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Koi Ponds in Autumn – Maintenance and Dietary Changes

Hello, Frank Indiviglio here. As fall arrives in the temperate zone, outdoor koi ponds will need some attention if all is to go well when the temperatures drop.

Basic Considerations

Japanese water gardenThe metabolisms of both koi and the various bacteria that occupy the pond and filter slow down as temperatures fall. Your fish will not be as hungry as usual, and leftover food will not decompose as quickly as in the summer. Dead plants and other organic material in the pond may also remain more or less “intact” through fall and winter.

However, don’t be fooled by the relative “quietness” of this time….as temperatures rise in the spring, decomposition will begin and the resultant ammonia spike may kill your fishes. Therefore, take care to be extra vigilant in removing organic detritus from your pond as fall approaches.


Be sure that your pond filter is in good shape and running well…rinse or replace filter media and continue with routine backwashes.

If necessary, install a leaf cover or net. This is not merely an aesthetic consideration…decomposing leaves will rob water of oxygen, lower the pH and increase the ammonia level.

To control the amount of dead plant material that enters the pond, remove any aquatic or emergent plants that will not survive the winter.

Health Checks

It is especially important that your koi be in good health as the weather changes. Immune systems will be stressed by the falling temperatures, leaving the fishes open to illness and parasitic infection. Bacteria and fungi that are ever present, and may be of little concern to healthy fishes, will prove dangerous to those not in the peak of condition during the fall and winter.


As fall progresses, switch your koi from high protein pellets to more easily digested foods or wheat germ based pellets designed for use in cool water. Do not feed your fishes when temperatures drop below 52 F.


Make sure that heaters or surface de-icers, if required, are in good working order. If you utilize a heater, set its thermostat for 62 F. Koi will feed lightly at this temperature, but keep an eye out for leftovers. In unheated ponds, cease feeding at 51 F.

Further Reading

For optimistic readers already thinking spring’s arrival, please see our article Koi, a Matter of Extremes in Spring.

Please check out our koi and outdoor pond books for further information.

For interesting forum comments and photos dealing with overwintering koi under extreme weather conditions, please see the forum at koi-bito.com.

Please write in with your questions and comments.

Thanks, until next time,

Frank Indiviglio

Japanese water garden image referenced from wikipedia and originally posted by Solipsist

Koi: To Feed or Not to Feed and A Matter of Extremes in the Spring

Anyone who keeps a koi pond in cooler temperatures has been there. You start getting a few warmer days in late March and your koi, who had been inactive all winter, begin to swim around and look for food. Being the “good” koi keeper you are, and just an all around nice person, you start feeding your hungry friends almost immediately. The feeding continues to increase, while your pond continues to get greener. Meanwhile the local garden store is getting in a load of excellent looking Asagi or Shiro Utsuri Koi direct from Japan next week, and though you already have a questionable number of little Koi in your 1000 gallon pond, one more couldn’t hurt, right?

Pond keepers are creatures of extremes and it’s nothing we’re ready to apologize for (I mean, koi are soooo cool!). But, from a biological balance perspective, it’s really easy to start tipping the scale in your pond in favor of algae and unfavorable health conditions, particularly in the cooler weather.  

Believe it or not, koi in an outdoor pond do not have to be fed to survive. Being the scavengers that they are, they’ll have no trouble finding the nutrients they need among the detritus, bugs, and general wild things that end up in your pond throughout the season. What this means to you is everything you add to the pond, whether it be more fish, fish food or plants, adds to the nutrient load. In early spring, this nutrient load is particularly important for several reasons. First, your beneficial bacteria are not yet running full steam. This means ammonia takes that much longer to break down. When you combine that with the fact that your fish, and their immune systems, are still in slow motion due to the cooler water temperatures, a high nutrient load can cause problems. In addition, the natural “nutrient sucker-uppers,” your aquatic plants, are also struggling to gain a hold for the new season, so that part of your natural filtration is crippled as well.

Many koi keepers than ask, how can I get around this problem? I love my pond and I’m not going to stop feeding my koi, and I’ll probably add more fish to the nutrient load from time to time because they’re too awesome to pass up. Our response to you: avoid the extremes. Be sure to have the necessary test kits on hand to make sure levels remain nominal throughout the season. If you start to see problems, just like in an aquarium, try a water change, or add some bottled bacteria to help the chemistry settle. If your pond starts to get cloudy or full of algae, try adding more plants, or cutting back a few feedings. If you’ve tried all of these solutions and the problems are not going away, it may be time to consider a larger filter system or (gasp!) trimming your koi stock a little.

Good luck with your pond this season!

A Brief Intro to Koi

Patty here. Koi  are basically colored Carp.  They are descendants of Asian and Central European Carp originally domesticated and used as food in China and Southeast Asia.  Their hardy nature and adaptability made them easy to propagate and transport to new locations.  Beginning over a thousand years ago, Asian breeders were selectively breeding these fish to develop natural color mutations into the brilliant and brightly colored fish that exist today. By the early 19th century through the early 20th century, desirable color patterns were established by the Japanese, and Koi started gaining world -wide popularity. 

As Pond season rolls around this year, many might be considering the addition of Koi to a water feature. Here are a few tidbits to think about before you purchase koi.

  • Koi should only be housed in ponds at least 1000 gallons or more. The bigger the better. The depth of the pond should be at least 3 feet to help the fish to avoid overexposure to sun and heat and to allow them to survive harsh winter temps. If your pond does not fit these criteria, goldfish and comets will be a better fit for you.
  • The bright colors shown by koi make them beacons for predators. Herons, raccoons, bears, and even cats and dogs amongst others may find koi a fancy meal if they can reach the fish. Proper depths and shade trees can help the fish to stay safe.
  • Koi have big appetites. They are omnivores, and will enjoy a varied diet of staple pellets along with frequent treats of fruits and veggies like watermelon, peas, lettuce, and corn. Koi will also eat plants at the surface of the water and will happily dig at the roots of potted plants on the pond too. You may need to cage the plants to preserve them, or at least top the soil with river rocks.
  • By encouraging these fish to the surface for feeding, they can become quite tame, often hand feeding. This behavior allows for visual health inspections that may need to be treated.
  • Koi should not be fed if the temperature of the pond sees a constant of 50 degrees or lower as they cannot properly digest proteins.
  • Along with their big appetites comes a lot of waste. Be sure to provide ample filtration and aeration particularly if you have a number of these fish in a minimally sized pond.
  • If provided with a proper environment, koi can live for decades, and have even been reported as living more than 200 years!
  • Wild carp can grow to almost 6 feet in length, and ornamental koi are known to reach lengths of about 3 feet in length. Carefully consider this in relation to the pond you plan on housing the fish in as they grow QUICKLY! Juvenile fish can double in size in a year, and though the growth rate can slow after 2 or 3 years, the fish continue to grow for 10 to 15 years. They’ll need plenty of space to grow and live comfortably.
  • Koi spawn in the spring. Females grow bloated with eggs and males compete for the opportunity to fertilize the eggs when she releases them. You may see one fish being chased aggressively around the pond by several others. The female is the target of the attention. Supply breeding mats, floating plants, or plants at the bottom of the pond as a place where she can release her eggs. You may be lucky enough to see new additions to your population not long after, though survivability is usually not high unless the fry are collected and nurtured.

Koi can be the pride of a backyard pond, but they do require a bit more attention and a lot more space than goldfish and comets.  When you’re ready to add fish, give us a call or shoot us an e-mail with any concerns or questions so we can help you to have a successful pond experience.  Be sure to save the date for or annual Pond Festival, too, May 16-17 2009!

Image referenced from Wikipedia and originally posted by Stan Shebs

The Name Game, Part 3: Koi and the Japanese Naming System

In past blogs (here and here), we’ve gone over the basics of the Latin scientific naming system. Now, with spring and pond season just around the corner, it’s time to discuss a different naming system – Japanese Koi Nomenclature. Koi are considered some of the most valuable ornamental fish in some parts of the world and mature show quality koi can sell for hundreds or even thousands of dollars much like purebreed dogs and horses. Though other countries raise and produce koi, a Japanese emperor was believed to be the first to begin the practice of keeping koi in ornamental ponds and led to the breeding traditions practiced today. Koi are still usually referred to by their Japanese names for color and pattern.

Like the Latin naming system, the color of the fish plays a large part in the naming system and can point to more specific details in a larger group. For example, Bekko koi are fish that have black markings on a white, red or yellow background. Ki Bekko koi refer to those with a yellow background (“Ki” = “yellow”). The term “hikari” in koi names is also used to refer to a metallic sheen to the scales. Some color terms commonly used for koi are:

Red (Background) “Aka”
Red (markings) “Hi”
Orange/Red (background) “Beni”
Orange “Orenji”
Yellow “Ki”
Pale Yellow “Yamabuki”
Green “Midori”
Blue “Ai”
Brown “Cha”
Gold “Kin”
Silver “Gin”
Grey “Nezu” or “Zezumi”
Black (background) “Karasu”
Black (markings) “Sumi”
White “Shiro”

The most common Japanese terms that are used in reference to koi are those that refer to the pattern on the fish. The most common varieties are Kohaku, Sanke and Showa but there are over 15 commonly-used varieties and each of these can be broken down farther into color variations within that pattern or through lines developed by various breeders.  Some of the most common varieties are:

  • Kohaku – Kohaku koi are white with red markings. High quality Kohaku are pure white with no yellow in the coloring and have a deep, solid red color in the markings.
  • Sanke – Sanke is one of the most popular varieties. Like the Kohaku, these koi are white with red markings, but Sanke koi also have black markings superimposed on the red and white. High quality Sanke may not be symmetrical in their coloration, but the color should be distributed over the entire body, except for the head.
  • Showa – Showa koi are very similar to Sanke but can have much more black on their bodies. The black can be anywhere on the body, including the head, sides and belly (considered undesireable for Sanke koi). Hi Showa is an example of a subvariety of the Showa koi with more deep red color than others.
  • Asagi – Asagi koi are one of the most distinctive varieties (and my personal favorite). These koi have blue bodies, white heads and red markings in the tail, fins and face.
  • Bekko – These koi have black markings with a white, red or yellow base color. The name of the color is usually used to determine which type of Bekko a fish is (Aka Bekko, Ki Bekko, or Shiro Bekko).
  • Goshiki – “Goshiki” literally means “5-colored”, in this case light blue, dark blue, red, black and white. The markings are colored over a white background. This variety can be highly variable in appearance.
  • Hikari Utsuri – These koi have the same pattern as Showa and Utsuri koi, but have a metallic sheen to their scales.
  • Hikarimoyo – These koi are also metallic but are made up of the metallic koi that are not Showa or Utsuri. Hariwake is a popular variety within this group; this subvariety is metallic silver with orange or yellow markings.
  • Hikarimuji – Hikarimuji is another metallic variety but these fish are all one solid metallic color. Pure-colored metallic koi within this category are also known as Ogon koi, leading to the popular Yamabuki Ogons (pale metallic yellow) and Platinum Ogons (pure white and metallic).
  • Kawarimono – This variety is like the Hikarimoyo variety in that it included all fish not included in the other popular varieties, but koi within this group can also be divided into their out categories describing their breeder lineage, color or scale traits. The terms “Gin Rin” (meaning sparkling scales) and “Doitsu” (referring to fish that are otherwise scaleless except for mirrored scales around the dorsal fin) are used more in this variety than most others.
  • Koromo – Koromo koi are similar to Kohaku, but the scales of the red pattern in Koromo koi have dark edges, leading to an almost crosshatched pattern on these markings.
  • Tancho – Tancho koi can sometimes fit within the Kohaku, Sanke or Showa categories, but the markings in Tancho koi are more specific. Tancho koi are white with one red patch on their head, preferably as circular as possible. Tancho Kohaku are the most popular with their pure white bodies and one red patch, but Tancho Sanke and Tancho Showa koi are also popular.
  • Utsurimono or Utsuri – These koi are in some ways the opposite of Bekko koi. Instead of having black marings on a colored background, Utsuri koi are black with white, red or yellow markings. Shiro Utsuri, the black and white variety, are the most common, folowed by the more rare Hi Utsuri (red and black) and Ki Utsuri (yellow and black).

This list is far from all-inclusive of all the koi varieties and patterns but can give you a good start in learning the difference between all of the varieties available. As this list demonstrates, koi are some of the most collectible and carefully-bred fish around with a history going back hundreds of years. Koi and pond care can open up a whole new frontier for avid aquarists and the time to start planning your new pond or new pond additions is here! Chart referenced from Wikipedia here.

Uncommon Facts About Common Aquarium Fish

I’d like to take time to welcome Frank Indiviglio to That Fish Blog. Frank is a former Bronx Zoo Zoologist, author and conservationist who’s worked with everything from fish to elephants. He’ll share his unique insights and work with various species on here, as well as the newly created That Reptile Blog & That Avian Blog. Welcome Frank!

Today I would like to pass along some interesting facts concerning fish you may be familiar with. I’ll focus mostly on aquarium trade species, with a few others added for good measure. I’ll add to the list in future articles. Enjoy, and please share your own store of unusual facts with us.

Finding a mate in the dark, featureless expanses of the deep sea poses quite a difficulty. Male benthic anglerfishes, such as Ceratias uranoscopus and related species, solve this dilemma by biting onto the first female they encounter. Thereafter, the male’s internal organs degenerate and he remains fused, by his mouth, to the female – surviving on nutrients circulating in her blood and periodically releasing sperm to fertilize her eggs!

Unique among the world’s fishes, male sticklebacks (small fishes of the family Gasterosteidae that inhabit marine, brackish and fresh waters), use kidney secretions to glue plant materials together when constructing their enclosed, bird-like nests. This behavior, along with their zealous protection of the eggs, helped spur the development of the aquarium hobby in Europe in the 1700s.

Cichlids found in Africa’s Lake Malawi are among the most enthusiastic of nest builders. Although measuring but 6 inches in length, males of one species create circular sand mounds that can exceed 3 feet in diameter, while another excavates 10 foot wide pits. Up to 50,000 such structures may be constructed in the same general area by a displaying group, or “lek” of males.

Marine damselfish, such as Stegastes nigricans, are unique in practicing a form of underwater “farming”. Pairs form territories around beds of marine algae (“seaweed”) and drive off fishes, shrimp, crabs and other creatures that show interest in this favored food.

Clownfish, such as the commonly kept percula clownfish, Amphiprion percula (or its cousin, the false percula, A. ocellaris, of “Nemo” fame) live unharmed among the tentacles of sea anemones — marine invertebrates that sting and consume other similarly-sized fishes. Anemone tentacles respond with a sting upon contact with any alien body, but are prevented from stinging themselves by chemicals in the mucous that they secrete. The clownfish, it seems, produces the same chemical in its own mucous and hence is not recognized as food.

Fishes lack external ears but do have inner ears that pick up the water pressure changes which accompany sounds. Aided by the Webarian Apparatus, an organ that connects the
inner ear to pressure-sensitive gas in the swim bladder, species such as carp and goldfish hear quite well and can communicate through vocalizations (perhaps it is not so odd to talk to your pet after all!).

Among the animals that are kept by people for their fighting abilities, none are as small as brackish-water fishes known as wrestling halfbeaks, Dermogenys pusilla. These thin, 3 inch-long warriors are the subject of staged matches in betting parlors throughout Thailand and Malaysia. Fights rarely result in injury, except to the wallets of losing bettors!

Despite popular belief, koi, Cyprinus carpio and goldfish, Carassius auratus, are not closely related. Goldfish, the first of any fish to be domesticated, were first kept by the Chinese over 2,000 years ago. Koi (the word means “carp” in the Japanese language) originated in the Black Sea area and arrived in Japan as a food source. They were first bred for domestic traits in Nigata, in northeastern Japan, in the 1820’s.

Ichthyologists discover new facts about fish on a near-daily basis. You can read articles about their findings at:

Thanks Frank,

Until Next Time,