Fish disease

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Fish diseases are the subject of fish medicine and play a role in wild fish populations, in fish farming , aquaculture , aquaristics and the fishing industry .

The most important are infectious diseases including parasitoses , water-related damage and those caused by stress factors in the housing conditions. Injuries, hereditary diseases , deformities and tumors also occur in fish. Some infectious diseases can lead to mass losses in fish farming. They are then referred to as fish diseases and are subject to legal measures in accordance with the Animal Health Act , special legal ordinances and EU legal provisions. In Germany, four fish diseases are currently classified as notifiable animal diseases : infectious anemia in salmon , infectious haematopoietic necrosis and viral haemorrhagic septicemia in trout, as well as koi herpes virus infection in carp. The infectious pancreatic necrosis of salmonids (IPN) is a notifiable disease.

There is a complex interrelationship between the immune system, the pathogens and the living conditions, which ultimately determines the outbreak of infectious diseases. Different factors can trigger stress . This includes everything that disturbs fish and disturbs their rhythm of life, such as constant fiddling in the water, but also constant alternation of light-dark phases. Worsened water parameters, such as a lack or excess of oxygen , too high a content of ammonium , nitrite or CO 2 , as well as unfavorable pH values , wrong water temperature, lack of hiding places, wrong choice of species, or too strong current are also considered stress factors .

Stress weakens the immune system of the animals. As a result, they cannot maintain an immune imbalance with the mostly ubiquitous pathogens. Only then does an infection turn into a " disease " that breaks out .

Parasitic diseases

15-day-old larva of the Siamese fighting fish ( Betta splendens ) infected with Piscinoodinium

In principle, there are no fish without parasites - except immediately after medical treatment . They colonize the skin, gills, throat and internal organs such as the intestines, liver, kidneys, brain and, in some cases, the body cavities.

Parasitic diseases arise when these parasites spread through a weakening of the fish ("weakness parasite"). Weak parasites can then prevail when the body's own defenses of their hosts are weakened by poor housing conditions . Parasites are referred to as “diseases”, but they are not in the classical sense, but cause diseases in the host through their parasitic lifestyle. The extent to which the parasite influences its host is, depending on the case, largely determined by the host / parasite ratio, which, in addition to the disease-causing effect of the parasite, is determined by the immune system (resistance and immunity) of the host (fish) (ROMMEL et al. 2000) .

This knowledge is important for pond management, as carp ponds or commercial fish ponds, for example, generally offer extremely favorable conditions for the spread and transmission of parasites. This is formed on the one hand by stocking with only one fish species, which is equivalent to a monoculture , and on the other hand the stocking density increases in the course of fattening or breeding, so that both homoxic and heteroxic parasites are transmitted from host to host and epidemics develop be favored (ZANDER 1998).

White spot disease

Ichthyophthiriosis , known as "white spot disease" or "semolina", is caused by the ciliate Ichthyophthirius multifiliis and can occur completely unexpectedly in freshwater aquariums even with good water quality and varied food. The first signs are a reluctance to move and food refusal. After a few days, the eponymous white dots of the grown parasites appear in the skin. As a rule, all fish in a stock are affected. The most effective control is done with malachite green or methylene blue , but these are no longer permitted in food fish production . Alternative attempts at treatment with quicklime, Oxiper (sodium percarbonate) or chlorinated lime have so far been unsuccessful, the agents also have no drug approval and are therefore officially only allowed to be used to treat the water, but not the (table) fish (of any age).

Rotational sickness of fish

It goes back to an endoparasitic worm Myxobolus cerebralis , whose larvae (metacercariae) invade the brain and the organ of equilibrium and cause circular movement disorders. The parasite needs the mud tube worm - Tubifex tubifex - as an intermediate host. The disease cannot be treated, it can only be avoided by disinfecting the pond against Tubifex with quicklime or calcium cyanamide (CaCN 2 ).

Lump or lump disease

It is caused by the parasitic single cell Myxobolus pfeifferi ( Myxozoa ). The tube worm Tubifex tubifex is considered to be the vector . Affected fish species are mostly the barbel and the whitefish species. First, harder bumps form within the muscles, which gradually become softer and then break open outward like ulcers. It attacks the muscles and intestines of its host, where it forms cysts in which thousands of new spores are formed. If these cysts burst, the spores are distributed in the water to B. to be picked up again via the gills of other fish. Even dead fish can still spread Myxobolus pfeifferi using this method. There is currently no treatment for Myxobolus pfeifferi . Myxobolus luciopercae mainly affects carp, ruff, pikeperch and pike.

Swim cystitis in carp-like fish

It is caused by the parasite Sphaerospora renicola (Dykova et Lom 1982) and attacks the host's bloodstream and causes kidney disease. In the first stage, plasmodia collect in the sponge tissue of the heart muscle and migrate through the bloodstream into the swim bladder during their further development. There they reach a size of up to 30 µm (micrometers) and cause irreversible damage to the gas exchange between blood vessels and swim bladder lumen. The first signs are a thickening and a clearly yellowish to brown cloudiness of the swim bladder wall in the rear area of ​​the junction between the anterior and posterior chambers. At the same time, inflammation and necrosis of the eyes occurs later, with subsequent blindness of the fish.

Cyprinid diseases caused by flagellates

Mastigophora ( flagellates ) Cryptobia, Trypanoplasma and Trypanosoma spp.

Parasites living in the fish's bloodstream include flagellates of the genera Cryptobia (especially Cryptobia branchiales ) and Trypanoplasma . In Cyprinids is in Europe mostly Trypanoplasma borreli (syn. Laveran et Mesnil, 1902 Trypanoplasma cyprini Plehn, 1913 and Trypanoplasma carassii Kashovski, 1974) encountered. In contrast to the trypanosomes (e.g. Trypanosoma danilewskyi Laveran et Mesnil, 1904, Trypanosoma carassii Mitrophanow, 1883), the trypanoplasms have two flagella. Diseases caused by trypanosomes are symptom-free in most cases; kidney damage, ascites ( ascites ) and exophthalmos (bulging eyes) can only occur if the disease is more severe . The pathogenicity of numerous trypanoplasms depends strongly on the host species affected, with clear differences in the severity of symptoms even between closely related cyprinid species being observed (Schäperclaus 1990b).

The Hexamitiasis (hole disease) by Hexamita salmonis causes the Spironucleus disease by Spironucleus elegans .

Mycoses

Diseases caused by fungi are called mycoses. Among other things, fish include:

Bacterial diseases

Bacterial infections can be traced back to poor hygiene as well as organic pollution and overstocking. In the fish's home biotopes, an infection by bacteria occurs only in a few cases due to the prevailing milieu and the non-existent mass occurrence of the fish population in a very small area.

The most important bacterial diseases in fish farming are

  • Furunculosis by Aeromonas salmonicida ssp.salmonicida of the trout or the
  • Carp Erythrodermatitis (CE) in carp caused by another subspecies of Aeromonas salmonicida .
It was previously referred to as the "ulcer form of the infectious ascites" of the carp and was considered to be a form of ascites, which also includes today's spring viremia (SVC = Spring Viremia of Carp), which is caused by the carpio rhabdovirus .

Mouth or fin rot

White mouth disease is also known as mouth mold or mouth rot. In English-speaking countries one speaks of the cotton-wool disease. Another name is Saddleback Disease. The disease is common in trout farming. In the aquarium hobby, viviparous fish are preferred. It is a bacterial disease caused by the bacterium Flavobacterium psychrophilum . The previous name was Flexibacter columnaris , from which the name of the disease, Columnaris, is derived. As the German term for the disease suggests, white spots that look like mold tend to form in the mouth area, on the edges of the scales and on the fins. The infestation often spreads from the mouth or the fins over the whole body until the skin is affected by numerous white-gray ulcers. In the case of severe infestation, the fish lips are completely destroyed, the fins decompose until only the fin rays are left.

In the case of columnar infestation, a distinction is made between an acute and a chronic form. In the chronic form, the course of the disease is slow, the white areas slowly get larger before the infected fish die after a long period of time if left untreated. In the acute form, the white areas spread very quickly and the fish die within a very short time.

Viral diseases

There are various forms of farm fish that are host-specific;

Trout

carp

  • Spring viremia of carp (SVC or Spring viremia of Carp , formerly known as ascites) caused by Rhabdovirus carpio , and
  • Koi herpes virus infection (KHV), recently also significant and legally listed as a notifiable fish disease in normal carp.

Eels

Physically and chemically caused damage

Metabolic disorders due to unfavorable parameter combinations in the water:

  • Gill necrosis (KN) of the carp, destruction of the gills by ammonia self-poisoning in pond water with a high pH value (from around pH 9.0).
  • Similarly, a gill disease of trout, which is popular with a combination of scarce oxygen with little CO 2 occurs and the initial stage through much CO 2 disappears and / or a lot of oxygen, but without these measures, a positive feedback manner, to permanent necrosis escalates . Physiologically, it is an alkalosis , i.e. an excess pH of the blood, especially in the gill area.
  • The counterpart to this is acidosis (over-acidification of the blood), which occurs when the CO 2 and / or oxygen are permanently too high . The disease takes the form of nephrocalcinosis (calcification of the kidneys).

Consequences of oversaturation of the water with dissolved gases:

  • Gas bubble disease , especially due to technical water treatment (pumps, piped water supply, ventilation) in trout farms, an ubiquitous and often lossy “technopathy”.

The physico-chemical damage also includes sunburn , yolk coagulation, yolk blistering, and chemical burns caused by excess pH, as well as all kinds of poisoning.

Fungal diseases

Trout with fungal disease

The diseases caused by fungi are called mycoses .

Mycoses always occur as secondary infections. The fungi therefore attack the skin tissue that has previously been damaged by injuries or other diseases. Two-dimensional fungal infections occur very frequently after a gas bubble disease that affected the fish's scallops. Fungal diseases are only possible if the mucous membrane, which acts as the fish's “protective coat”, is damaged and thus offers a target for fungi to attack. The most common genus of fungus in fish is Saprolegnia , which is a water mold . A clear feature in the continued stage are cotton-ball-like growths on the skin. Non-treatment leads to the death of the animals. Fungal diseases are not infectious. Rather, the ubiquitous fungi use a weakening of the fish's defense system to colonize the body of the fish.

Over-the-counter anti-fungal drugs usually contain copper sulfate or copper chloride as active ingredients. These substances are deadly for invertebrates such as snails, crabs or shrimp, even in small doses, as well as for catfish and catfish-like species. Other species tolerate more. Iodine-free salt therapies are much more moderate in their effect and are much better tolerated by fish, provided that it is “only” a fungal disease. Malachite green , which is forbidden for use on edible fish, is successful in aquaristics .

Nutritional damage

Nutritional damage such as curvature of the spine, sunken bellies, pale colors, apathy and susceptibility to disease are the most common outcomes that result from improper nutrition. Not all fish are Omnivor (omnivores), herbivores (plant eaters), or Carnivore ( Carnivore ), but depending on the type, certainly very specialized in their diet. If the necessary consideration is not given to the special needs of the diet, deficiency symptoms occur in the long term, which then weaken the fish and make it susceptible to other diseases.

Refusal to feed (anorexia) in fish is not due to illness. Anorexia is always directly related to living conditions. A deterioration in the general water parameters (oxygen, ammonium / ammonia, nitrite, pH) is the most common cause.

Nutritional errors are the cause of the following symptoms:

  • Cachexia (emaciation)
  • Spawning degeneration and behavior
  • Lipoid liver degeneration : caused by one-sided or overfeeding of inferior food, which then leads to liver damage. Most common and undetected cause of fish mortality in the aquarium hobby.
  • Gastrointestinal inflammation
  • Deficiency disease (lack of protein or vitamins)
  • Nephrocalcinosis : It is a calcium deposit in the kidney tissue. Either caused by an already damaged kidney or by a disturbed calcium metabolism. This often leads to kidney failure in fish.
  • Steatosis (obesity)

Hereditary defects

Hereditary defects often occur in cultivated forms (goldfish, veil tails, guppies, etc.). Mating siblings or parent animals with the offspring inevitably leads to genetic damage. This can only be avoided if parent animals from different breeding lines are used. Hereditary damage can no longer be corrected even with optimal housing conditions and is passed on to the next generation.

prevention

Basically, depending on the species, an appropriate water environment must be ensured. Observing water hygiene is still the most important factor in protecting against the outbreak of various fish diseases. Quarantine is advisable before bringing them into old stocks. In quarantine conditions, possible infections should be treated better and the fish should be observed more closely. Quarantine is indispensable when it comes to farmed fish, since legal bases such as the Animal Health Act also play a role in the event of an outbreak of disease .

When choosing new ornamental fish for the home aquarium, you should watch the animals at the dealer for a while. The fish should move with agility and show no signs of indolence or apathy , and they should eat well. The color should also appear strong and of course none of the symptoms mentioned above should be recognizable. Responsible traders also have a quarantine facility in which sick fish are treated separately.

With some diseases, such as white spot disease , it is advisable to leave the animals in their traditional pelvis and treat this with special medicine. It is also advisable to increase the water temperature by several degrees for a few days and to ensure good ventilation, as this shortens the life cycle of the parasite and promotes the effectiveness of the remedy.

The most important preventive measures in the aquarium hobby , however, are strict adherence to the very best keeping conditions. This includes the observation and regulation of the water values, temperature and the like. Ä. or the correct feeding according to the needs. It is precisely here that mistakes are made. B. unsuitable or too much feed is served. This can weaken fish so that they become sick, or it can lead directly to gastrointestinal problems such as constipation, e.g. B. Uplinkers like Tropheus , Petrochromis or other Tropheini are very endangered.

The overstocking can lead to a high germ density, but also to poor water values. An inappropriate filter technology as well. Therefore, as well as the appropriate water change, care should be taken here.

Excellent water treatment guarantees less susceptible fish. This can be supported with oxidizers and, above all, UV-C lamps. The germ density is kept low. It is a fairy tale that the fish are “pampered” by it. Enough germs remain for conditioning. The fish remain vital and less susceptible to diseases.

Possible dangers for humans

Since you can come into contact with water again and again during fish care, the transmission of various pathogens to humans is possible, but mostly unlikely. Diseases that can be transmitted from animals to humans are called zoonoses . With the exception of a single worm disease z. B. still the fish tuberculosis transferable to humans. These infections cause so-called swimming pool or aquarium granuloma in humans.

literature

  • G. Bassleer: Illustrated atlas of fish diseases in freshwater aquariums . Naturbuch Verlag, Augsburg, 1996 ISBN 3-7888-0372-X
  • G. Bassleer: Fish diseases in salt water aquariums . Dähne Verlag, 2000 ISBN 3-921684-88-9
  • Wilhelm Schäperclaus, Hugo Kulow, Kurt Schreckenbach: Textbook of fish diseases . 5th edition, Akademie-Verlag 1990 ISBN 3-05-500190-7
  • Heinz-Hermann Reichenbach-Klinke: Diseases and damage to fish . 2., completely reworked. Edition - Stuttgart, Fischer 1980 ISBN 3-437-30300-7
  • Erwin Amlacher: Pocket book of fish diseases: Basics of fish pathology ; with 19 tab .; 6., revised. Ed. Jena and Stuttgart, Fischer, 1992 ISBN 3-334-00350-7
  • Ornamental fish health . ISBN 3-540-55535-8
  • Healthy fish . Aquarium Live, 03/2006

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