Alan’s Book

Chapter 14 The Environment & Parasites in General

Parasites in koi ponds can often cause serious problems for the koi, and koikeeper alike. By this I mean that the fish have the parasite problem, and the keeper has the problem of curing it!

Knowing which parasite or parasites are present is essential for the application of the correct remedy.

In order to be able to control levels of fish parasites in ponds, it is necessary to understand something of their life cycles. Understanding how they reproduce, and what their various life stages are, can sometimes allow us an opportunity to seriously reduce their numbers.

Environmental Conditions

Problems with parasites are usually associated with either new introductions to the pond or some environmental problem such as low oxygen levels, nitrite or high nitrate levels or filter malfunction.

Low oxygen levels and are more likely to prevail in summertime, when temperatures are higher, some treatments for parasites can target algae and pond debris as part of the chemical reaction aimed at the parasites, and in so doing, create oxygen shortages.

It is wise to increase aeration in the pond before, during and after any medications are used. As fish consume approximately four times more oxygen after feeding, it is best that food is withheld for the duration of any treatment.

Simply overfeeding the fish can cause nitrite levels to rise above normal levels, or it can happen when the stocking level is in excess of that which the biological filter can cope with. Low oxygen levels and low KH frequently lead to nitrite levels rising. The whole pond system relies upon oxygen to function and adequate resources of alkalinity are essential to the bacterial activity of the filter. In systems operating in areas where the water is soft and winter and spring pond care is kept to a minimum in terms of water changes, the borderline level of alkalinity can be reached. If this happens, the increased activity within the pond can use up the remaining alkalinity and biological filtration problems can occur.

Nitrate is the end product of the biological filter function and can be controlled by regular water changes. Test kits are available for measuring all the water parameters mentioned.

Frequent parasite problems would tend to suggest that the environmental factors within the pond are less than ideal. Fish living in a pond with good water parameters are able to cope with the small levels of parasites, which are often present in small numbers in perfectly healthy ponds.

It is difficult to take any one subject, which is part of the overall scene of keeping koi, without the subjects overlapping with other subjects relating to the koi pond.

Low oxygen levels and nitrite contributing to a parasite problem – never!! Or so you may have thought before reading the above facts.

Many koi keepers are not aware that the koi’s immune system contributes significantly to parasite control; accepting this fact my help readers to understand the implications of temperature and water quality which also influence the efficiency of the immune system response.

At low temperatures very little activity occurs in a pond, bacteria, parasites and fish are all relatively inactive. However once temperatures begin to rise all activity increases. This can cause problems for koi because the increased bacteria and parasite activity are occurring before the koi’s immune system is able to react to this threat.

Bearing this in mind all koi keepers should ensure that parasites are controlled at all times and should be particularly vigilant in the springtime!

Signs of Disease

Most parasites will cause fish to react in a similar fashion. Points to watch for would include the following:

Fish remains alone and ceases to be a sociable shoal fish.

Fish jumping or scraping against pond side and floor.

Fish refuses to feed.

Fish breathes heavily, opening and closing of the mouth and gills.

It is possible to have parasites in a pond and only one, or a few of the fish seem to be affected. As individuals they can differ in personality as well as their ability to resist disease and parasites.

If this is seen to happen, it is possible to treat an individual by way of a salt bath. Seawater contains about 3% salt. The bodies of freshwater parasites contain about 0.5-9 % salt solution. Osmosis is a simple physics fact which guaranties that water will always tend to go towards an area of high salt concentration. In a salt bath of water of 3% solution, the parasites, being simpler creatures than the fish, can have the fluids withdrawn from their bodies by this difference in salt concentration. The same laws of osmosis exist for the fish so care and continuous observation of the fish during this treatment is essential. Once the fish begins to lie over on its side in a similar manner to that which occurs when a fish is sedated, it should be removed from this salt bath and placed into another container to recuperate. A maximum of two minutes is advised for this treatment which can be repeated if necessary a short time later.

An improvement in the disposition of a fish after this treatment can suggest that parasites may be the problem.

In the wild, fish can often rid themselves of parasites by changing where they live in a lake. River fish can have parasites washed downstream where they can no longer infect them. However, in a closed pond system, the detection of a parasitic infection is best dealt with by the appropriate treatment. Always check water parameters first if fish behave in an unusual manner.

Spring variations in temperature can stress fish. They have evolved to expect quite stable temperatures, which change very slowly with the seasons. Large bodies of water resist temperature changes much better than small ponds.

Tips on using the microscope

A microscope can assist in making a precise initial diagnosis of the problem, and as you will appreciate from the following text, further microscope tests are preferable in order to apply follow up treatments which are necessary with some parasites, such that the reproductive cycle of the parasite is broken.

Preparation of a microscope slide

One of the main reasons for failure to detect parasites on a skin scrape is incorrect preparation of the slide sample. The following tips should help in taking a sample of mucus from the fish and preparing the slide. Large quantities of mucus are not needed and should be avoided or mixed with clean water to make them less dense.

Samples of mucus from the skin

Net the fish and gently use the glass slide to remove a small amount of mucus from the surface of the skin. The term “skin scrape” is misleading as you are only taking a small sample of mucus which covers the skin. Do not “scrape” the glass slide over the skin. A plastic credit card may be used if you doubt your ability to safely use a glass slide.

Add a small amount of water to the mucus sample on the microscope slide and cover it with the cover slip. Gently press the cover slip onto the slide until the sample spreads outwards towards the cover slip edge.

Always begin searching a slide with the microscope at the lowest power setting. This is usually 30/50X magnification. If the slide has been prepared correctly as above you will be looking at what is best described as an aerial view of a coastline with perhaps several islands lying off this “coast”.

Any large parasites should be visible at this magnification. Typically, mature forms of “Whitespot” and gyrodactylus (skin fluke) would be visible.

A further search of the slide at a higher magnification of 100X will reduce the amount of mucus sample visible through the microscope, as it appears to bring the sample closer to view.

Further explanations are given on identification as the various common parasites are discussed. It should be said that the major problem for anyone learning to use a microscope is what to ignore as “normal”. Later explanations and photographs taken through the microscope should help with firm identification of individual parasites.

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