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[size=9]Viral infections

Carp Pox
Carp Pox is actually caused by a typical alpha-herpesvirus, and is probably better called Cyprinid Herpes Virus 1 (CHV-1). Affected fish show waxy growths on the body surface and fins which first make their appearance in late autumn, the number increasing over the winter and into the spring.
It is in the spring that it is often first noxiced by the Koi keeper, but if left alone, these growths will disappear of their own accord. This is because as the weather improves and temperatures increase, the fish mount an effective immune response, stopping viral production and resolving the wax-like lesions. However, the virus is able to survive in the fish from year to year, dormant in the trigeminal nerve and so repeated bouts will occur. Of no great problem to adult fish, it can be devastating in young fry which are not immuno-competant.
CHV-1 can be highly infectious, especially at high stocking densities; external parasites may also be important in spreading the disease.
Spring Viraemia of Carp
Although there have been outbreaks of SVC in the UK, we are considered fi-ee of the disease. SVC is notifiable under the Diseases of the Fish Act 1937 (as amended). SVC presents in two main ways:
(a) Usually, the fish will appear bloated due to a build-up of coelomic fluid (ascites); blood spotting is evident and the fish are lethargic and uncoordinated.
(b) Alternatively, only the swimbladder is affected, showing marked inflammation and haemorrhages; no other organs are usually involved.
Known prediposing factors are low temperatures (viral replication is slowed down, but its ability to cause disease is not affected, so deaths can still occur) and rapidly fluctuating temperatures. At higher temperatures fish are able to mount a better immune response, so fatalities are fewer. Other factors, such as age of the fish and extemal parasites, are also important in determining the results of an outbreak.
SVC is not considersd to be in the UK at present.
Bacterial problems
Aeromonas/Pseudomonas infections
Aeromonas salmonicida is a pathogen in its own right, whereas Aeromonas hydrophila and Pseudomonas species are secondary, opportunist invaders. Aeromonas and Pseudomonas bacteria are common inhabitants of freshwater habitats, and are also present naturally, both on fish, and as part of their flora.
Low temperatures, or rapidly oscillating temperatures, have been associated with an increase in bacterial numbers on the gills, skin and in the intestines of carp. As the temperature in spring continues to warm up, the immune system becomes more proficient. Unfortunately, bacterial replication also increases, as does their abiliry to cause disease.
Infections may present as aeveral different syndromes:
(a) Sudden death. This is what it says. No external signs may be seen. The fish immune system has been completely overwhelmed..g
(b) Haemorrhagic Septicaemia. Affected fish will show haemorrhages on the body surfaces and venous "streaking" of the fins. The fish show typical signs of illness, with fins pressed tight against the body, appetite depression and general lethargy.
(c) Ulcer Disease.The commonest cause of presentation of koi to the vet! Single or multiple erosions. classically, on the flanks, but may affect any part of the body. If the ulcers are large enough, death results from a disruption of osmoregulation and possibly loss of ions especially K+.
Cytophaga-like bacteria
Peduncle Disease / Coldwater Disease is a slowly progressive disease caused primarilv by Cytophaga psychrophila. This disease is considered a secondary infection, occurring when the fish are otherwise stressed. Ideal temperatures for growth are in the range of -1 to 10°C (39 to SO°F) - precisely the range in which the Koi immune system is least able to handle the infection. The disease often starts as a fin rot, but then progresses down to the base of the fin to form a large alcer, which may go so deep as to expose the vertebrae.
Bacterial Gill Disease is a complex disorder, probably resulting from a combination of adverse environmental condition and the presence of bacteria of varying disease-causing abiliry.
BGD manifests itself by the fish becoming lethargic and off their food, plus an increased respiratory rate, coughing, flared gill covers and mucus strings trailing from the gills. Outbreaks in carp have been known to occur at temperatures as low as 5°C (41 °F).
Chlamidia-like organisms
Epitheliocystis is caused by intracellular, bacteria-like pathogens which have yet to be definitively classified. They seem to infect the mucus-secreting cells in the gills and skin of carp, where transparent or whitish cysts are formed. In large numbers they cause damage to the gills, and respiratory distress partially due to excessive mucus production. In carp, especially, there is a proliferative reaction, which can be associated with low temperatures, in which the surrounding tissues form a signicant fleshy mass. In appearance, Epitheliocystis can be difficult to distinguish from the viral infection Lymphocystis. However, Lymphocystis does not infect carp!
Fungal Disease
Saprolegnia needs no introduction: this is the classic freshwater disease which afflicts most freshwater fish. Typically, this presents as a cottonwool-like growth, and can affect any part of the fish.
Fungal spores are present in the environment, and infections are usually secondary to other infections, trauma or stress. Low temperatures favour growth of the fungus because of the associated immune suppression.
Protozoal Parasites
Hoferellus cyprini
H. cyprini is a kidney parasite of carp which become infected after eating infested tubificid worms. Badly infected fish are off' colour, stop feeding and progressively lose their balance until they die after around 7 to 14 days.H. cyprini is mentioned here because spring is the time when carrier fish shed spores into the pond water in their urine.
Trypanoplasma species
Trypanoplasms are parasites found in the blood. Those of potential importance to Koi are T. cyprini, T. borreli and T. tincae.
Fortunately for the UK Koi population, this infection needs to be transmitted by leeches, including Piscicola geometra, and so only those stocks living in or brought in from natural waters will be at real risk. Affected fish are anorexic, listless, show weight loss and are anaemic. Blood clotting is reduced.
Times of greatest risk are over winter, when the Koi immune system is depressed, and late spring, when there are large numbers of leeches around.
Ichtyobodo necator
Formerly called Costia necatrix, this ectoparasite is able to survive temperatures down to 2°C (35.6°F). Even at this low temperature, massive infestations of hibernating carp have been described.
The first obvious signs are dull areas on the skin due to secondary mucus production in response to the parasite. Badly affected fish lose their appetite, swim with their fins clamped and may scrape against objects. The skin becomes reddened, then haemorrhagic, while the gills are pale and covered in thick mucus. Saprolegnia (Fungus) is a common secondary invader.
Chilodonella
These motile protozoa graze on epithelial (lining) cells of the gills and skin. The irritation caused resuits in excessive mucus production, as well as clamped fins, respiratory distress and depression.
Temperatures of 5-10°C (41-50°F) seem to be close to the optinmum for C. cyrini, giving them a significant headstart on the Koi immune system in spring.
DON'T FORGET!
Most pathogens of Koi are normally found in small numbers, both on the fish and in the environment. This constant low challenge helps to keep the immune system of the fish primed, as a kind of natural vaccination.
Ichthyophthirius
The White Spot Disease parasite has a complicated life cycle, with stages both on the fish and in the environment. The life cycle of Icthyophthirius multifiliis is modulated by the environmental temperature. At 24-26°C (75-79°F), it is completed in around four days, whereas at 5°C (c44.5°F), it takes 35-40 days.
Therefore, during the winter months, the replicaton of the parasite is slowed down, but not arrested, giving it a numerical advantage as temperatures rise in the spring. However, Koi are able to mount a good immune response, especially at temperatures greater than ~12°C (c53.5°F), so that healthy fish will eventually shake off the infestation.
Koi stressed by severe overwintering conditions or other factors may not be so fortunate, with the associated immune suppression allowing large numbers of Ichthyophthirius cysts (which are the white spots) to establish. These can cause severe damage to the gills and skin, and also allow secondary infections to establish.
Epistylis
Also known as Hereropolaria, the Epistylis protozan is, basically, a commensal, that is to say, that it uses the fish purely as a surface on which to attach itself. Given conditions stressful to the host fish, such as lowered winter and spring temperatures, and high levels of organic matter in the water, Epystilis can increase in numbers, forming whitish fuzzy patches, which may progress to form ulcers in the skin. Secondary infection now occurs, with fish losses resulting from classic Bacterial Septicaemia. An attempt should be made to distinguish Epistylis from Saprolegnia (Fungus), as the two conditions can appear similar; this is best achieved with a basic light microscope.
Molluscs
In late spring, Koi kept in waters containing freshwater mussels may find themselves temporary hosts to glocchidia', the parasitic immature stage of these mussels. Generally little lasting harm is done, although the glocchidia may prove an irritation. There is a slight risk of secondary infection at the sites of attachment once the glocchidia leave their host.
Non-Infective Factors and Disorders
Temperature
First of all the ambient temperature affects not only the koi, but also the filter bacteria. Because of this, monitoring of water qualiy is vitally important - check levels of ammonia and nitrite particularly to makc sure that your biological filration is keeping pace with vour Koi.
pH
Check the pH as, although your concrete pond may be sealed, the concrete and cement used around the pond edge may not be, and the rain run-off from these areas into the pond may be causing the pH to rise.
Unwelcome arrivals
Many areas experience floods, and I would ask you not only to worry about what has escaped from your pond, but also what may have been washed into it!
Lightning
The uncertain spring weather can also bring problems of another kind - lightning strike has recently been put forward as an explanation for a sudden outbreak of broken backs in Koi in a pool, the supercharge of electriciry in the viciniry of the pool causing powerful contractions of the muscles along the spinal column, suffciently strong to fractuse some vertebrae!
Egg-binding
A bad spring can lead on to problems further on in the year. A classic example of this is egg-binding. Development of the ovaries and the eggs inside them is temperature-dependent prior to ovulation and spawning. In other words, there needs to be a certain number of days at a sufficiently high temperature for correct ovarian maturation.
If there is a poor spring, then the ovaries may not develop sufficiently to allow normal spawning to take place, giving a build-up of immature eggs. This problem is worsened by the fact that egg development is not synchronised, so that eggs are continuously produced (given ideal conditions, Koi will spawn several
times during the breeding season). These eggs can eventually be reabsorbed, but it can take up to two years if conditions are not favourable. Egg-binding in Koi is probably not fatal in itself, but it is an extra stress upon these fish, making them more susceptible to other disorders.
SUMERTIME PROBLEMS
Koi like it warm; they are most definitely not `cold'-water fish. In fact, happy Koi have a preferred body temperature of around 18-25°C (c64-77°F). Therefore, during summer, their whole metabolism is working at its optimum, food intake and digestion are at their most efficient and their immune systems are primed for maximal response. Yes, summertime is a good time to be a Koi ... usually.
Unfortunately, every silver lining has a cloud, and summer brings with it its own set of problems.
Environmental problems
What distinguishes summer from winter are, mainly, two factors: higher temperatures and more sunshine, both of which are important triggers to plant growth.
Algal blooms can therefore become problematic, and not just from an aesthetic point of view. Certain suspended algae, such as Chlorella secrete toxins which can interfere with breeding. A massive die-off of such algal blooms can produce a lot of decaying material in the pond, producing a serious oxygen depletion. Heavily planted ponds can also suffer from a lack of oxygen during the night, when the plants are no longer able to photosynthesise (which produces oxygen) but continue to respire which uses oxygen .
Carp are able to survive in water with poor oxygen levels by a combination of gulping in atmospheric air at the surface, and using certain anaerobic (non-oxygenrequiring) metabolic pathways, but it is still very stressful for them. During the night, not only are the plants using up oxygen, but they are also releasing carbon dioxide as a byproduct of respiration (as do fish). This carbon dioxide is very water-soluble, forming the acidic carbonic acidic. Therefore during the day, as the plants photosynthesise, carbon dioxide and even bicarbonate ions are removed from the water, which, in turn, causes an increase in pH, reaching a peak shortly before sundown.
Ponds with an overwhelming plant growth can therefore experience major pH swings over a 24-hour period, the pH rapidly falling at night, only to rise once more the following morning as the dissolved carbon dioxide is removed from solution by the plants photosynthesising again.
Ponds experiencing extreme algal blooms may be subject to super-saturation of the water with oxygen during the daylight hours. Fish in such ponds will often show signs of Gas Bubble Disease, with bubbles of oxygen forming in the blood vessels of the skin, fins and behind the eyes.
Sunburn
Koi swimming close to the surface, in clear water with no cover, may suffer from sunburn. This should be suspected if there is a lesion on the dorsal aspect (back) only, possibly including the dorsal fin. White areas, lacking the protection of pigmentation, may be particularly affected.
Herbicides and pesticides
All these compounds should be regarded as poisonous to fish and have no place in or around a water garden. For example, a random gust of wind may blow a mist of the chemical over your pool surface; or rainwater may wash it into the pond; or dead or dying insects may drop on to the water surface, where they are greedily consumed by your beloved Ogon ...
Medications
Formalin , a common ingredient of proprietary ectoparasitic preparations, lowers the levels of oxygen in the water, as well as being toxic to gill tissue. Combine this with warm water, with its reduced oxygen-holding capacity, and there could be trouble.
Malachite Green is more toxic at temperatures greater than 21°C (70°F), injuring the gills and blocking digestive enzymes.
Spawning
Not a disease, nor a disorder, of course, but a very frantic, physical and potentially traumatic event, which leaves the fish exhausteti, stressed, often damaged and susceptible to secondary infections.
Fungal diseases
Branchiomycosis
Branchiomycosis sanguinis infections are usually referred to as Gill Rot, because this fungus invades the gill tissue. Affected fish gasp at the surface, and appear weak and lethargic. Although the disease is often fatal, some fish will recover, regenerating their damaged gill tissue. Gill Rot is often associated with poor water quality, overcrowding, algal blooms and temperatures over 20°C (68°F).
Bacterial diseases
Lactobacillus piscicola, regarded as a normal commensal, may cause problems following spawning or rough handling. Often presents as a septicaemic condition, with internal haemorrhages, ascites (dropsy) and kidney granulomas.
Edwardsiella Septicaemia
E. tarda has been known to cause septicaemia in Koi. Infections are probably associated with poor water quality, high water temperatures and overcrowding.
Columnaris Disease
Outbreaks due to Flexibacter columnaris usually occur at temperatures over 15°C (59°F) in conditions stressful to Koi. External tissues are attacked first of all, with the fms and gills being prime targets. Erosions appear, often with a reddened rim. Eventually, the bacteria invade the bloodstream and there is a terminal spread to the internal organs.
Botulism
In deep earthen ponds with a heavy sediment layer, anaerobic conditions can develop, which at temperatures over 12 to 15°C (54-59°F) can favour the growth of Clostridium botulinum. Intoxication can occur following ingestion of the sediment or disturbance of it. Affected fish are initially uncoordinated, eventually becoming paralysed and dying.
External parasites
Trichodoniasis
Actually, there are three genera falling under this title - Trichodina, Trichodonella
and Triparciella. Infested fish produce excessive mucus and so have a greyish cast; later, skin erosions can form. The gills are also badly affected. In fact, in Koi, infestations may be limited to the gills alone. Affected fish will scratch, and may show laboured breathing or ixdlamed gills.
White Spot
Caused by Icthyophthirius multifiliis, the optimum temperature for reproduction is 24-26°C (75-79°F), with the entire life cycle being completed in four days at these temperattues.
Infections can build up rapidly, and mortalities can occur, especially if the gills are heavily parasitised. If they survive, Koi will develop good immunity to the disease.
Oodinium (Velvet) Disease~
O. pillularis can cause explosive outbreaks of disease, affected fish showing the characteristic greyish velvet-like film on the body surface.
Infected fish are itchy, constantly scratching, and may stop feeding. The gills may also be affected. O. pillularis contains chlorophyll and, under ideal lighting and temperatures (23 to 25°C - 73 to 77°F), can become infective within 2-3 days.
Argulus
Visible to the naked eye, this flattened crustacean parasite not only causes irritation to its host, but may also introduce secondary infections on its mouthparts. Egg production starts at 16°C (61°F), and, at ideal temperatures, the life cycle takes around 40 days.
Lernaea ~(Anchor Worm)
The head of this crustacean lies buried in the skin or gill tissue of the host, creating some irntation and a site for secondary infection. Mature females possess two egg sacs near the posterior of the body, producing a Y-shape. The lifecycle cannot be completed below 15°C (59°F).
Skin and Gill Flukes
Skin Flukes (Gyrodactylus) are live bearers, and can be the cause of skin irritation, with areas of increased mucus production. Occasionally, the gills are affected. More usually it is the Gill Flukes (Dactylogyrus) which cause problems with these organs, where they can be very destructive. Dactylogyrids are egglayers, with their life cycle shortened to a few days at 22-24°C (c72-75°F).
Ergasilus (Gill Maggots)
These copepod crustaceans are found usually attached to the gills, where the females with egg sacs are readily apparent. Gill damage can be severe, and may provide a source for secondary infection.
Internal parasites
Tapeworms
The tapeworms, Bothriocephalus and Khawia are found as adults in carp, with intermediate stages occurring in copepods (Bothriocephalus) and in tubificid worms (Khawia). Peak infection time for Bothriocephalus is mid-summer, whereas Khawia has a peak in late spring, falling in midsummer, then increasing from mid-July onwards. Unlikely to be a problem in adult Koi, both parasites can be devastating in young fish.
Blood parasites
Trypanosoma danilewskyi is a haemoparasite that is transmitted by the fish leech, Piscicola geometra. These parasites are really only a threat to debilitated fish. Affected fish are lethargic, with pale gills due to anaemia.
Sanguinicola inermis are digenetic trematodes (flukes) which live as adults in the major blood vessels of carp. The fish are infected by eating the intermediate hosts - aquatic snails. The eggs lodge in the gill vessels, where they hatch, damaging the gills and causing haemorrhage and extensive damage.
The above is just a sample of potential problems that can afflict Koi during the summer. The list could go on, with filter breakdowns, stress through travelling to shows and so on, all of which attain progressively greater signi ficance as summer wears on and autumn begins to loom.
BROODSTOCK & FRY
What is often overlooked is the preparation of broodstock. A thorough physical examination early in the season is important, taking care to check for any signs of ulceration, or parasites. Please remember to check underneach the fish, as lesions on the belly and anal fin can easily be overlooked. Correct feeding is important, as both ******es require extra protein for normal ovarian/testicular growth and function. Fats are also important, with significant reserves being laid down in the liver. These are utilised for energy during spawning and, in females, are needed for egg production. Therefore, diets with at least 8% lipids (fats) and 35-40% highqualiry protein should be provided. Failure to provide this may result in broodfish with reduced spawning vigour, reduced fertiliry and poor hatching.
Care of eggs & fry
Once released into the water, a Koi egg must be fertilised within 30-60 seconds (sperm remain viable for 1-2 minutes). Often, up to 40% of a spawning can be infertile. To try to reduce this, use at least two males to each female during spawning.
Following spawning, the eggs absorb water and swell, in a process called hardening. This is achieved by osmosis, water entering the relatively concentrated egg, from the dilute surrounding medium.
In waters which are excessively hard, with high levels of dissolved salts (such as certain spring waters), the difference in the levels of dissolved substances in the egg, compared with the surrounding water, may not be sufficient to induce osmosis and, hence, normal hardening.
Other causes of egg mortaliry and low hatchability include low oxygen levels, incorrect water temperature (fatal below around 16°C-61°F; above 25°C - 77°F - stimulates development but may produced weakened and deformed fry; over 30°C - 86°F - usually rapidly fatal. Rapid temperature changes will also cause embryonic death). Bacterial and fungal diseases can also cause serious die-offs of eggs and newly hatched fry.
After around two to six days (depending upon the ambient water temperature) the fiy hatch out. At this stage, they show marked light avoidance, seeking darkened areas in which to lie to absorb their yolk sac.
After 48 to 72 hours, fry development has progressed to the stage where they can become free-swimming. Following a quick dash to the surface to take in a guip of atmospheric air which is forced into the swimbladder, the fry alter their behaviour and seek out light, which usually draws them towards the highest densities of their food - infusoria.
Excessive levels of illumination or inadequate provision of shaded areas in the first two to three days can be stressful to fry, possibly opening the way to secondary infections. Very high or low temperatures are also stressful and, if uncorrected, may cause fatalities. This is also true of rapid temperature fluctuations. Further, growing on fry at too high a temperature can cause a loss in colour.
Following hatching, the oxygen requirements of the fry increase dramatically and, again, as the fry become free-swimming. Factors which further exacerbate this demand are high temperatures, high stocking densities, and overfeeding.
Poor water quality can also cause a loss of fry, especially high ammonia and nitrite levels. Some poor waters may have a thick, proteinaceous film at the surface, making it difficult for the fry to take in air into their swimbladder.
Gross overcrowding of the fry will lead to stunting. Koi closest to the original wild carp can grow at a prodigious rate, often out-competing their brothers and sisters for food, and if the size differential is too great, then cannibalism may result.
While on the subject of food, growth of the fry can also be reduced by feeding insufficient food, or poor-qualiry foods lacking in essential amino acids such as arginine and valine
Young fry do not possess a fully functioning immune system and this, combined with a rather delicate constitution, mea.ns that they are susceptible to a wide ra.nge of diseases. Many bacterial and fungal diseases can attack these young Koi.
Some notable parasitic infections include:
Icthyobodo (Costia) necator, which at:tacks the eggs and subsequently any carp fry which hatch. Overcrowding and high temperatures can cause explosive increases in Icthyobodo, resulting in mass fry mortaliry.
Sphaerosphora renicola. Uncommon in the UK, this myxosporean parasite is the cause of Swimbladder Inflammation (SBn in carp fry which can present as balance problems, inappetance (loss of appetite); at high temperatures (25 to 30°C - 77 to 86°F) the signs of SBI increase, with associated mortaliry.
Should the carp survive to the following year, they may then show vague signs, including anaemia (pale gills) and kidney enlargement. Secondary bacterial infections of the swimbladder are common, with one or both chambers filling with pus-like material, and with
gross thickening of the swimbladder wall.
Bothriocephalus. As the fiy grow, they change their feeding habits to include small crustacea, including Daphnia and copepods. This can expose them to certain worm infestations, such as Bothriocephalus, which uses a copepod as an intermediate host.
In a pond situation, or if one is using live food, a watch should be made for the presence of predators, such as the voracious dragonfly larvae, or the anemone-like Hydra.
NON-SEASONAI PROBLEMS
Dermocystidium koi
This posesses characteristics of both fungi and protozoa, although it is usuallt regarded as a fungus. It causes cysts in the muscles and skin. The life cycle is unknown, and although there is no recognised treatment, it rarely causes problems. Consider surgical removal if appropriate.
Sporozoon porasites
This group of parasites includes a number of species pathogenic to Koi. Included are Shaerospora renicola (see above), Chloromyxum cyrini and C. koi, which infect the gallbladder, Myxosoma dujardini and M. encephalina. The first of the Myxosomas causes yellow-white cysts in the gills, leading to breathing diffculties and death; the second infects the blood vessels of the brain.
Henneguya sp. manifests as cysts in a variery of organs, especially the gills and skin, while Eimeria sp. can cause severe enteritis (gastric disorders).
Fish tuberculosis
Classically, this disease is caused by infections with either Mycobacterium marinum or M. fortuitum (although others may be involved). This is a long term, debilitative disease which can present in a variery of ways, depending upon which organ(s) is (are) affected. Common presentations include longterm weight loss, or spinal curvarure (due to collapse of infected back bones). Potential zoonosis.
Tumours
Koi are potentially very long-lived and, as in all animals, tumours can be found in older specimens. In addition, longterm exposure to water pollutants can induce tumor formation.
Fatty Liver Disease
In the wild, carp spend a large part of the day foraging for food. This is partially because they lack a stomach, and so are unable to store one large meal to digest at leisure, and partially because much of
their natural diet is nutritionally poor, significant quantities need to be ingested. In captivity, Koi are usually fed hig quality, energy-rich diets. Any exce foods not used to provide energy for swimming, egg production, metabolis and the like will be converteded to fats and stored, particularly in the liver.
Over the years, these stores can become so great that normal liver function is disrupted. Unfortunately, fatty liver is usually diagnosed at post mortem.
Force feeding energy-rich diets to accelerate the growth of young Koi can bring about a similar siruation. Low levels dietary vitamin E will fail to prevent this fat turning rancid over time, which is a further co~ plication. Advanced cases of vitamin E deficiency result in Sekoke Disease (appetite loss, poor growth, muscle wastage and death), which will not be seen if one feeds a good-qualiry brand of food.
WINTER WIND-DOWN
Autumn is just around the corner, and with the shortening days and lower average temperatures, Koi begin to undergo a series of physiological changes that will help them to survive through the winter. These changes involve alterations to the muscle, nervous system, blood and metabolic pathways. Genes in the liver are triggered which increase the production of non-esterified fats incorporated into myelin sheaths and other cell membranes, because they are less likely to solidify at lower temperatures. Another important consequence of lowered temperatures is the suppression of the fishes' immune system, such that fish are less able to deal with infections (although, fortunately, the disease processes of most infections are a slowed down).
Other Factors :
Vegetation
Vegetation in the water comes from two sources: in and around the pond. Dealing with aquatic vegetation first, autumn is time to cut back water lillies and other plants as the leaves start to die. Lea vesfrom surrounding deciduous trees can be a problem and are best dealt wi:h by covering the pond with a net, or using a skimmer.
In both cases, if vegetation is left decompose, then water qualiry, as is often repeated, can suffer badly, stressing Koi and putting them at a disadvantage.
Filters
Filters can be cleaned out at this time year, as there is plenry of time for the beneficial bacteria to recolonise the media before winter temperatures slow down the bacterial proliferation . With multi-chambered filters, clean out one chamber per week. If you have the facility, change the pond intake from the bottom drains to one part way up the water column. This tends to preserve a static, deeper layer of water which, thanks to the unusual properties of water, will remain at around 4°C (39°F) irrespective of the weather above the surface, providing an ideal place to sit out the coldest months.
Ponds which do not have this faciliry, or which are not deep enough, will subject the Koi to a constant water flow, forcing them to swim, thus using up valuable energy reserves, and exposing them to water being continuously cooled by its journey through the filtration unit. Reducing the water flow will help, but this should not be stopped altogether, as the bacterial colonies, necessary for the filter's function, will be starved of oxygen.
Examinations
If possible it is worthwhile gently catching each and every fish in early autumn, giving them a quick examination to check for small ulcers, external parasites and the like. Any obvious lesions or infections should be dealt with at this time, if necessary isolating individuals in a heated treatment vat to encourage rapid healing before the fish are exposed to the rigours of winter.
Feeding
As the average water temperature starts to drop, our thoughts turn towards the vexing subject of feeding. Koi see out the coldest months of the year in a state of apparent dormancy, living off stored deposits of fat and protein. It is worth noting that a temperature drop (from 20 to 10°C - 68 to SO°F) will reduce protein digestibility, and since, during autumn, we are not trying to encourage growth, we can see that, apart from it being wasteful to feed excessive (and expensive) levels of protein at this time, reduced digestibiliry can also lead to a bacterial overgrowth on protein left in the gut.
Immunity
As daylength shortens and temperatures fall, the Koi immune system becomes less effective, and one may see the first signs of Carp Pox, or a reoccurence of bacterial septicaemias and ulcers. These latter conditions should be attended to immediately.
Dormancy
During the winter, Koi appear to enter a state of hibernation, characterised by reduced activiry, a reduced response to external stimuli and a low respiration rate. It is not a true hibernation though, as the fish can still respond to stimuli, and their sluggish attempts to swim away in these circumstances may be more a reflection of their inability to react at these low temperatures, rather than perceive the stimulus.
Therefore, breaking any ice that form at the surface with a hammer is not a good idea, as shock waves will be sent through the water, where they will be sensed by the Kois' lateral line - a stress that may be too much in their weakened state. A floating heater is a much better way of keeping an area of pool surface clear.
Reduced metabolic rate means a sluggish circulation, which, in the longer finned socalled Butterfly Koi, may lead to congestion in the fins, predisposing them to damage and disease. At these very low
temperatures, the immune to be virtually ineffective. Fortunately, the majoriry of pathogens are also depressed by the low temperatures, so their abiliry to produce disease is reduced, although over a prolonged period of time, they may still build up to problem levels.
TREATMENT OF DISEASES/DISORDERS DISCUSSED
Carp Pox /CHV-1 Will usually disappear of its own accord, only to return next year.
Spring Viraemia of Carp In theory, one would provide supportive treatment such as covering antibioics. However, in the UK, SVC is notifiable, and affected fish stocks may be required to be euthanased.
Aeromonas/Pseudomonas Antibiotics by injection, in food or in a special treatment bath - NEVER directly into the pond water. Which antibiotic will depend upon Iaboratory sensitivity tests. Large ulcers may require cleaning and topical treatment, often with the fish anaesthetised.
Cytophaga-l ike bacteria As for AeromonaslPseudomonas.
Bacterial Gill Disease As for AeromonaslPseudomonas. A salt water bath (10- 20g/I) for 1-2 minutes will help, as will chloramine-T at l0mg/I for one hour.
Epitheliocystis Not much information available. May respond to chloramphenicol .
Saprolegnia (Fungus) Gently remove as much of the fungus as possible and swab with a 10% solution of povidone-iodine. Malachite Green Bath at 2mg/l for 30 minutes, often once only- watch out for respiratory distress.
Hoferellus cyprini No known treatment. Attempt to restrict access of Koi to tubificid worms (impossible?)
Trypanoplasma Best controlled by elimination of leeches.
Ichthyobodo necator Use a proprietary treatment or glacial acetic acid dips at 8ml per gallon, for 30-45 seconds.
Chilodonella Formaldehyde at 25ppm, followed by a water change in 4 to 8 hours, or salt at 3g/I until symptoms stop.
Ichthyophihirius Use a proprietary White Spot Remedy.
Epistylis Salt at 22g/I for 30 minutes every 7 days for 3 weeks.
Glocchidia Will drop off of their own accord. Damaged skin may require attention as outlined above for ulcers.
Egg-binding Tricky- prime the fish with carp pituitary injections, and attempt manual spawning. Raise environmental temperature.
Algal Blooms All the problems associated with algal blooms can he avoided by installing ultra-violet units, and increasing the pool aeration. Increased aeration will even help to prevent oxygen super-saturation, associated with Gas Bubble Disease.
Sunburn Provide access to suitable cover.
Herbicides/Insecticides Avoid using these compounds around ponds. Due to the wide range of chemicals used, each with different effects, diagnosis is difficult and treatment rarely possible.
Medications Always rrrake sure that thc: water is well aerated, especially where products containing formalin are concerned.
Spawning traumas Clean up and treat as appropriate. Remember that the scales are embedded in the skin, so scale loss will produce a serious skin defect.
Branchiomycosis No known effective treatment. Concentrate on maintenance of optimurn water quality and stocking densities.
Lactobacillus Antibiotics (hased upon laboratory Edwardsiella Septicaemia sensitivity tests) by injection, in food or in a special treatrnent bath.
Columnaris Disease Columnaris may respond to benzalkonium chloride at 12ml/litre bath for one hour.
Botulism No known cure.
Trichodiniasis formalin-containing products should be effective, or give salt bath at 10-15g/litre for twenty rninutes.
White Spot Disease
Velvet Disease Use a proprietary rnedication.containing either formalin or copper.
Fish Lice (Argulus),and Anchor Worm (Lernaea) and Gill Maggots (Ergasilus) Can be problematic: remove individual Argulus and Lernaea, manually, with pond treatment for all three. with dichlorvos (licensed for use in salrnon)
Skin and Gill Flukes Praziquantel as a 3hour bath at l0rng/litre, or 400mg/100g food daily for 7 days. Advisable to repeat treatment affer 3 weeks for the egg--laying Dactylogyrids.
Tapeworms Praziquantal as above. Probably not feasible io control interrnediate hosts.
Trypanosomes Corrtrol by elirnination of leeches.
Sanguinicola inermis Oral praziquantel rnay be effective: (see above). Use of rnolluscides to control snail population.
Fungal lnfectlons of eggs Malachite Green, elther as a bath at 5.Omg/l for 60 minutes, or 0.2mg/I as a continuous bath.
Bacterlal Infectlons of eggs Antibiotic required (varies). Erythromycin at 50mg/l Is sbsorbed across the egg shell.
Fungal and bacterial infections of fry Where appropriate, treat as for adults.
Ichthyobodo necator Use proprietary medication.
Sphaerospora renlcola No recognised treatment.
Bothriocephalus Praziquantel at l0mgll for 3 hours at 22'C (72"F)
Predators such as Hydra and dragonfly larvae. In water treatments are fatal to fry, therefore attempt to control by screening all introduced plants. Control in large pond not feasible.
Dermocystidlum koi No recognised trestment. Consider surgical removal.
Tumours Surgical removsl may be possible if tumour small Euthenase fish if tumour interferes with normal functlon or behaviour
Sporozoan parasltes No effective treatments. Eimerias may respond to anticoccidial drugs or sulphonamides .
Flsh Tuberculosis Treatment problematic. This disease is infectious to man. Consider humane destruction of fish if diagnosed.[/size]

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