Symptoms of Ichthyo
also called white spot diseases or spot diseases
external symptoms
- white spots on the fins
- white dots on the skin
- mucous membrane peels off.
Behave
- Fish scrub themselves.
- Fish become lethargic.
- Fish breathe heavily.
- Fish hide.
- Fish lose their appetite.
Photos of fish with Ichthyo
Photo: Mario
Ornamental tetra with a heavy infestation of white spot disease. The fins show signs of bacterial infection, probably fin rot.
Photo: Marion Philipp-Bogg
Catfish with severe Ichthyo infestation
Photos: Dirk Neidhardt
Butterfly cichlid with ichthyo
Photo: Jörg / Shaky
Yssichromis piceata Females with slight Ichthyo infestation
Photos: David Philip
Catfish with severe Ichthyo infestation
Photos: Hankie
Catfish with a slight Ichthyo infestation
Photos: Lars Slowak
Tetraodon pustulatus (blowfish) with ichthyo and fungal eye
Photo: Nils Grothaus
Red neon with heavy ichthyo infestation
Photo: Puntius (Forum)
Red mullet with Ichthyo
© Stefan Diaz Torres Photo: Jutta / juku © Stefan Diaz Torres
Cherry spotted tetra with heavy infestation by Ichthyo
Photos: Mathias Jetzer
Neon tetra and platy with a slight ichthyo infestation
Photo: Anne Kroll
Swordtail female with Ichthyo.
Photos: Dennis Roller
neon tetra and fighting fish with Ichthyo.
Photo: Emil Zaczek
Butterfly cichlids with Ichthyo.
Causes of Ichthyo
White spot disease is caused by the skin parasite Ichthyophthirius multifiliis. It is therefore often simply called Ichthyo. In German-speaking countries, the term semolina grain disease is also used. The pathogen goes through various stages of development, which must be taken into account during treatment.
First, the parasite, called a trophont or trophozoite at this stage, nests in the skin of the fish. Only at this stage does the pathogen eat. The trophont has no mouth, it secretes a substance that dissolves the neighboring fish cells and absorbs their contents. This substance also causes the outermost skin cells of the fish to thicken. This essentially causes the fish’s own immune response to protect the pathogen from external remedies by the fish’s mucus secretion and skin cells.
The trophont constantly rotates within this protective shell and increases in size up to 50 times its initial size until it finally becomes visible as a small white dot or nodule between 0.2 and 1 mm in size. Balls can be seen under a microscope that rotate quickly and have a fringe of ciliated hairs. Inside you can see a U-shaped nucleus lying in the dark cell mass. Depending on the temperature, he is adult after a few days or weeks. He sheds his eyelashes and develops a thickened, gelatinous outer covering. It migrates into the slime layer of the fish and eventually falls off the fish.
The tomont swims freely in the water for two to six hours and eventually attaches itself to plants, the substrate, mulm particles and other objects. Bright spots are preferred to dark spots. In the short period of free swimming, the pathogen is sensitive to medication. Once attached, it forms a cyst-like capsule around itself. Protected only by a thin gelatinous layer, the cysts die as they dry out. Catch nets and other items should therefore be dried completely after being used in an aquarium where Ichthyo has emerged.
The parasite can divide into up to 1024, according to other sources up to 2000, possibly even up to 4000 cells in this capsule. These cells are called tomites. Depending on the temperature, they leave the capsule within hours or days, grow longer, quickly develop eyelashes that finally cover the entire pathogen and, as so-called therontes or swarmers, actively search for fish that they can infest. The swarmers may also continue to multiply outside of the capsule.
The hawk moths are good swimmers due to many lashes. They implant themselves as trophons in the skin by boring through the epidermis (outer layers of skin) with the help of a gland and with twisting movements and nesting between the epidermis and inner layers of skin. From that point on they are called Trophont and the cycle starts over. If the swarmers don’t find any fish, they die off after about 48 hours at 24° to 26°. Apart from the brief phase as a free-swimming Tomonte, only the Schraeder are sensitive to medication.
If an infested fish dies, all Trophonte leave the fish within one to four hours, regardless of their size and even if they are not yet fully grown. They encapsulate and begin to divide.
In a warm water aquarium, the complete life cycle takes about 3 to 7 days. From the life cycle follows that Ichthyo can break out in the aquarium for various reasons. Pathogens can get into the aquarium with new fish or plants, but the disease can also be passed on unnoticed for a while by a previously infected fish. Newly nested trophons are too small to be seen with the naked eye. In addition, in the early stages of the disease, the gills are often affected, where the pathogens remain undetected. Heavily infected small fish may therefore be too weak to save by the time the first visible dots are detected.
In this way, ichthyo pathogens are constantly present in many aquariums. With good husbandry conditions and healthy fish, the immune system of the fish prevents the excessive proliferation of the pathogens. In poor housing conditions or other stress factors, the immune system is weakened, the pathogens can multiply massively and Ichthyo breaks out.
Fish that have survived an infestation with Ichthyo produce more mucus. This means that no trophonts can nest in the skin over several cycles. However, they can attack the gills and continue to live there undetected. This explains the repeatedly reported outbreaks of ichthyo in aquariums that are supposedly free of ichthyo and into which no new animals, plants or objects have been introduced. Another possible explanation is that the hawkmoths, as documented in other species of ciliates, can exchange genetic material with each other, thereby greatly increasing their lifespan. Even if it is claimed again and again, there is no permanent stage in which the parasites can survive permanently and in the long term independently of the fish.
It has not yet been finally clarified why fish infected with Ichthyo die. It is possible that the oxygen supply through the gills is impaired by the thickening of the outermost cell layers. In addition, the surface of the gills deforms. In addition, the large number of parasites disturbs the oxygen supply. Eventually, the outer cell layers of the gills may detach. The fish constantly loses electrolytes, nutrients and fluids through the affected areas. It becomes increasingly difficult for the fish to breathe and regulate the water concentration in its body. In addition, fungi and bacteria can penetrate through the affected areas on the gills and skin.
Fish once infested with ichthyo can become immune to at least some degree. Apparently, an antibody develops in the fish’s mucus against proteins in the outer membrane of the hawkmoth. The antibody binds to the surface of the hawkmoth, preventing the hawkmoth from attaching to the fish. However, the swarmers are not killed.
Ichtyo can be confused with the less common Lymphocystis. Confusion with infestation with certain sporozoa species is also possible. If treatment for ichthyo is unsuccessful, these options should be considered.
Development time details
The development time for a complete cycle depends on the temperature. The higher the temperature, the faster the development occurs. Unfortunately, the information on websites and in the literature is not clear, since the different figures and times depend on the exact examination conditions. Because the respective conditions are not known in detail, the information can only be seen as an indication of the course of the disease and cannot be directly compared with one another. According to some sources, the hawk moths can survive in nature for several weeks. It is unclear whether this information can be transferred to tropical fish in the aquarium, whether different «ichthyo species» are involved, whether maximum values and average values are assumed, or what else explains the different information. However, this may explain reports about particularly protracted courses of the disease.
According to some information, the pathogen grows in the skin at 27° for about 5 days, according to other information without temperature information, 10 to 20 days, and then falls off. Up to 1024 swarmers form in the capsule within approx. 20 hours. According to other information up to 2000 or even 4000 swarmers develop. These live for about 48 hours at 24° to 26°, about 55 hours at 20° and can infest fish during this time. There is also information that the swarmers survive up to 4 days. With such statements, the aforementioned exchange of genetic material may play a role.
According to other information, the complete life cycle lasts 48 hours at 24° to 26° and 3 to 4 days at 21°. At 10° the cycle lasts at least 5 weeks.
There are different strains of Ichthyo that are differently contagious and have different sensitivities to drugs. In the meantime, ichtyho strains have been found that can withstand temperatures above 32°, which many fish species can no longer tolerate. In one strain, or a pathogen very closely related to Ichthyo, the tomonts no longer exited the fish but remained beneath the epidermis, where they developed and released the hawk moths. In such cases, one sees multiple cells of similar size very close together…