White Spot Disease ('Ich') - Ichthyophthirius multifilis (freshwater) & Cryptocaryon irritans (marine).
'Ich' is a very common protozoan disease of both marine and freshwater fish.
The organism is a small, round ciliated protozoan with a distinctive horse-shoe shaped nucleus that lives on the skin and gills of the fish where it produces lesions that take on the form of tiny (~1mm) white cystic nodules.
Clinical Signs The parasitic cysts are so large that they are visible to the naked eye.
Affected fish will look as though they have been sprinkled with sugar and will often demonstrate irritation; scratching and rubbing against the rocks and tank.
However, this may not always be present if only the "swarmer" stages are present.
Thickening of the skin epithelium and increased mucus production on the skin may occur, but these may only be appreciated microscopically.
The fins may also become ragged.
Since the gills are also exposed to the external aqueous environment, the organism will also parasitise the gills, causing increased mucus production as well as gill epithelial hyperplasia.
This leads to respiratory embarrassment and fish will present with increased respiratory rate and flared opercula.
In heavy infestations, fish will become lethargic and depressed, their respiratory rate slows down and becomes shallow.
Ulcers form when the encysted stages break out of the skin and the gills.
In heavy infections, mortality can be high which may be in part due to electrolyte loss (in freshwater fishes) or dehydration (marine fishes) through these ulcers.
In those that survive the initial insult, the ulcers would provide portals of entry for secondary infection with bacterial and fungal opportunists.
Transmission 'Ich' is a very common infection of fish in both freshwater and marine systems and, in low numbers, may produce little or no clinical signs.
It is important therefore to always look for other pathogens (bacteria, fungi, other protozoa etc.
) when presented with a sick fish with only a small burden of Ich, as this may be an incidental problem.
'Ich' replicates quickly and so a minor burden in one fish tank can rapidly become a serious burden to a tank full of fishes if left untreated.
Mature Ich parasites that have been feeding on the host eventually fall off the host to the bottom of the tank.
There they secrete protective cysts around themselves and begin to divide, producing many hundreds of swarmers (infective stages) which swim off in search of a host.
The transmission of 'ich' is facilitated by high stocking densities of fish.
Individual encysted stages on fish may go unnoticed by fish-owners and yet be a major source of infection to other fish.
Temperature also plays a big role in disease transmission with the lifecycle being completed more rapidly at higher temperatures (3-4 days at 21oC vs 5 weeks at 10oC).
This factor is particularly important when dealing with Cryptocaryon outbreaks as it is more temperature-governed than Ichthyophthirius.
Diagnosis Diagnosis is made by performing a skin or gill scraping in the region of one of the white lesions and by identification of the spherical ciliate organisms, with their characteristic slow spinning motion, in a fresh wet preparation.
Notice also that the parasites can be of various sizes, which is pathognomonic for "Ich" (other ciliated parasites are of uniform size and shape).
You may notice the horse-shoe shaped nucleus.
Treatment Formalin may be used, however, because it displaces dissolved oxygen, it is not recommended if fish exhibit severe respiratory embarrassment.
Malachite green + formalin combination is the most effective treatment since the mixture has a "synergistic effect" and a smaller concentration of each ingredient is used.
Dip treatments and osmotic challenges will only be effective against the non-encysted stages of the parasites.
Thus, this will need to be repeated every 2-3 days for 10 days.
Thermal challenge by raising the water temperature to at least 32oC for a few hours every 3 to 5 days (provided the water is well-aerated and that the fishes will tolerate it) is another method used.
The high temperature interferes with the reproduction of the parasites.
Since the organisms are obligate parasites, allowing the aquarium or pond to be left fish-free for at least 7 days at >20oC usually eliminates the white spot parasites.
It has been reported that some fishes that recover from the infection will develop immunity to the disease.
This article taken from Loh & Landos (2011) Fish Vetting Essentials, Richmond Loh Publishing, Perth.
'Ich' is a very common protozoan disease of both marine and freshwater fish.
The organism is a small, round ciliated protozoan with a distinctive horse-shoe shaped nucleus that lives on the skin and gills of the fish where it produces lesions that take on the form of tiny (~1mm) white cystic nodules.
Clinical Signs The parasitic cysts are so large that they are visible to the naked eye.
Affected fish will look as though they have been sprinkled with sugar and will often demonstrate irritation; scratching and rubbing against the rocks and tank.
However, this may not always be present if only the "swarmer" stages are present.
Thickening of the skin epithelium and increased mucus production on the skin may occur, but these may only be appreciated microscopically.
The fins may also become ragged.
Since the gills are also exposed to the external aqueous environment, the organism will also parasitise the gills, causing increased mucus production as well as gill epithelial hyperplasia.
This leads to respiratory embarrassment and fish will present with increased respiratory rate and flared opercula.
In heavy infestations, fish will become lethargic and depressed, their respiratory rate slows down and becomes shallow.
Ulcers form when the encysted stages break out of the skin and the gills.
In heavy infections, mortality can be high which may be in part due to electrolyte loss (in freshwater fishes) or dehydration (marine fishes) through these ulcers.
In those that survive the initial insult, the ulcers would provide portals of entry for secondary infection with bacterial and fungal opportunists.
Transmission 'Ich' is a very common infection of fish in both freshwater and marine systems and, in low numbers, may produce little or no clinical signs.
It is important therefore to always look for other pathogens (bacteria, fungi, other protozoa etc.
) when presented with a sick fish with only a small burden of Ich, as this may be an incidental problem.
'Ich' replicates quickly and so a minor burden in one fish tank can rapidly become a serious burden to a tank full of fishes if left untreated.
Mature Ich parasites that have been feeding on the host eventually fall off the host to the bottom of the tank.
There they secrete protective cysts around themselves and begin to divide, producing many hundreds of swarmers (infective stages) which swim off in search of a host.
The transmission of 'ich' is facilitated by high stocking densities of fish.
Individual encysted stages on fish may go unnoticed by fish-owners and yet be a major source of infection to other fish.
Temperature also plays a big role in disease transmission with the lifecycle being completed more rapidly at higher temperatures (3-4 days at 21oC vs 5 weeks at 10oC).
This factor is particularly important when dealing with Cryptocaryon outbreaks as it is more temperature-governed than Ichthyophthirius.
Diagnosis Diagnosis is made by performing a skin or gill scraping in the region of one of the white lesions and by identification of the spherical ciliate organisms, with their characteristic slow spinning motion, in a fresh wet preparation.
Notice also that the parasites can be of various sizes, which is pathognomonic for "Ich" (other ciliated parasites are of uniform size and shape).
You may notice the horse-shoe shaped nucleus.
Treatment Formalin may be used, however, because it displaces dissolved oxygen, it is not recommended if fish exhibit severe respiratory embarrassment.
Malachite green + formalin combination is the most effective treatment since the mixture has a "synergistic effect" and a smaller concentration of each ingredient is used.
Dip treatments and osmotic challenges will only be effective against the non-encysted stages of the parasites.
Thus, this will need to be repeated every 2-3 days for 10 days.
Thermal challenge by raising the water temperature to at least 32oC for a few hours every 3 to 5 days (provided the water is well-aerated and that the fishes will tolerate it) is another method used.
The high temperature interferes with the reproduction of the parasites.
Since the organisms are obligate parasites, allowing the aquarium or pond to be left fish-free for at least 7 days at >20oC usually eliminates the white spot parasites.
It has been reported that some fishes that recover from the infection will develop immunity to the disease.
This article taken from Loh & Landos (2011) Fish Vetting Essentials, Richmond Loh Publishing, Perth.
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