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Thread: Overstocking

  1. #1
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    Default Overstocking

    Let’s talk about overstocking. To begin, the subject requires a usable definition. In the past, the traditional rule of thumb was 1 gallon/per inch of fish. This was obviously inadequate, but it was a reasonable generalization for most of the fish that were popular at the time. Still, even then there were some very obvious exceptions: goldfish and angelfish come to mind.

    Some people started giving the advice that 2 gallons/per inch of fish was more reasonable. Others argued, more realistically, that it depended not on the length of the fish, but on it’s mass (body weight). Unfortunately, for most people making that calculation is near impossible without removing the fish from the aquarium and weighing it. I am somewhat surprised that one of the breeders hasn’t come up with a chart specifically for discus, given they so frequently handle their fish. If it exists, I haven’t found it.

    Nevertheless, mass is the determining factor, everything else being equal. Therein lies the rub. No hobbyist’s aquarium is exactly the same as anyone else’s. Aside from volume (taking into account substrate, decorations, etc.) there is the issue of filtration. Some will say the number of fish is more important, but the number of fish in a given volume of water is rarely a limiting factor.

    I’ve mentioned elsewhere on this forum that I know a man who kept nearly one hundred fish in a 300 gallon tank, and none of those fish were as small as your common tetras. Most were 3 to 4 inches, some were larger. That implies he was providing less than one gallon/per inch of fish. And all of his fish were healthy and active. He accomplished this by using what he liked to call “over-filtration”.

    Commercial fish farmers who raise tilapia (a species of cichlid) for example, allocate less than 4 gallons of water per fish, each of which measure approximately 8” long (and weigh approximately 1 pound). That’s ˝ gallon/per inch of fish. Needless to say, they are simultaneously maximizing growth rate. It’s all about profit.

    This brings me to discus, specifically. The rule of thumb for discus keepers seems to be 10 gallons/per fish. Assuming the average discus is 6” long, that’s not very much different from the old “1 gallon/inch” rule, and it’s less than the “2 gallon/inch” rule.

    It seems unfortunate to me that most people seem to interpret the “10 gallon rule” as an optimal state for raising discus rather than the minimum for healthy, happy fish.

    I added the “happy” descriptor for a reason. It is absolutely possible to raise healthy discus using the “10-gallon/per fish” rule. Many people have been doing it for a very long time. In fact, I see no reason at all why one couldn’t raise healthy discus using only 5 gallons per fish, assuming proper filtration (and water changes). In fact, that’s pretty much what most retailers who display fish for sale do.

    Most hobbyist discus keepers would balk at doing this. That’s a good thing. But that doesn’t mean it can’t be done. The point I want to raise is this: Is 10 gallons per fish really enough for truly healthy, happy fish?

    Personally, I don’t think so. Not if you want “happy” fish. I’m not going to argue whether or not fish can feel happiness the same way we can. What I am going to do is define happiness as being able to express a full range of natural behavior within an environment that is conducive to it. I don’t think this can be done on the basis of 10 gallons per fish.

    What I am going to propose is simply this, volume per inch of fish isn’t in itself very important as far as physical health. What’s more important is how that volume is distributed. For example, I think the length of an aquarium is more important than either vertical or horizontal depth. I also think what I will call aquarium “flow” is important. What I mean by that is the way the volume is arranged, or channeled.

    My first aquarium (as an adult) was a 55 gallon tank. Initially, my interest was goldfish. Sometime later I visited an aquarium (tropical fish store) in Maryland, about an hour’s drive from where I lived. I do not recall the name of the place, but it was the largest fish store I’ve ever seen, before or since. As I recall, they stocked well over 200 tanks, with both salt and fresh water species. That was the first time I ever saw discus. I was smitten.

    I replaced my goldfish with four large juvenile discus. That aquarium was equipped with an undergravel filter powered by an air pump and decorated with black gravel and one moderately sized piece of driftwood, on the basis of the little I had read about discus to that point in time. As I’ve stated elsewhere, I performed a 30% water change once weekly. I never experienced any problems whatsoever. I never measured nitrates, or “conditioned” the water, which was straight from the tap.

    Two years later, I had to give up the aquarium in order to relocate to the opposite side of the country. Once settled in, I bought another 55 gallon aquarium. This time around I populated it, at one time or another, with a pair of Kribensis, a Jewel Cichlid, and several very small, very orange cichlids I have forgotten the names of and have since been unable to identify.

    I did not return to discus keeping at that time because I had already arrived at the opinion that keeping discus in anything less than a 125 gallon tank simply wasn’t optimal. And I had no room for anything that large.

    That opinion has not changed. Although I do think a 125 gallon tank is the minimum volume you should keep 6 adult discus in, it’s less about the volume than it is the 6 feet of length a 125 provides. I’m not saying a 75 or a 90 gallon tank isn’t suitable for 6 adult discus, only that at 4 feet of linear swimming space neither of those options is optimal.

    Let’s be clear here. Aquariums are prisons and their inhabitants are prisoners. The choice that the hobbyist must make is whether he wants to keep his prisoners in a bare cell, or something closer to “home confinement”.

    To take the analogy one step further, I will argue that keeping 6 adult discus in a bare bottom 75 gallon tank (much less a 55 gallon) is akin to maintaining a high security prison cell where everything that might cause injury, intentional or otherwise, has been removed. On the other end of the spectrum, 125 gallon tank properly decorated with substrate, driftwood, and plants is more like home confinement. The fish are going to be happier. I mentioned the importance of volume “flow” and this is where the decorations can contribute to, or detract from, the flow that’s possible with the 6 feet of linear space that a 125 provides.

    Now I’ve already provided what I think is a reasonable definition of fish happiness, but would like to take it a bit further. I have come across reports of controlled experiments demonstrating that fish (in this case guppies) do in fact display personality. I think it’s safe to say almost any cichlid keeper will confirm that.

    I’ve also come across reports of biologists using fish to observe the effects of medicines on depression and epilepsy. In the words of one biologist, “their (fish) nervous systems are surprisingly similar to humans”. I can verify from personal experience that fish can indeed suffer from epilepsy.

    The point being, fish do experience at least something similar to humans with respect to emotional well-being, if not genuine happiness.
    I understand the arguments against substrate and plants, but as far as I’m concerned those arguments are only really applicable to breeders and people keeping fish solely for their physical beauty. People who are also interested in fish behavior need to adopt a broader perspective.
    So, what is overstocking? From my perspective, there is only one clear-cut answer to that question. If your biofiltration system cannot keep ammonia and nitrite to near zero levels, you are overstocking (and/or overfeeding).

    You will notice I did not mention nitrate. Excessive nitrate is simply not an issue with any reasonable water change schedule. I’ve reported elsewhere that the Stendker discus folks intentionally raise their discus in water with 200 ppm nitrate.

    Piwowarski, another reknown discus breeder stated in an interview that he raises his discus in water with 25-150 ppm nitrate. Even his breeding tanks are kept as high as 50 ppm nitrate. He further states that his fish would do fine at even higher levels.

    There are numerous scientific studies of the effects of nitrate in commercial fish farming that also suggest even higher levels are safe for most fish, with fry being the most susceptible to negative effects.

    Enough said on that topic. Back to point.

    Some fish keepers do not keep discus because they find them “boring”. I suspect this is because they have observed overstocked tanks. You can see this yourself on any of the many Youtube videos displaying 15-20 discus in 125 gallon, or smaller, tanks. There is very little movement because there is nowhere for them to go.

    Keepers of African cichlids routinely overstock to reduce aggression. Even discus keepers routinely recommend “adding more fish” as a way to combat aggression. This is, in my opinion, according to my original definition, over stocking. It works only in the sense that it prevents the fish from expressing their natural behavior.

    On a related side note, I would like to mention a study done more than 10 years ago entitled, “Ecology and life history of an Amazon floodplain cichlid: the discus fish Symphysodon (Perciformes: Cichlidae)”. In it, the authors describe the differing social habits of discus during the low and high seasons of the Amazon Basin. The following is a quote from that study:

    During the rising water period, colonies in the galhadas of lago Amană disintegrated. Discus dispersed into adjacent flooded forests where they were thereafter observed alone or in small groups.

    The colonies, or galhadas, described above were said to consist of up to 30 fish. The colonies were believed to form as a method of deterring the increased number of predators during the low water season. The authors go on to say:

    During nightly observations in flooded forests during the high water period, discus were often seen alone or in groups of up to six, but never in larger groups.

    This may come as a surprise to people who think you should not keep fewer than 6 discus.

    On a final note, I only rarely see my discus forming a distinct school. They spend most of their time in groups of 2, 3 or 4 individuals and are often seen scavenging or simply resting alone. One of them prefers a shady spot underneath a large piece of driftwood, another prefers one end of the aquarium that is partially shielded by a separate piece of driftwood. Their positions and groupings change throughout the day.
    I believe this to be their normal behavior, given the space and proper “flow”. I would also like to point out that my discus seem to really enjoy probing small spaces in the driftwood and among the plants. During feeding time, they routinely pass up clearly observable food in open spaces to seek out bits in various nooks and crannies.

    I’ve also observed them squeezing themselves through openings barely large enough for passage, requiring them to rotate their bodies up to 90 degrees from the vertical in order to do so, for no apparent reason, other than seeing if they can.

    You simply will not see that behavior in a bare bottom, overstocked tank.

    My tank has a total volume of 685 liters (181 gallons). I estimate net volume at 600 liters (159 gallons). My occupants include 7 discus, 26 cardinal tetras, and 4 red lizard catfish. Adding one or two more discus without altering behavior is possible, but I consider my tank optimally stocked.

  2. #2
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    Default Re: Overstocking

    Some interesting points are made here for sure. Many of your points do indeed have merit. I would, however, like to respectfully differ on your comments/take regarding Nitrates.

    First, basing some of your reasoning on condoning high Nitrates with commercial fish farms is flawed in that those commercial fish are not raised for comfort of individual fish, but mere survival of fish prior to slaughter/use in the market.

    Secondly....and most importantly.... having healthy happy fish .....does.....(imho) include the keeper of fish to make the best attempt at completion of the Nitrogen Cycle (lower Nitrates). Understand that my jumping in here on this topic is partly due to the fact that I'm a retired biology teacher. I also maintain healthy discus fish, koi fish, and have been keeping fish for decades.

    For a fish keeper to work/strive to maintain proper/no NH3 (free Ammonia) levels and no NO2 (Nitrite) levels only to allow NO3 (Nitrate) levels to soar/be of no concern makes no biological sense. Having a cycle of any sort in a closed environment is most successful if it is allowed to be as close to completion as possible. My Nitrate levels are kept lower than 20 with heavy filtration (including denitrification facets), aeration, and WCs. The few rare times that I've accidently allowed the Nitrates to get higher (50-80), I've seen signs of lesser-than-ideal fish behavior. I guess I should provide an analogy to foster my points regarding Nitrates.

    1. Let's consider that Ammonia reduction would be like/compared to a factory producing a product.
    2. Let's consider that Nitrite reduction would be like/compared to a factory packaging a product.
    3. Let's consider that Nitrate reduction would be like/compared to a factory shipping out a product....... basically completing the commerce cycle for that factory......all is well.

    4. Now.......let's consider that no Nitrate reduction would be like/compared to a factory not being able to ship out a product. Such products would accumulate/build up to huge levels of stock not being able to shipped off creating a clogged factory warehouse with disastrous results and no successful completion of the commerce cycle.....all is not well. Just look at the results of a similar scenario going on with our ports.

    In nature, ideally, all cycles go through to completion for a healthy ecosystem. Why should our tanks be any different? For one to keep (after startup) NH3 levels at 0, NO2 levels at 0, only to have the NO3 levels go wild/be of no concern is not my understanding of a healthy tank, nor is it my practice.
    Last edited by 14Discus; 11-21-2021 at 11:55 AM.

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    Default Re: Overstocking

    Quote Originally Posted by 14Discus View Post
    First, basing some of your reasoning on condoning high Nitrates with commercial fish farms is flawed in that those commercial fish are not raised for comfort of individual fish, but mere survival of fish prior to slaughter/use in the market.

    Secondly....and most importantly.... having healthy happy fish .....does.....(imho) include the keeper of fish to make the best attempt at completion of the Nitrogen Cycle (lower Nitrates). Understand that my jumping in here on this topic is partly due to the fact that I'm a retired biology teacher. I also maintain healthy discus fish, koi fish, and have been keeping fish for decades.

    For a fish keeper to work/strive to maintain proper/no NH3 (free Ammonia) levels and no NO2 (Nitrite) levels only to allow NO3 (Nitrate) levels to soar/be of no concern makes no biological sense. Having a cycle of any sort in a closed environment is most successful if it is allowed to be as close to completion as possible. My Nitrate levels are kept lower than 20 with heavy filtration (including denitrification facets), aeration, and WCs. The few rare times that I've accidently allowed the Nitrates to get higher (50-80), I've seen signs of lesser-than-ideal fish behavior. I guess I should provide an analogy to foster my points regarding Nitrates.

    1. Let's consider that Ammonia reduction would be like/compared to a factory producing a product.
    2. Let's consider that Nitrite reduction would be like/compared to a factory packaging a product.
    3. Let's consider that Nitrate reduction would be like/compared to a factory shipping out a product....... basically completing the commerce cycle for that factory......all is well.

    4. Now.......let's consider that no Nitrate reduction would be like/compared to a factory not being able to ship out a product. Such products would accumulate/build up to huge levels of stock not being able to shipped off creating a clogged factory warehouse with disastrous results and no successful completion of the commerce cycle.....all is not well. Just look at the results of a similar scenario going on with our ports.
    Firstly, I did not "condone" high nitrate levels at commercial fish farms. I was merely using that to illustrate that a low nitrate is not necessary to achieving maximum growth rate, as is almost universally put forth as an argument for maintaining a low nitrate level.

    Secondly, "best attempt" to keep healthy fish is a non-starter. You either do or you do not maintain healthy, happy fish. You also ignored my definition of "happy" fish. It had nothing to do with nitrate level and everything to do with aquarium design and stocking which are absolutely the responsibility of the fish keeper. My argument is that those elements of fish keeping are far more important to keeping healthy, happy fish that trying to keep nitrate levels ridiculously low.

    Lastly, you fail to define "high nitrate level". You seem to imply that a level of 80 ppm is excessive and detrimental to the health of fish. Yet you completely ignore the fact that two separate, well-respected, successful discus farms raise their fish in water with nitrate levels between 100 and 200 ppm.

    I'm not arguing that's optimal for the long term health of fish. My point is, telling people they have to keep their fish in water with a nitrate level below 20 ppm is simply spreading misinformation. I personally try to keep nitrate levels below 80 ppm. In fact, I've never seen them go higher than 50 ppm. I only make a 50% water change ONCE EVERY TWO WEEKS and have no problem keeping nitrate below 40 ppm. I've gone as long as 3 weeks without a water change, and I'm almost certain I could go a month and never see a nitrate level even approach the level of those discus farms I've referenced above.

    Given those facts, anyone who is experiencing an excessively high nitrate level, let's take that to mean over 80 ppm, well, they have a problem with overstocking and overfeeding. It's as simple as that.

  4. #4
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    Default Re: Overstocking

    D'Bunk, many points/thoughts in your initial post are things I can agree with, but also feel a few things are screwed (e.g., using different fish to compare to discus... even other cichlids like mbuna to discus are apples to oranges depending on the angle). I DO love certain points of how you discuss that discus can routinely be found in groups of 6 or less in nature... but I know they'll school together in nature to move greater distances as a group for protection in numbers (therefore we hardly see them school in our tanks... which I totally agree a small group in enough space is SOOO much more interesting to me than a large group... but, IMO, not accurate to discount that they don't school).

    So much more I want to write (I love the debates & stances) but lacking time right now. However, I'm strongly with Bill regarding nitrates stance. I DO believe that some folks have some dang awesome element that somehow allows their discus to grow crazy big even with high nitrate levels... but longterm health may be separate from "big" and "happy". Hell, I'm an idiot who's smoked for too long and could slow down on drinks on the weekends, but I'll be damned if someone said I wasn't happy However, I have a choice on my lifestyle (unlike the fish). Pretty much, I wonder (like me as an example human) if even great growth and happy fish are faced with a shortened lifespan due to the lifestyle we've chosen for them (although great growth and happy... my question is how long will they be fertile, how long are their lifespans, etc... I cannot know unless I witness it or witness well documented cases over time). I definitely love the discussions but I wouldn't be too quick to discard Bill's points, just like how I have no creditable info to go against anything you said (although my collection of hard lessons learned definitely influence me).

    Have to cut myself off due to work stuff but hoping none of what I said here gets you steamed up, boss... I love the different view points & thoughts but also trying to figure out how to keep the "Mizzou challenge" before readily agreeing.
    -Elliot

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    Registered Member bluelagoon's Avatar
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    Default Re: Overstocking

    I found this on Piwowarski Discus. The only thing I couldn't find out was the amounts of antibiotics used in housing large quantities of fish kept together, which I'm sure they all do. The flagellates that were mentioned, I guess that would be the protozoa hexamita and is also non as a parasite. Another thing in the second paragraph states an 80% WC gets better growth, I wonder why he put that in his write out? I do know from experience (over 50 years of keeping fish) the more and frequent WC's keeps disease at bay. Nitrates is something that I've never measured in all those years. But years ago I did have a few tanks crash from not changing enough water, which I learned here on SD about 20 years ago of the importance of maintaining a clean and frequent WC's in such a small environment that we keep the fish in; after all it is not the Amazon River where WC's are continuous. This past 50 years things I've read on nitrates and fish is high nitrates is not a good thing, Altho some folks have high nitrates in the tap water. Knowing this why would anyone want to let the nitrates get high and put the fish in harms way. When nitrates get high some of the compounds in the water gets depleted and metabolized and gets concentrated with nasties and that flagellate mentioned can take off because of the weakened immunes system that was created by dirty water. https://diskuszucht-piwowarski-shop.de/FAQ

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