FEBRUARY/MARCH ~ Measuring Clarity. Tying Food. To Water Quality. Collection of young and old pharyngeal teeth

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Rosemary Morrison
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Collection of young and old pharyngeal teeth Something that we never find in hobbyist books is how our Koi actually eat their food and why they like certain foods more than other foods.

2 Collection of young and old pharyngeal teeth Something that we never find in hobbyist books is how our Koi actually eat their food and why they like certain foods more than other foods. With some effort, you can find this information by looking through scientific papers. In this article, I will describe how our Koi handle their food intake.. There is something else to consider when we are feeding our Koi. vve like to have crystal clear water for our Koi and that is almost a contradictory statement. When the Koi are very hungry we give them more food, which generates more waste. Measuring Clarity What is actually the definition of clarity? Most Koi keepers would say that it is being able to see the bottom of their pond,.pthers would say the lack of particles in the water creates clear water. Luckily, there is a norm for clarity, more precisely the lack of clarity or turbidity. The nephelometric method compares light scattered from a water sample to light scattered from a reference. The unit of measure is the Nephelometric Turbidity Unit (NTU). In Image 1, you can see several NTU calibration fluids ranging from 0.02 NTU through 10 and 100 to a 1000 NTU sample that looks like milk. Using these calibration standards, you can calibrate a digital NTU meter to get accurate measurements. A not so ~ lear pond would have an NTU figure of around 1.5 to 3. A very clear pond would be below 0.9 NTU. An extremely clear pond can give a value of 0.3 to 0.45 NTU. So why am I so interested in these values? Koi food may break down into smaller pieces when it becomes wet. The Koi grind the food and spit it out if they do not like it. Koi feces is not very solid and tends to create smaller pieces. All of these things affect the clarity. To determine how much, we need NTU equipment to get an accurate measurement. Food can color the water, too. This has to do with the vitamins in the food that release straight away in the water. Some foods can actually create a lot of color in the water. The simplest test for this is to put some pellets into a glass of water. After an hour look to see how much the color has changed. If you usc very good foods, the discoloration will be very low. With lower cost foods, you could get more color in the water. After an hour, you could even see the pellet fall apart into smaller pieces creating waste at the bottom of the glass. This is something that you do not want to see because it will influence the clarity of your pond water. Therefore, it would be good if we can feed a solid pellet that stays intact after a longer contact time with the water and does not quickly release its vitamins and proteins into the water. Tying Food. To Water Quality For the best water quality, feed a pellet that does not quickly release its protein because this creates an oily film on the top surface of our pond water. The pellets should keep their vitamins well bonded so that we do not color the water. Be sure that the Koi eat the food as fast as possible to minimize the leaching of protein and. vitamins into the water. This also helps the Koi benefit from the full potential of the food while reducing the chance that the pellets will break down into smaller pieces. The most important factor is that the taste of the food is attractive enough that the Koi will not spit it out. Another consideration is the food's hardness, how easy it is for the Koi to crush and grind the pellet. We want to reduce the amount of small particles that could rinse back into the water. As you can see, there are many requirements on the foods we feed our Koi because we want to have the very best water quality for our Koi. FEBRUARY/MARCH ~

3 G) KOI NATIONS

4 Image 1: Fluids to calibrate an NTU instrument. Left, 0.01 NTU, Right, 1000NTU. Image 3: Old pharyngeal teeth with deep grooves. In aquaculture, we would find these less important because the food conversion and growth rates are much more important. However, good food conversion rates are important for our Koi too because high conversion rates mean less waste and better water quality. Therefore, it would be good to know how Koi find and process their food in mudponds. In general, there is not mllch research done on Koi but they are almost the same as carp, described in the literature as cyprinus carpio. and the size of small plankton in the water. Most Koi between 20-50c111/ in would have a min imal mesh width of 400 to 500 microns. They clamp the food between the palatal organ and the branchial sieve and wash away the smaller particles through the branchial sieve back into the pond water. Koi can backwash their branchial sieve to clean it and push larger particles back to the buccal cavity for more filtering. This process we call resuspension with a closed mouth. Utilization Of Food Resources In 1987, Mr. F.A. Sibbing of the Department of Experimental Animal Morphology and Cell Biology at the Agricultural University in Wageningen wrote a paper about how carp utili ze different types of food. Carp are actually very smart because they can separate the nonfood from the food that they need. Can you imagine how they The color of teeth also says something about the health of the Koi. The whiter the teeth the healthier, they are. would separate the detrims (mud) from the benthic invertebrates that they are gulping from the bottom of a mud pond? Carp intake water and mud at a certain speed so that they intake only the top part of the mud because this layer has a higher concentration of food for them. The Koi's palatal organ filters the food fi'om the mud. This organ can separate benthic invertebrates smaller than 4% the diameter of the total length of our Koi. The Koi process very hard food with their strong pharyngeal jaws set with several pharyngeal teeth. They can also process zooplanktons th~~ are bigger than 250 microns. They are very li mited in processil1g long and struggling prey because the carp or Koi do not have oral teeth. The specialized morphology of their pharyngeal chewing apparatus makes it almost impossible for them to eat other Koi or long vegetative plants. Functional Morphology Functional morphology is not easy to explain in simple words but we will start with the mouth where the Koi would take in its pellet. The pellet enters the oral cavity and moves to the buccal cavity. Then it wi ll come into the pharyngeal cavity where we have the palatal organ and the branchial sieve to separate the nonfood from the food. From there the pellet would reach the chewing cavity for processing before going into the esophagus. Palatal Organ And Branchial Sieve This part is a very clever method for the Koi to separate food from nonfood. It works as fo llows. The branchial sieve has gill arches with giijrakers that create a mesh between 250 to 500 microns depending on the taste buds that the Koi has on its palatal organ Chewing Pad Because the Koi do not have oral teeth, it is almost impossible for them to capture and hold struggling prey and move this prey into the chewing pad. In the chewing pad there are several pharyngeal teeth but as you can see in Image 2, they are quite flat. Only the bigger ones have some grooves in them (Image 3 ). Then the size of the chewing pad that you can see in Image 3 allows only particles smaller than 4% of the length of the Koi. If your Koi is 70cm/27.5in long then the particles need to be small er then 2.8cm/1 in but when the Koi is 25cm/9.8in long this is only 1 cm/3/8in. Food Intake The particulate intake method of eating is the most valid one for pellets that we are giving our Koi. In this mode, the protrusion of the upper jaw forms a rounded suction tube that creates a fast suction flow to catch the pellet. Detailed maneuvering of the body is important to get the pellet but fast swimming plays a mil~o r role. Most of us feed our Koi pellets so the particulate intake is the most important method. However, this would be different in a mud pond. The second method is gulping the food from the bottom of mud ponds. This allows the Koi to stay horizontal so that they can escape quicldy from predators. Using this method, they cannot take in particles bigger than 7% of their body length. This is valid for Koi bigger then 25cm/9.8in. The suction flow here is much lower than with the particulate intake and is very efficient filter for smaller particles. Selection And Rinsing Here we can talk about size selection by the branchial sieve described above and about taste selection. Carp feed on benthos, organisms living at the pond bottom, and practice selective retention. The Koi performs selective retention by first clamping ingested material between the pharyngeal roof and pharyngeal floor. They then wash the small waste particles away through the branchial sieve. The pharyngeal roof has a very high concentration of taste buds FEBRU ARY / MARCH G)

Image 5: At the bottom you can see the papila and in the background you can see the horizontical split shape on top of the palatal organ; Image 6: Bottom view that shows you the internal part of the

6 Image 5: At the bottom you can see the papila and in the background you can see the horizontical split shape on top of the palatal organ; Image 6: Bottom view that shows you the internal part of the Koi; Image 7: Here you can see the posterior pharynx; Image 8: Here you can see the anterior pharynx; Image 9: Cross section of EAone food that have stayed for a long time in the water. on the oral papilla, about 820 per square mm. This is one of the highest concentrations for a Koi. In Image 5, you can see the papilla at the bottom and in the background the horizontal split shape that is on the top the palatal organ. Below this are the gill arches that you cannot see. The taste buds help the Koi determine which ofthe clamped particles it wants to keep as a food and which it wants to flush away. The Koi spits out nonfood or unpalatable materials. The Koi backwash many times with their mouths closed to achieve a better separation offood from non-food. Repetition allows taste selective retention to do its work better. In this way, they can extract more of the zooplankton, a beneficial food source for the Koi, from the branchial sieve. Transport, Mastication Following selection and rinsing, the Koi moves the food to the chewing cavity for mastication. Here they compress, slide, or bend the pellet to increase its surface area. Increasing the surface area of the food reduces the energy needed to digest it. Because Koi are not very good at crushing and grinding, they only fl atten elastic and soft pellets. This depends on mechanical properties like hardness, stiffness, and elasticity that we find in different pellets. The surface area of the chewing pad is quite smooth. The profile of the chewing surface of the pharynael teeth can be quite different The most important factor is that the taste of the food is attractive enough that the Koi will not spit it out. depending upon the age of the Koi. It may be ve ry smooth when they are young but older ones can have grooves in theo~.. The dorsal and ventral muscles transfer the force to pl1aryngeal jaws by li fting the skull and retracting the pectoral girdle. This com bination creates very high mastication pressures that can crush very hard grain. This can even be heard when you put a microphone in the water. The Koi use their other muscles to stabilize masticatory movement. When finished chewing, they compress the chewing area to create a deglutition, swallowing action. By repeating this they move the food into the esophagus. Losing Teeth The high pressures and complicated movements of feeding can sometimes cause the Koi to lose teeth. This is especially true when their pellets are very hard and need very high forces to crush. My friend Barbara Johnson has a very big collection ofteeth that she has found in baskets of pumps and in skimmers, (Image 2, page 47). It was a shock to find this amount of teeth. It seems Koi lose more teeth than I thought. We have done extensive testing with different types of food and sti ll found many Koi teeth. The color of teeth also says something about thc health of the Koi. The whiter the teeth the healthier they are. Pellet Hardness Polychaetes are a very strong binder that can make the food hard after cold processing. The hardness of the pellet depends upon the amount of polyc haetes in the food. More open spaces in the food make it is easier for the Koi to masticate the food. When testing the food, we used NTU levels as a guide to determine the best formula for water clarity. In the end, we had the perfect combination of polychaetes in the food to create the right hardness of the pellet. Eating speed is ve ry important because we want the Koi to absorb all their food's good vitamins and proteins without losing them in the water. It can take two to three weeks for the Koi to adjust when you change their food. Some Koi keepers try to mix the food but I choose not to do that. The simple reason is that they will eat all the foods that are using sugary ingredients to make the food more attractive first. Koi are just like chi ldren, they like to eat sweets first before a healthy meal when they can choose. Softness And Texture As described before, Koi have taste buds on their oral papilla and can quickly find the difference between different types of foods. It is almost like our tongue that can determine the difference in taste and texture. Of course, the Koi cannot speak but it is ge nera ll y known that carp or Koi would prefer soft textures. Therefore, it is important that their pellets quickly soften in water to become more attractive for them. As an added bonus when the texture is soft the Koi does not need to regrind its food so many times. Chew On This There is a lot more in formation than we can fit in this one article. I have tried to make it as simple as possible so that everyone can understand. The food intake and intra-oral food processing really depends upon the sensors that the Koi have and how the Koi separate food from non-food. This is more advanced than you would think at first. It was difficult to find this kind of information but it does help us understand the relationship between clarity, food conversion, and the behavior ofkoi when they are eating their food. In the next article, I wi ll discuss feeding frequency versus protein intake. iii ~ I ~"" ~ ~ Jasper Kuijper lives in the UK and has been a Koi keeper for more than 20 years. He is the Commercial Director for Evolution Aqua. To reach him, writers@koinations.com. FEBRUARY / MARCH EI)

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