Understanding Koi Aquaculture

The word aquaculture itself is defined by Webster’s as “the cultivation of aquatic organisms”. However, in my opinion this word can be more literally and accurately defined. Let’s break the word itself down into the two words; “aqua” and “culture” or water and culture. Now put them back together again and they literally mean “water culture”.  So to me the word “aquaculture” would be better defined as ” the cultivation of water  for the purpose of raising aquatic organisms”.

Now aquatic organisms covers a broad spectrum of plants and animals, from plankton, algae, oysters, shrimp, etc., all the way up the chain to types of fish. Each aquatic organism has their own very specific needs and requirements when speaking of the chemistry of the water they live within.  For the purpose of this writing we will solely be focusing on fish, and, more specifically, Koi as that specific aquatic organism.

The point of all of this is to relay to you that it is the water that is the key to the success or failure of raising any aquatic life form. Learn all you can about taking proper care of the water as it relates to Koi specifically, and the Koi will most likely take care of themselves and thrive. I cannot stress this fact enough. The health of the water as it relates to Koi specifically is the key factor to their health, longevity, and well being!

Firstly know and understand that Koi, or any fish for that matter, require certain basic things to survive, and more importantly to thrive in any given body of water. Please note, however, that there is a major difference between these two words: survive and thrive! Some information out there (not specifically differentiating between these words), may lead you to some misconceptions and even misinformation in your fish keeping research. Even amongst certain aquaculture professionals, some of this incorrect or misapplied information is still believed to be scientific fact relating to Koi.  In some cases this is simply not the case. In all of this, raising Koi in a backyard pond or tank is absolutely considered a form of aquaculture. Even raising a few fish in an aquarium is considered a form of aquaculture. Having a fish simply survive is a far cry from having it thrive and live a long and healthy life to its fullest potential.

Fish have some other minimum basic requirements as well to be able to thrive in any given body of water. Things like oxygen content, pH, alkalinity/kH,  general hardness, temperature, carbon dioxide, and the influence of other chemical compounds like heavy metals and such – these are just some of the primary parameters to be concerned with. Some of these are required at particular levels in the system, and some are not desirable and even harmful at any level. Even our polluted rainwater can negatively influence many species of fish, especially in our small, closed, artificial outdoor systems. Also, many of these listed compounds can have influences between each other. These chemical interactions can at times be harmful to the fish because they usually cause one thing to change the chemical properties of another within the water chemistry. In other words, one compound by itself can be harmless or even a good thing, but when influenced or combined with another, may end up deadly.

So as you can begin to understand, the water plays the most significant role in fish health and prosperity.  Understanding this, as well as how to properly manipulate it, is the heart and soul of aquaculture. In future chapters I will spend a great deal of time and go into much detail on this subject matter. If you get anything from this chapter, make sure you fully understand this very important part of fish husbandry.

The Hobbyist VS. the Professional

You must understand that fish aquaculture has many levels, and varied purposes. For example, there are fish raised to end up on someone’s dinner table, and this is generally known as food fish culture. These include species like striped bass, catfish, tilapia, and many others, both freshwater and salt water species. Then there are fish that are raised for the primary purpose of being pets, that are generally known as ornamental fish. These two categories or types of fish have very different, specific needs and requirements. As well within these categories, there are hobbyists, and there are professionals. While most of the general and basic science relates to both categories and subcategories within, how and why the science is applied is where things can vary. This is where many people can get confused in researching how to properly care for Koi.

Generally speaking, in most, if not all cases, food fish are raised by professionals as a business. However, there are some people that raise their own food fish as a hobby, for their own consumption. On the professional level, these fish are raised in such a way as economics plays a major role in how it is done. Economics in many cases does not always coincide with the word thrive, however. In this case the primary goal is strictly keeping the fish alive until it’s time for them to be processed and/or go to market as food. As well, in most cases due to the economics of things, fish are purposefully crowded to achieve the most efficient means in growing and harvesting them. This is the definition of economics after all.  Of course they still must somewhat thrive, but only to a degree to obtain the maximum growth required to make a profit in a given short time frame. In other words, these fish are generally only raised for the short term in most cases. Either professionally or otherwise, this endeavor in growing many fish in a somewhat small area or system is known as intensive aquaculture , and it is primarily economically driven.

Now the hobbyist and even the professional dealing with ornamental fish as opposed to food fish species need the fish to thrive for the long term. The primary objective here is to have the fish live long and healthy lives. However, there is still a major difference between the professional and the hobbyist within this ornamental fish culture. With the ornamental fish professional, economics still plays a major role with making a profit as a business, and this is also considered a form of intensive aquaculture. On the other hand, the hobbyist of ornamental fish culture has only one objective. This is to have the fish fully thrive to the point that they live their entire possible life span as pets. This in most cases will not fit the description of intensive aquaculture, because in most cases the stocking densities are far less than that of the professional. As well, there are no true economic factors other than that individual’s budget in designing and building the best possible system to accomplish this within their personal monetary means.

On the professional level, however, in raising literally tens of thousands or even millions of ornamental fish yearly, we are always “pushing the envelope” so to speak. Due to the economic factors, we need to grow and sell as many fish as possible within a given space, to be able to make a profit as a business as well as meet the demands of our customers in offering many varieties. As well, there are other factors that are involved on the professional level. Genetic manipulation, for example, is one of them.

As a professional in the ornamental industry, my goal is all the above, but as well to create a genetically superior Koi. In doing so I want to weed out any genetically inferior fish as well. These are fish that are weak, runts, deformed, low quality etc. So with this in mind, you must understand that we have purposeful and accepted losses. Remember this, as it is critical in your understanding of  how and why things are done differently from the professional level to the hobbyist level. Understanding these differences will minimize the confusion in researching proper Koi husbandry.

For example, in the Koi industry culling is a very important factor in creating genetically superior Koi, as well as the best quality Koi in terms of what makes a good specimen in a given breed or variety. Culling is  nothing more than picking out genetically inferior fish that do not meet the aforementioned criteria and removing them from the gene pool.

This is a very critical factor in being a successful Koi breeder and in more ways than one. You see, Koi can lay up to a half a million eggs, and in nature most of them would be eaten before they even hatched! Even the parents eat the eggs as they are being laid! On top of this, more would fall prey to other creatures even if they did make it past the hatching stage. Even certain aquatic insects prey on the eggs and the hatchlings! All of this is how mother nature culls out the weak, inferior, and excess specimens. It’s all part of what is referred to as “natural selection”.

With the artificial cultivation of Koi as a professional breeder, you must understand that we do things in such a way as most of them hatch and survive. As you can imagine, this would end up being far too many fish to economically and feasibly raise even on the professional level.  Not to mention, this would be far too many of a given variety as well. So these are just a few reasons that we must cull out inferior specimens. This as well helps assure that you, the customer, gets only the best fish, both genetically speaking in terms of quality and in terms of physiology.

So as you can see by now, there are major differences between intensive aquaculture on the professional leveland the hobbyists. However, even certain hobbyists can have goals as such that they too could fall into the realm of intensive aquaculture. How many fish raised in a given space is what dictates this fact for the most part.

Let me emphasize now, that the fewer fish you house in a given body of water, the fewer health and water quality issues you will experience overall.

Does the above statement mean that there is no place for intensive aquaculture in the hobbyist world of Koi? Absolutely not! It simply means that if your desire, and your goal is to house as many fish as possible in a given body of water for whatever reason, then you will be required to take the intensive aquaculture approach with your husbandry skills and research. So it is critical to figure out what your goals are and, as such, design things around them.


 Stocking Densities

I get asked all the time, “How many Koi can I have in my pond?” Well, as with most things in aquaculture, there is no one answer for this, as it is a very relative, as well as subjective question. Relative to many, many variables, and subjective as to whom you ask. The answer totally depends on your goals as a hobbyist.  As well, it depends on things like your knowledge base of Koi and water husbandry skills, your budget,  the equipment utilized for filtration (if any), your upkeep and maintenance practices, space limitations, and many other such variables.  So as you can begin to understand, the answer to the question of stocking rates in a given system has many variables associated with it. However, at the end of this section I will attempt to give you some very basic and very generalized rules of thumb of stocking densities. It is critical, however, that you have read through the text preceding my opinion on this.

As an example to some of the variables previously mentioned: let’s say a person has a 1000 gallon pond with no filtration, and does not test and maintain their water. They know nothing of water quality, and therefore do not test their water.  Firstly this person should not have many Koi, if any. While it is still possible in this scenario to put Koi in there, they would not grow much, or thrive, and most likely be under constant stress, and die at an early age. You must understand that Koi can live for 40 to 60 years!

Now a person with some sort of mechanical, and/or biological filtration, a basic knowledge of water quality, and who also tests and maintains their water can safely have a far greater number of fish than the aforementioned person. As well, these fish can thrive, grow and live long lives. So once again we are back to those words, thrive or survive. However, your goals as a Koi keeper will also dictate how many fish should be kept within a given system and design.

For example, if you want your Koi to grow to their largest size capable genetically, (and this can be as large as 40″ or more) then this consideration will severely limit the number of fish that should be stocked as well. You have to understand that to obtain optimum growth, you must feed them high protein food of good quality and lots of it! This in turn will speed up the downward spiral to poor water quality if your system is not designed for these high protein feed rates. You must also realize that even if you first purchase smaller fish at say 4″ or so, these fish are capable to grow to that 40″ mark! So if you put the maximum number possible of these smaller 4″ fish in the system, to the point that it then maxes out that system from a water quality standpoint, you have left no room for growth. They will still grow, but minimally, and never be able to reach their maximum potential. Even with minimal growth, the system was already maxed out with them being only 4″. So as they grow they will outgrow the system quickly, and this could lead to a total loss of the entire population at some point due to water quality issues.

So as you can see, it is critical when speaking of stocking density to allow for the maximum growth of the fish in this scenario and considering the primary goal of optimum growth. The only solution here would be to improve and increase the size of your system and filtration as needed to accommodate this growth over time, or to lower the total number of fish you were to start with in the first place. So in this scenario, with optimal growth in mind, this person could have “X” number of fish limited by the previous facts.

Now if we were to take another person whose goal was primarily to have many fish, and this person was not concerned with their growth rates, this is yet another scenario that requires a different approach. They too must still maintain proper water quality, and they too would still have to be concerned with future growth that will still most likely occur. However, these fish should be fed minimally. Minimally meaning enough as to keep them healthy and thriving, as opposed to feeding the maximum to achieve fast and large growth. In this case, however, the person in this scenario would have to increase the size and function of their system as well over time, but there may be a greater time period before this is required as compared to the first example. Remember, these fish will not grow as much as the previous example, due to what we have discussed so far. So in this scenario, this person could have “Y” number of fish, and more than the previous example possibly.

The Professional

To help you better understand this complex issue of stocking density, I would like to discuss one other scenario. This would be the professional Koi keeper such as myself, or anyone that sells Koi for a living. We previously touched on this, but now I would like to go into a little more detail from another perspective.

As a professional, my goal is to give you the customer the best possible selection of fish to choose from, as well as the healthiest. Remember, however, that space and economics now come into place as compared to you the hobbyist. So in my case I want to safely and feasibly house as many fish as possible in a given space. There is one very important factor within this that allows me to do this. So please understand the differences that I am about to discuss.

The number one factor that allows me to have extreme stocking densities is the simple fact that my fish are only housed in my systems for short periods of time. They are not spending their entire lives in my retail systems, as they get sold quickly. It is critical that you understand this fact. With this in mind, I must have a complete and total understanding of water quality, the best design feasible, and exaggerated filtration. All of this combined is what allows me to accomplish this.

However, remember this statement from previous text ?

Let me emphasize now, that the fewer fish you house in a given body of water, the fewer health and water quality issues you will experience overall.

 You can also say this in reverse to better apply to my case:

The more fish you house in a given body of water, the greater number of health and water quality issues you will experience overall.

While with my knowledge and understanding of water quality and how to maintain it there still will be health issues, and even water quality issues at times. The question here is to what degree. Most water quality issues are very temporary, as in my operation the water is monitored and corrected on a daily basis. Therefore losses or health issues due to water quality directly almost never occur from this fact alone. As well, growth rates while in the retail systems is not a consideration. We achieve those in the mud ponds, prior to them ever making it to the retail systems or quarantine tanks. As well, you the customer and end user will continue this growth process once the fish leave the farm. So for this reason, the fish in the quarantine and retail systems are fed minimally as to keep them healthy and stress free from a nutritional standpoint. As well, they are not fed too much as to have the water quality be on edge all of the time.

Now as far as general health issues not concerned with water quality or feed rates, it is a given that these can and will occur even on the professional level. You see, when you crowd fish to the degree that we do on a professional level, the sheer number of fish being in so close with one another is a factor that can only be contended with to a degree. Here is yet another place that accepted losses or issues will come into play. Yes, even here we will have occasional health issues with fish in the retail tanks. However, we constantly monitor the fish for such problems.

Depending on the size of fish in question, I can have as many as one fish for every half gallon of water in a given retail system! (Oh how I can imagine some of the more advanced hobbyist reading this are cringing right about now). Open your mind and hear me out.

As you might imagine, these are extreme stocking densities to say the least! With this fact you must understand that the fish can be literally shoulder to shoulder in there at times. This in turn can cause them to constantly be in physical contact with each other. Due to this crowding you end up with some fish experiencing broken fins, scale losses, and even cannibalism! All of this is especially true during feeding time. Quite often feeding is not done on a daily basis depending on many factors. With this fact, you can imagine when we do feed them that all these fish quickly and aggressively come to the surface to get their share of feed.  Many times this is where physical damage to one another can and does occur.

As well, there may be some fish in there that are simply not aggressive enough to get their fair share. These fish will end up becoming  weak and possibly even emaciated to a degree. So at some point in our observing and inspecting the fish during feeding time, any fish with issues will be removed from the system. These fish were fine when we put them in the system, but over time within the system these things can occur. This is simply a fact of life with intensive aquaculture. Occasionally if they are young fish, we will simply remove them from the system and put them in a less crowded one, or back into the mud ponds to grow more if emaciation was an issue. Hopefully they will grow out of their shyness and also to the point that they can compete with the others during feeding times. This is yet another way in which we help assure that you get only the strongest and healthiest fish possible.

One other aspect of crowding fish are pathogens like harmful bacteria and parasites.  Let’s just call them “bugs” for short. You see, even fish that have been fully treated still house a debatable percentage of these bugs on and within their bodies. I use the word debatable because I am currently on the brink of discovering just how many bugs our standard treatments miss, as well as just how many they can contend with and not acquire health issues. My current thoughts on this are that we only actually kill a small percentage of bugs as compared to what current science believes we do, and that many more remain unharmed, and yet the fish still survive and thrive. However, this small percentage we do kill with treatments seem to be enough to keep the fish safe and healthy. So to date it seems that fish can survive and even thrive with a far greater number of resident pathogens than once thought. (We will discuss this fact amongst other related facts in detail in future chapters.) So in understanding this, it is easy to see that in a crowded tank, the bugs can easily and quickly propagate at times, grow to unmanageable numbers, and attack and harm the fish.

As stated, fish ALWAYS house some form and number of bugs on and within their bodies. They live and coexist with them all the time and without issue. However, any form of stress can cause some fish to be overcome by these invaders. There are various reasons for this. One reason could be that just as with humans, some fish are simply more genetically susceptible to get sick easily. They have a weakened immune response.  Again, these are considered weak and inferior fish, and again we would want them culled from the genetic line. Many times these fish on the farm are discovered in the quarantine stage and are removed before they ever get to the retail tanks.

Overcrowding fish itself is a form of stress, and with this fact, know that a stressed fish is more prone to get health issues in general. My goal as a professional is to keep these issues to a minimum, and I do so with knowledge and experience. No one, and I mean no one, can totally eliminate possible health issue 100%. This is especially true on the professional level and with intensive aquaculture. Anyone who says they can has little experience overall and simply does not know what they may think they know about Koi.

So as you can begin to understand, there are some basic considerations for keeping a given number of Koi in a given size system. The primary things required are filtration (preferably biological and mechanical), space for the appropriate volume of water, maintenance of that water and system, and most importantly a good basic understanding of what good water quality is and how to achieve it. Putting this all together and having the properly designed system to achieve these things is the basic requirement for even being able to have Koi safely and feasibly!

So to finally answer the question originally posted, I will give you my opinion and some very basic guidelines as to how many fish you can safely have.

All of what I am about to give you is based on the assumption that you have some form of filtration, at least 300 gallons of water in the system, a basic understanding of water quality is and how to achieve it, and most importantly that you test and monitor the water on a regular basis. This does not include aquariums, as they need to be addressed separately, and my answers would vary from below. This is yet another very different world of Koi keeping, and thus needs to be addressed as such at some other point.

It is also critical to understand your experience level within the hobby plays a major role in stocking density, as this is also how I broke down my stocking density numbers. Are you a beginner, an intermediate, or an advanced hobbyist?  Experience in years in raising Koi means little, whereas experience in years combined with handling many fish over those years gives you a far greater experience level. In other words, you could have a person that has raised a handful of Koi, somewhat successfully, over a thirty year time frame. Is this an advanced hobbyist? Well to some degree yes, but to a larger degree no. It totally depends on whom you compare them to. Comparing them to an absolute beginner just getting into the hobby, then yes, they are advanced as compared to that beginner. However, you must understand, that even though they have had Koi for thirty years, their experience level is based solely on only that handful of fish. So again let me pose the question, is this an advanced hobbyist? The only reason I mention any of this is to help you keep an open mind as it relates to learning new things, as well as help you decide where you fall in experience level.

I leave you with this:

Experience as it relates to time is one thing, but experience as it relates to time as well as numbers of fish/experience is another.

 So….. How many fish can you have?

For the absolute beginner hobbyist I would recommend no more than one fish max per one hundred gallons of water. This depends on your goals of course. Once you become proficient at water testing, you may eventually advance to the next level and possibly more fish. This advancement can happen as quickly as one season.

For the intermediate Koi keeper that is already proficient at testing the water and has a complete understanding of the same, as well as has the design and equipment to properly maintain all of this, then I would say you could have as many as one fish per fifty gallons of water.

For the advanced hobbyist, and for some  beginning level professionals, I would say you could safely have one fish per twenty five gallons of water. Again, this is considering your personal goals. However, it is likely that if you are truly in the advanced category of Koi husbandry skills, you will most likely be heading in the opposite direction, and housing less fish overall unless you are doing it professionally. The reason for this will become obvious with the increase in your experience and knowledge, and possibly as you read on through this book .

Nature’s Way?

I see many references in comparing our artificial closed systems to mother nature’s natural, open environment. Well let me tell you with utmost confidence, that generally speaking of the average or even the advanced  hobbyist, there is simply and absolutely no comparison to Mother Nature. This is with respect to size of the system, as well as stocking densities specifically, as well as a few other factors.

I don’t care if you have a million gallon pond with only one Koi in it, that in no way can be compared to what Mother Nature would allow or supply. Understand that nature does things from a biological standpoint primarily. We on the other hand do things from a biological standpoint as well, but when speaking of raising fish, we add in mechanical aspects also. We also attempt to interject human traits and desires into things. With this fact alone we are going against nature’s way of doing things. Mother Nature does not have feelings! In general, nature has  no consideration for the longevity of a species, or at least this consideration is there to only a  small degree. Many species within nature have definitive life spans on this planet. There are peaks and valleys within their existence as well. In other words, as a species begins to evolve, it must adapt to the ever-changing world around it. The degree to which it does this dictates the longevity of the species. That given species will adopt or go extinct based on the other factors and conditions involved within nature.  So as previously stated, within the given time frame of that specie’s existence, these factors will cause peaks and valleys in their population and overall place within nature. This fact greatly differs from our goals as humans. We of course want every species to survive and thrive, and this does not always coincide with Mother Nature’s plans or outcomes.

Another example of the difference between how we do things as compared to nature would be the body of water itself. We as humans want our systems to be crystal clear. Let’s face it, seeing the fish is a big part of enjoying them! Well in many cases within nature, a natural body of water is not clear. There are exceptions, of course, but in general a clear body of water in nature is an almost sterile one many times, not containing much in the way of aquatic life. This is especially true when referring to low flow freshwater environments with little to no new water influx . You have to understand as well, that a given body of water within the natural world also has a definitive life span. It too will experience peaks and valleys in terms of its ability to support aquatic life forms. Understanding this, you must realize that the “clear” stage of that body of waters existence is usually not the stage that supports the most aquatic life. Things like algae, plankton, and other types of things that make the water turbid are usually the beginning of the food chain in that body of water and therefore critical in its further development. With this beginning, many aquatic life forms will evolve and later better support a given fish species.

So with this in mind, you may as well get it into your head, that we are talking about two very different things here when speaking of comparing our systems to mother nature! It simply is not feasible or logical to think in these terms. All we can do is learn the science from nature and attempt to apply it to our specific and artificial situations and variables.

You must also understand as well, that with all the varied goals and other factors involved between each class of aquaculturist, that there is simply “more than one way to skin this cat” so to speak. Understanding the variables, or more exactly the differences in variables, from one person to the next, is the critical element is deciding what is best for a given situation.

For example, you can practice what I refer to as “bubble boy” Koi keeping. This is when you have very minimal stocking densities combined with the best equipment available to maintain proper water quality. In addition you would have the largest system of water possible, as well as the time to do all the maintenance and husbandry practices needed to achieve the healthiest fish possible. Does all of this assure that there will never be health issues….of course not, but it will go the furthest in attempting to obtain that goal. In general, this type of hobbyist is in the advanced stages of Koi keeping, and usually have very expensive fish, and very large budgets associated with their hobby. Many times these same people are the ones that show their fish as well. Some of these types of fish can cost thousands, and even hundreds of thousands of dollars each! So as you can imagine, these types of fish are pampered to say the least. As well, the size to which these fish are grown is also a major consideration, as very large fish are desired amongst show enthusiasts. For this reason alone, a low stocking density is mandatory to achieve the highest potential growth rates.

However, not all people can, want, or need to do this for a multitude of reasons. These are the average folks out there that have anything from a watergarden to a true Koi pond, solely designed for the purpose of raising some fish as pets, and for the enjoyment and aesthetics of the water feature as well. So as you can see, it is critical to first identify your goals in the world of aquaculture and Koi. Learn the basic science of water, then modify what is needed to accomplish this.

Written by John N Fornaro. All Rights reserved. Hanover Koi Farms LLC. Copyright 2017

Back to Top
Previous Page