Monday, April 25, 2011

Aggression of Koi Experiment

The experiment that is being performed is designed to test whether or not koi will show aggressive behavior towards other types of common pond fish. The hypothesis is that koi will display aggressive behavior towards fancy goldfish. The types of pond fish that are being used are fancy goldfish called fantails, calicos, and blue oranda. The main reason this experiment is being preformed is to see if koi and fancy goldfish can be kept together in the same pond without having the different types of pond fish fighting. Koi mainly live in private ponds although some can be found in streams. Carp in Japan were grown in rice fields so that the farmers had a good source of protein during the winter. Over time the farms noticed that some of the crap started to get spots of color on them. Carp are originally a brown to black color. So the farmers caught the koi that had the color spots on them and being to selectively breed them. Then this process was repeated over several generations of crap until vibrate color patterns were achieved, these carp were then given the name koi. (KOI HISTORY)  It is the beautiful color patterns that the koi posses that make them attractive to people so that they will buy them as pets. The diet of koi consists mainly of high protein based fish food in the summer mouths and in the late fall to early winter they eat low protein fish food pellets or they don’t eat at all. The reason koi do not eat food or eat low protein food in the winter is because their metabolism slows down significantly compared to their metabolism in the summer. Low protein food is given to koi in the winter because they are not able to digest protein as well as in the summer months. Koi can grow more than twenty inches in length and can live for many years. Some of the brood koi that are currently being used at Mt. Parnell’s Fish hatchery are between thirteen to sixteen years old. However some koi can potentially live to reach 100 years old but they require very specific environment to reach that age.The water that they live in must be maintained at a temperature around thirty five degrees Fahrenheit and the pH of the water must be kept at 7 or very close to 7. Along with the temperature and pH requirement the pond water that they live in must be filter so that the fecal material is constantly being removed from the water.       ( Raafat ) This is important because the fecal matter that they excrete contains concentrated amounts of ammonium, which can be very harmful to a koi if the amount of it in the water is not regulated regularly.
                The area in which this experiment was conducted in was in a fifty gallon glass fish tank. The koi and the fancy gold fish that were used in the experiment were donated by Mt. Parnell’s Fish Hatchery. The koi that were used in the experiment were three to four inches long and were about two years old. The koi that were used were yellow, standard fin, koi. The fancy fish were about five years old and were five to six inches in length. The glass tank was set up on a wooden stand inside a house that was kept at a constant temperature (sixty five degrees Fahrenheit). Large (about the size of your palm), smooth pond rock were added to the bottom of the tank to simulate the bottom of the pond that the koi came from. Then water from a well was added to the tank and was filtered by a charcoal filter for two days before fish were added to the tank. The water in the tank was kept at room temperature (sixty five degrees Fahrenheit) and at a pH of 7 ± .2 at all times. One charcoal filter was placed along the side of the tank so that the bottom half of the filter was in the water to filter out waste material produced by the fish.  The tank was aerated by one aerator that was connected to an air stone that was placed in to the tank so that the waters’ oxygen levels remained constant. Then two plexly glass that were cut to be one centimeter shorter then the width of the tank but just as tall as the height of the tank were placed into the tank causing there to be three sections inside the tank (The reason that the plexy glass was cut shorter than the width of the tank was to allow the aerated water to circulate evenly throughout the tank).While the tanks were being set up the koi and the fancy goldfish were kept in a separate concrete pools at Mt. Parnell’s Fish Hatchery. Once the tanks were set up one koi and one fancy fish were placed into each section of the tank.  The fish were then observed for twenty minutes and aggressive behavior was quantified on a piece of paper.  Once the experiment was performed the koi were removed from the section of tank they were in and the fancy goldfish were left in their respective sections. The fancy goldfish were given one hour to be alone in their section of the tank so that they could recover before new koi were placed into the section with them. This experiment was performed ten times with one control group. The control was set up the same as the above experiment but instead of adding a fancy goldfish to the tank another koi was added with a koi in one section of the tank.
                The data collected from this experiment was categorized into three types of aggressive behaviors. The aggressive behaviors included biting (B), chasing (S), and mock biting (C). Mock biting was when a koi would go up to the fancy gold fish and start to bite close to the fancy goldfish but without actually biting it. The most prevalent aggressive behavior the koi performed was chasing the fancy fish. The aggressive behavior that koi did the least amount was mock biting. In the ten experiment that were preformed (including the control) the biting behavior was observed a total of 114 times, the mock biting behavior was observed 78 times, and the chasing behavior was observed a total of 252 times.  Figure can be seen in the link below.

Figure Caption:  The above figure shows the aggression of koi towards another koi. The data in the above graph is data that was collected from one control experiment. The B stands for the biting behavior, S stands for the chasing behavior, and the C stands for the mock biting behavior. Looking at the figure it can be seen that the most common aggressive behavior observed was chasing and the least common behavior observed was the biting behavior.

Figure Caption: The above figure shows the aggression of koi towards fancy goldfish. This data includes data from nine experiments The B stands for the biting behavior, S stands for the chasing behavior, and the C stands for the mock biting behavior. Looking at the figure above it can be seen that the most common aggressive behavior observed was chasing and the least common observed

                After the results of the experiment had been analyzed it is clear that koi and fancy goldfish cannot coexistent together in a pond. The koi showed a high tendency to bite the fancy goldfish. This sometimes resulted in the fancy goldfish receiving tears in their fish which would make them more prone to getting diseases.  Another interesting observation that was seen while performing the experiment was that both the koi and fancy goldfish seemed agitated being placed together in one section of the tank, but when two koi were placed in one section of the tank they seemed to get along relatively well.  Other interesting side observations were made during the experiment when the koi and the fancy goldfish were placed into one section of the tank; the koi seemed to set up a territory in the section of the tank. When the fancy goldfish entered the territory of the koi, the koi would then act aggressively towards the fancy fish. When compared to the koi that were kept together in the holding tank, the koi all seemed to cluster together and no defined territory was set up by any one koi. The results of this experiment will help future and current pond owners better understand the temperament (aggressiveness) of the koi that they own. So that they can make better decisions as to what types of pond fish they can add to their pond that contains koi. Some aspects of this experiment could have been improved. The number of experiments that were preformed should be increased so that the data is accurate. The experiment should be conducted for longer periods of time, different times of the day, and with different environmental setting to ensure that the data is accurate. Another thing that could be done to help improve the results of the experiment is to set up three ponds with the same environmental conditions. In one pond put both koi and fancy goldfish into the pond. Then in the other two ponds place strictly fancy goldfish into the one pond and strictly koi into the other pond.  Then allow them to live in their respective ponds for an extended period of time (many years). Then as the fish in the ponds die record the number of fish that died in a day, the date when it died, and what pond it died in. Then after many years has passed look at the death rate for each pond.   Then compare the data that was obtained from that experiment and compare it to this experiment to see if there was a correlation. If there was that would strengthen the hypothesis: Koi will display aggressive behavior toward fancy goldfish.
Works Cited
KOI HISTORY. 24 Apr. 2011 <>.
Raafat, Nadia and Margaret Pembridge. Fury after Freddie’s koi carp worth £1million die. 24 Apr. 2011                 <>.


  1. This is a really good read for me, Must admit that you are one of the best bloggers I ever saw.Thanks for posting this informative article.
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  2. I tried placing together ranchu fancy goldfish and panda moor goldfish to our koi pond and the kois eat the eyes of the poor goldfishes. That's why I really agree on this experiment base on my experience.

  3. Well this fancy goldfish is fucked because the only other tank I have available has a gator in it...

  4. My kois are aggressive
    They always hiding
    Pls help me

  5. My kois are aggressive
    They always hiding
    Pls help me

  6. I had a Subunkin in with my Husbands Koi and they ate it, I had to remove my goldfish out of his tank and put them in a smaller tank because of the endless biting and killin gof my goldfish, All but two of my goldfish are gone... koi still here, so in the long run, never out them together.

  7. I had koi and Oranda god fish in my 3200 gallon pond for years and they koexisted just fine together. My older koi ranges from 18'' to 35'' and i had 7 orandas wih them together. Everything was peaceful til last year I added a few new 5-6'' koi. The new small koi started to attack my orandas: biting their red caps and tales. I had to build a basket from plastic fence and separate orandas in it in part of the pond where koi can't get to them. After couple of months i let orandas out in the pond and and seemed that aggression toward them stopped from koi. They were together for almost a year: from half of last summer and thru all winter until beginning of this summer I noticed that top of my orandas heads are chewed up again. Now my orandas back in the basket. It's really weird that my old timer koi never ever pay attention to orandas and new comers attacked them at first then letf them along then started to attack them again.