is usually some exotic mix depending on the manufacturer (call them and ask them about their moisture mix) and is usually oil-based since we need to have the food resist breakdown in the water.

    For Mark, here is an experiment for your koi lab: collect a few samples of fresh feces using a commercial fish food (my preference is ShoKoi) and then desiccate the same food and feed it to the fish. You will need to hand feed them as the desiccated food wll break down quickly in the water. And then get some fresh feces samples and compare them to the first samples. The results are interesting. (I won't give them away just yet)

    3. Ash is added to the food as the most effective way to get minerals to the fish. Ash is just highly concentrated minerals after everything else has been burned off (literally). The gut processes look for minerals and extract them easily.

    4. The study of feces is fascinating (HONEST!!) and it can be a major indicator of the fish's health. When working with new koi owners, I like to tell them that what goes in is essentially what comes out. Most of us notice this when we switch commercial foods of different color. It is when we see white stringy mucous that we should be concerned as this indicates either a lack of gut bacteria (due to anti-biotics) or gut parasites causing an increase in gut mucous in an attempt to expel the beasts.

    5. The "digestive" process of koi is simple, as I mentioned. Whatever makes it in is ground up and passed into the gut so there are not many large chunks in the gut. This is about the only physical breakdown of the food and it is mechanical. The gut bacteria and chemical processes then extract what they need and the remaining reduced food is re-packaged for shipment to our filters. This packaging process involves the gut mucous to bind the particle together. It is this gut mucous that is the primary food for aeromonas bacteria as the day job for aeromonas is to start the waste breakdown process by eating the slime coat off of feces (and you thought your day job was bad!!).

    6. Koi do not get constipated. The chemical stimulation process that causes constipation when it fails is not a physiological process in koi. Koi do get mechanically clogged from time to time, but since the mouth-to-vent route is a straight shot (more or less), clogging is unusual. Remember they are bottom feeders and will pick and try to eat about anything.

    So, it is pretty clear that the physical composition of waste is not much different than the original commercial food going in and this is why the color going is usually the same color going out. When we see a change in water clarity and attribute it to feeding, it really has nothing to do with the digestive process but what the manufacturer used to "moisturize" his food or the added color to the food. And this leads me to my theory on why this particular manufacturer states that you will see less feces in your filter mat.. I contend that the reason is NOT because the food is more digestable but because he has found a way for it to physically break apart quicker so only the large feces samples are trapped by the filter while the smaller particles are in the water or processed in the filter (the reason for color change in the water??).

    Mother Nature has this figured out... if we left the feces on the bottom of the pond, it would all break down more or less... this is just the science of bacterial action. It is when food makers add things to the food that Mother Nature does not have a bacteria to breakdown that we see accumulations of left over food crud .. or when feces gets caught in rocks and other areas of anaerobic bacteria action that we have problems.

    Thanks for letting me join in..

    REC

  10. #10
    Sansai GazKoi's Avatar
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    Fascinating subject and one i have been looking into recently.

    I was feeding Dia Suki Gold and Hakari wheatgerm and that seemed OK then the Wheatgerm run out so i was just feeding the Dia Suki and the amount of waste has visibly gone up BIG TIME.

    I have contacted a few other keepers who have had very similar results with the same food,so are they not digesting it all,are they eating too much who knows but there is a difference.

    I am now just began to start mixing it with Momotaro so will keep my eye on it.
    Regards

    Gazza

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