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Don't ignore the signs

If your koi are acting strangely - they may well have a health problem. Don't ignore the signs when your koi tell you they are ill.

Disease diagnosis

When health problems strike, an early, accurate disease diagnosis is vital. If caught early enough most disease outbreaks can be resolved quickly and simply. Looking for the warning signs that your fish have a health problem is simple - if you know what to look for!

They can't talk

Unlike for other family pets, it is very difficult for fish to let us know when something is wrong. They cannot whimper or limp when they are in pain or refuse to get up for food or exercise. We are unlikely to know if they have 'diarrhoea' or some digestive disorder and we can't readily examine them for parasites or skin disorders. Because we cannot rely on them to let us know when they are ill we have to be pro-active and constantly look for health problems, rather than waiting for them to become apparent. This means that once or twice a week throughout the season (less in winter) we should set aside time to make a thorough check.

A major problem seems to be that while we spend many hours admiring them, it is very difficult to look beyond the dazzling colours and appealing faces. However, it is important that we do take time to look for problems before the problems find us.

Behavioral changes

During these visual examinations we are looking for changes in behaviour and physical appearance. Any changes from normal should arouse our curiosity. For example:

  1. They may not be feeding. Make sure they are swallowing food and not just mouthing and then rejecting it.
  2. Is the fish swimming alone, deliberately staying away from others
  3. Is it lying on the pond bottom or hovering near the water surface or water return for long periods?
  4. Is it breathing heavily or unevenly? This can be determined by checking the rate of operculum (gill cover) movement when compared to other fish in the pond
  5. Look for fish using only one pectoral fin, with the other clamped to its side. The pectoral fins are the 'paddling' fins, on each side of the body just below the gills
  6. If they rub against the pond-side or bottom, or regularly leaps out of the water, this is usually a sign of irritation and not playfulness or an attempt to catch flies
  7. Do they seem jumpy or nervous?

These changes in behaviour should be easy to detect and warrant, at the very least, the affected fish should be kept under very close observation. If just one or two seem to be affected, keep a close eye on them for a day or two. This allows for the fact that even fish can have 'off' days. If the abnormal behaviour persists, further investigation is needed. If several or all are affected then it is likely that there is a serious problem needing urgent attention.

The relatively high stocking levels of most ponds increases the likelihood of problems and calls for a higher degree of vigilance on the part of the owner if problems are to be avoided or dealt with quickly and effectively. Being observant and noticing the telltale signs that indicate something is wrong is the most important aspect of disease prevention in any animal.

Physical changes

A common problem in koi keeping is the failure to spot physical changes and injury early enough, leading to many fish succumbing to serious bacterial or parasitic problems that could have otherwise been treated successfully earlier.

I recall one, not uncommon incident, when I was asked to examine a couple of fish in a pond. Closer examination showed that out of twenty-four fish, sixteen had body ulcers! Given the severity of some of the lesions it was obvious that these problems had existed for some time, but the owner had not noticed

We need to examine carefully the integrity of the fins and the condition of the skin, with any noticeable changes being cause for attention. For example:

Fins are often the first body part to deteriorate when fish are stressed or unwell so they can give a good general guide to condition. Examine all fins, especially those underneath the fish, for ragged or uneven edges, tears, splits or bloodshot appearance. Invariably, these conditions indicate a bacterial or environmental problem needing urgent attention and do not result from fish ‘nipping’ each other.
Check for any thickening of the mucous layer or cuticle, especially around the head and upper body surfaces, giving a milky or grey appearance to the skin. This could indicate a parasite problem
 Look closely for any reddening of the skin, abrasions or open wounds, particularly at the base of the fins, around the mouth and on the underside of the body. This type of damage often indicates a bacterial infection and only rarely results from bumping into rocks, pipes etc.

While not an exhaustive checklist, the above covers most typical clinical signs and should help with early detection and prevention of many common problems. When accessing the severity of a wound or lesion it is important to bear in mind that things often look very much worse out of the water

Take your time

In the belief that prevention is better than cure, time should be spent quietly observing the fish from a position that allows us to see all the body parts, particularly the often hidden underside where so many problems seem to occur. This is often best achieved by watching them as they come up to feed, which gives a good view of the mouth and area under the neck, down to the underside of the pectoral fins.

The rear underside, including the important lower fins (anal and pelvic fins) and the area near the base of the tail fin can often be seen by viewing the fish from the side rather than from the top. This is best done by looking at them from water surface-level as they swim by the opposite side of the pond, which is easily done with a raised pond but not so easy with a ground-level pond. If there is a suspected problem it can be confirmed by 'bowling' the fish or putting it into a polythene bag for closer examination.



Fish disease problems? Need some help? The help pages take you through the basics of the 'fish health work-up' diagnosis method and basic fish disease treatment methods.

90% of all health problems and fish deaths are caused by poor fish keeping! The key pages are essential reading for all beginners and intermediates who are serious about disease prevention.

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Expanded Content by Dr. Erik Johnson, DrJohnson.com and Used with Permission; Frank Prince-Iles ©2009 All Rights Reserved