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Chris on Koi

The Immune System of Koi - Further Studies

I submitted this article some years ago to KOISA. There is much valuable information for new members of the Society so I request the editors to re-publish this fascinating essay.

Although the following essay demonstrates the effect of hormones on the immune system, other hormones can have an effect on the growth of koi. If a koi does not grow in your collection, experiment by removing it to another pond, if possible. If it starts to grow then you know that the hormones from the other fish were affecting the growth of that particular fish. If it does not grow then one of two things has happened - the genetics of the fish has dictated the size of the fish or the fish is older than you know or realise. Just as in all creatures, growth hormones stop after a certain age and the creature stops growing (unless you are a body builder and munch on your daily hormone). (does that sound right?).

A study by Perimutter, Alfred, Daniel Sarot, Man-Lin Yu, Rocco Filazzoia and Seely on the Effects of Crowding on the Immune Response of Fish indicates that there are "other" hidden factors at work than first meet the eye.

These are not readily visible or apparent to most koi keepers. Sometimes we simply notice that our koi die without explanation. Perhaps the study by Perimutter et al can throw some light on this phenomena.
Their study may indicate that fish kept in overcrowded conditions suffer impaired immune systems as a result of biochemical agents released into the water by the other fish living in the pond.

This may be natures way of reducing a large population to more acceptable levels. The studies suggest that fish can release immune suppressing pheromones (hormones) in overcrowded conditions. This makes the other fish in the system less able to fight disease.

To investigate their suspicions three separate experiments were set up. These involved different treatment and control groups.

The first two experiments had 30, 15, 5 and 5 fish respectively. Four similar control groups were set up. Fish were assigned randomly among the groups. All ponds were the same size.

The water in the treatment groups had methylchloroform added to remove organic substances. The control groups were not treated but simply monitored.

Ammonia, nitrate, dissolved oxygen, carbon dioxide and pH were monitored regularly.
The immune systems were challenged with infectious Pancreatic necrosis virus. All fish in the treatment and control groups were injected with the virus two weeks after the experiment began. Two week later they were injected again.

The researchers made antibody tests. These antibody measurements showed that maximum antibody reaction occurred three weeks after the second injection of the virus.

Looking through the results shows that the fish from the experimental groups had two to four times the antibody levels than the fish from the control groups.

As the level of crowding increased so the difference between the groups increased. The implication was that the methylchloroform was removing something from the water that affected the fish immune response.

This unknown factor was directly proportional to the crowding level. The greater the crowding level the greater the immune suppressing effect. The evidence suggested an immune suppressing pheromone was present.

To check their findings the authors then decided to refine a third experiment. This third experiment was run twice with each of the four treatment and control groups. These being 30, 15, 5 and 5 fish again.

The results were as follows.
  1. The groups of fish at low stocking densities had twice the antibody level of the control groups.
  2. The groups with slightly higher stocking densities had four times the antibodies present.
  3. However, as the stocking densities increased the effect of the immune suppressing agent became more pronounced. There were less and less antibodies recorded in the test groups.
  4. It is worth noting that even at low stocking densities there was a lower antibody count. This indicates that even at low stocking densities there is immune response suppression.

Conclusions: Low stocking densities can help minimise bacterial and viral disease problems. It is presumed that the fewer the fish in the water the less the concentration of pheromone present that suppress the immune system.

The lower the stocking density the lower the bacterial load on the pond.
The offending pheromone can be removed with proper chemical and physical techniques.

Water Changes
The importance of water changes should NEVER be under estimated. Regular water changes will dilute the biological 'soup' the fish swim in. The higher the stocking densities the greater and more frequent the water changes should be. To save water, utilise the pond water for watering the garden then supply the fish and pond with fresh water. Both will benefit as will your pocket. You can created a mini eco-system on your property.

The use of activated carbon has been shown to remove organic agents such as pheromones.
Skimming the frothy bubbles or scum that forms on the surface of the pond (Dissolved Organic Compounds or DOC) from time to time will also lower the level of pheromones. The DOC should be removed from the system and not simply skimmed back into the filter. The amount of scum or DOC is important when the fish load is high. This should be removed from the system.

A last consideration. Perhaps we should select and remove koi from our collections regularly. As they grow and as we add new ones to the system voluntary removing the old ones which are not of good quality will have positive results.

1. The collection will be continually up-graded and improved. 2. The collection will be selectively 'culled' by the owner and not by mother nature taking things into her own hands when disease breaks out in overcrowded ponds.

Chris Neaves

Last Updated on Friday, 31 October 2008 12:15