Ulcers in the koi.Logo of Asia USA Realty

Feeding of koi in a heritage shophome pond.

Last updated:
13 Dec 2001
Tail ulcers in a koi ULCERS IN THE KOI

The picture above shows 2 ulcers of the skin of the koi fish.  Click on the thumbnail photo to see bigger image.  The fish was isolated and recovered after treatment and plenty of loving care for the next few weeks.  Only this fish was affected, amongst others.  

"What are ulcers and how do we prevent them?"

Ulcers are open sores, other than wounds.  They occur on the skin or the mucous membrane of the body e.g. stomach or mouth and are  characterised by tissue breakdown and often, the discharge of pus. 

To prevent ulcers, one needs to know what causes ulcers and there may be several factors.   Stress at the office is said to be the cause of stomach ulcers in people.  The hot temperature and lack of adequate water may be a cause of mouth ulcers in Singaporeans.   Overcrowding has been said to be a cause of stomach ulcer in pigs.

What stress is there for a koi fish which just swim around daily?  The poor quality and aeration of the pond water will be a great stress to the fish.   Newly bought fishes with parasites may be introduced into the pond.  Itchiness may cause the fish to rub against the pond leading to breaks in the skin and ulcer formation.   It is best to isolate the koi with ulcers, examine the ulcers for parasitic or bacterial infections and treat it. 

Some ulcers are caused by viruses and bacteria are opportunistic secondary infections.   Therefore, the diagnosis of bacteria in the ulcers may not indicate that the cause of the ulcer was due to the bacteria. 

It is not possible to confirm viral infections using the ordinary microscope.  An electron microscope is needed and this is too expensive for almost all koi lovers who want to diagnose and treat their sick kois.  Singapore's veterinary laboratory at the Primary Production Department may be able to check on viral infections through cultivation of the virus and in histopathology of the cells taken from the ulcerated areas.


This report is written for expats who want to keep koi in their heritage houses and discusses the good feeding management of the koi.

The following are important tips which help to keep koi healthy.

1.      When should I feed the koi?
The temperature of the pond is important as fishes are cold-blooded animals.  When the temperature is less than 50 degrees Fahrenheit (10 degrees Celsius), less feeding is required by the fish as the metabolism of the fish is low.   Above 85 degrees Fahrenheit (30 degrees Celsius), the dissolved oxygen in the water will be in the low  range and feeding should be reduced.  Once a day feeding is sufficient for adult koi.

The temperature of the pond ranges from 50 degrees to 85 degrees Fahrenheit  or 10 degrees Celsius to 30 degree Celsius in temperate climates. In Singapore, the temperature will be closer to the 30 degree Celsius.    

In Singapore's heritage houses, the temperature of a small koi pond will be in the higher range.  Aeration of the pond is important.

2.     How much should  I fee the koi?
Feed commercial koi feed at 3% of the total weight of all fish in the pond.  Once or twice a day.  Feed from the same place if the garden pond is large, otherwise the fish will have to hunt for food and there  will be wastage.  Make sure all the feed is consumed within 30 minutes.   Do not feed more than they can consume.

3.     What should I feed?

Good quality and highly digestible feed is important.

Protein.  Essential amino acids need to be included in the part of the protein feed in your koi food. Lysine and methionine are amino acids needed by koi as well as other animals. 

Poor quality protein will not contain sufficient amino acids and will be used as a source of energy resulting in more ammonia being released in the pond and affecting the quality of water.   A high protein diet is essential for growing kois, as in babies and all animals.  For breeding koi, a high protein diet is also important.  Vitamin E is said to enhance fertility in the koi too as in people.

Carbohydrates will provide the energy. As koi are cold-blooded animals, they do not need a lot of carbohydrates to generate body heat on a continual basis.  Much depends on the temperature of the pond water as lower temperature means that the koi will not be so active and will need less feeding. 

Kois need a greater amount of vitamins than people because their digestive system is not highly developed.  Vitamins B, C and E are provided in most commercial koi feed.

How about snacks?  Fresh lettuce, celery, mangoes and oranges occasionally.   Live insects may be a treat but they carry the risk of introducing disease into the koi.

What are the ingredients of commercial koi feed?

Wheat germ is a natural source of Vitamin E.  Its high quality protein helps koi to grow faster.  Vitamin E is reported to be responsible for fertility and improve blood circulation.

Carotene in koi feed improves the red or orange colour of koi.

Spirulina algae brings out the natural vibrant colour.

Medicated food sticks contains drug such as malachite green and are used for the treatment of parasitic diseases such as ick, unicellular skin and gill parasites and prevents infection by free swimming parasites.  Usually the drug will not harm the other aquatic plants.

Brine shrimps are continuous filter feeders.  They can deliver food and nutrients to your fish through a process known as bio enrichment.  Some commercial koi feed contains brine shrimp.


In Singapore, children love to feed bread to the koi.  Bread should not be the sole diet.    A varied and balanced diet is important for your koi.  One type of commercial feed will not cover everything especially when the koi is growing or breeding.   The temperature, oxygen content and quality of your pond water must be ideal for the koi if you want them to survive.  Feeding at the same place everyday if your garden pond is very big ensures that the fish will not need to hunt for food and will get its daily intake.

A balanced diet promotes balanced growth and gives the koi resistance against diseases.   Adult kois in Singapore heritage houses will do well with one feed a day.

You do not need to bring the kois for a walk but you do need to ensure that they live in a well aerated and good quality water environment, free from parasites and infections.

Staying healthy, disease free and achieving maximum growth potential will make you enjoy the company of koi in your garden pond.  The beauty of the colours, the graceful swimming and the friendship bond between you and the koi - all these can only be experienced when you come back from a stressful hard day's work.

5-month-old koi in a quarantine tank in a Singapore commercial fish farm 3-month old koi fish in a Singapore commercial fish farm
The December 2001 pictures show healthy kois kept in quarantine tanks in a  commercial fish farm in Singapore accepting kois from breeders and then sold to dealers. 

This farm has many different kinds of ornamental fishes for export to overseas countries.  Fishes include eel, discus, tetras and others. The operator has over 30 years of experience.

50% of the water used is rain water and 50% is the water from the Utilities Board.   The water will be filtered and then ozonised.  The tanks have been stablised for a few months before being used for fishes.  Fishes put into a new cement tank will die.

The big tanks housing growing fishes have a side net to prevent birds from going inside to eat the fish.

There is a overflow pond in this farm receiving the excess medicated water.  This pond will drain out excess water into the sewerage pond which connects to the sewereage system.  The sick fish in this pond is said to recover from illness after some time inside this pond. The sun and low stocking rate may be help the fish to recover.     

The farm has a wide roads so that containers can reverse.  A big spotlight like those you see in a football stadium is installed for night business.

Commercial ornamental fish farming is a big and profitable business if you know how to do it.


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