How to Deal with Parasitic Infections in your Aquarium


Tropical fish are unfortunately vulnerable to a number of parasites, which may seriously threaten their health. Some parasites are highly specific, tending to attack only particular groups of fish, while others may infect any species. Fish parasites may be broadly divided into two groups – external and internal: external parasites produce visible symptoms on the outside of the fish’s body, whereas internal parasites may occur in the intestinal tract, for example. This type of problem usually results from the introduction of an infected individual to the aquarium, highlighting the value of isolating any new aquisitions in a separate tank before you add them to the main aquarium.

While spot

This is probably the most common of the various protozoal diseases. It is sometimes known as ‘ich’ because it is caused by a unicellular micro-organism called Ichthyophthirius multifiliis. An infection of this type can seriously damage the fish, with certain species such as black mollies (Poecilia splwnops) apparently being more susceptible than others.

The obvious symptom of the disease is the presence ol the tiny white spots which appear all over the fish’s body, but this is only one part of the parasite’s life cycle.

The spots then rupture, giving rise to tomites, which are the parasites at their free-living stage. Each spot can produce as many as 1000 tomites. In the wild, relatively few of these would be able to locate a suitable host, but within the confines of the aquarium, where the stocking density is often relatively high, all the occupants are then at serious risk of being attacked by the tomites.

These tomites must find a host almost immediately – typically within a day, depending on the water temperature – otherwise they will die. Once they come into contact with a fish, they embed themselves in its body, forming the trophozoite stage which ultimately gives rise to the characteristic white spots. The fish’s body then becomes damaged by the parasites, and these areas are much more susceptible to attack by other microbes, especially types of opportunistic bacteria and fungi. Weakened by recurrent white spot infections, affected fish soon start to die, while treatment can only be effective against the tomite stage in the life cycle. Work is progressing on the development of a vaccine, but proprietary remedies should give good results if applied at the correct stage.

Unfortunately, it appears that some fish may carry this infection without showing clinical signs unless they are stressed, so you may not notice crucial warning signs. This explains why white spot sometimes crops up unexpectedly in an established community aquarium. Never use the same net between an aquarium where white spot is present and a healthy tank, because you will almost inevitably transfer some tomites in the droplets of water adhering to the net.

Velvet disease

This disease is caused by another protozoal parasite called Oodinium. Danios and labyrinth fish are among the most susceptible tropical species to velvet disease. Fish that have become infected often scrape themselves on rocks and other objects in the aquarium to ease the irritation caused by these parasites boring into their skin. If you look closely, you may notice that affected fish have a yellowish-grey hue on their bodies. There may also be some obvious yellow speckling, especially on the fins if these are normally clear, which is why this illness is also sometimes called ‘gold dust disease’.

It is vital to remove any affected fish as soon as you spot any warning symptoms, and treat them without delay, partly to reduce the likely spread of infection. In some fish, you may notice their breathing has become more laboured than usual – a likely indication that the gills have been attacked by the parasites. At this point, the fish may die suddenly since their ability to extract oxygen from the water will be severely reduced.

Oodinium is an unusual microscopic organism, which is part animal and part plant. Like plants, it contains the green pigment chlorophyll so it can make its own food by photosynthesis, but it also hunts microbes. After attaching to the fish for up to a week, each parasite swells up and ruptures, releasing as many as 200 spores. In an aquarium, these spores have little difficulty in finding a host to infect, and so the cycle continues. They anchor themselves on the fish’s body by developing a root-like structure.

It is a good idea to raise the water temperature slightly, because this increases the speed of the parasite’s life cycle. As a result, the spores must find a host more quickly, or they will die in as little as just one day. Without this catalyst of increased temperature, they may survive for five days or even longer.

Neon tetra disease

In spite of its name, this illness also affects fish other than neon tetras (Paracheirodon innesi), although it is most commonly associated with this species. One of the most characteristic signs of the disease is a loss of coloration, usually a pale area that spreads over part of the body below the dorsal fin; in neon tetras themselves, the distinctive red stripe running down their sides becomes noticeably less vivid.

The infection results from a microsporidium parasite called Pleistophora hyphessobryconis, which cannot be treated with any great success at present. Even if any fish do survive, the likelihood is that they will retain the organism in their body and so continue to represent a hazard to other fish. In fact, this is how the infection is usually introduced to the aquarium. Fish that are apparently healthy may carry the infection, releasing the infective spores when under stress. Like those of similar parasites, the spores spread rapidly to Other susceptible individuals in the aquarium.

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About the Author: Fred Goodson has a passion for pets and animals. He has 4 dogs and is planning to have another one. He is also a blogger who writes about pets and animals. Currently, he is living in New Jersey.

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