Parasitic diseases are a major problem for aquarium fishes. Almost all marine fish have parasites to some degree. Protozoan, small microscopic animals generally invisible to the naked eye, are the most serious types of parasites. There are numerous parasites responsible for diseases of marine fish; this discussion will be limited to the most common parasitic problems known to occur under aquarium conditions: Coral Reef Disease, White Spot Disease, Clownfish Disease, Black Ich, Flukes.
Coral Reef Disease
Coral Reef Disease is one of the most common diseases of freshwater and marine fish, which can rapidly cause death if not treated promptly. The parasite primarily attacks the gills, body, and fins of the fish. The parasite, which is a small protozoan, is introduced into the aquarium through nonquarantined fish. The disease is rapidly transmitted from infested fish to other fish in the aquarium. During the life cycle of the parasite, it first develops on the fish's body and when mature drops to the aquarium bottom. The parasite encysts, then undergoes cell multiplication to form small free swimming parasites called dinospores. These young parasites are released from the cyst and infect other marine fish. Coral reef disease must be treated as soon as the disease is identified. A delay in treatment can result in the death of all your aquarium fish.
White Spot Disease
"White spot disease" or "Ich", is a primarily cutaneous infection of freshwater and marine fish caused by the protozoan parasite Ichthyophthirius multifilis. Ich most often causes the appearance of small white spots over the body and fins of fish. However, it is important to note that Ich can present with many different appearances, and that other things besides Ich can cause small white spots on the body. Thus, the only sure-fire way to know that what you're treating is Ich is to scrape the skin of your affected fish and look at the scraping under the microscope. For those of you interested in looking at things under the microscope, Ichthyophthirius is a large ciliated protozoan with a U-shaped micronucleus. Its shape changes as it moves through the water, and it appears to "tumble" as it moves. For those of you not interested in skin scrapings, you can have a high rate of success just assuming that what you're treating is Ich. To effectively treat Ich, it's important to understand a little bit about the life cycle of the organism:
1. The adult stage lives on the skin and body of the fish. It will burrow under the epidermis, causing skin damage. Disruption of the skin leads to osmoregulatory disturbances, osmotic stress, and allows for the easy entrance of secondary invaders like bacteria.
2. The cyst stage lives on the bottom of the aquarium, and gives rise to about 300 tomites per cyst.
3. The tomite stage is the only stage which is sensitive to the medication! The life cycle takes 12-16 days to complete, depending on the temperature, and the tomite stage lasts for only three days.
All of these facts may seem trivial, but they are important because they dictate what treatments will be effective.
Black Ich disease appears as small black spots distributed over the fish's body. The spots are about half the size of a pinhead or smaller. They are primarily found on the body and are are especially easy to see on light-colored body areas or on the transparent areas of the fins. Affected fish will scratch on the bottom or other aquarium objects. Other signs of the disease include lethargy, development of a pale body color, and lack of appetite. The disease is caused by a small worm known as a tubellarian. After parasitizing a fish, the worms develop on the fish's skin and gills and acquire dark pigmentation. They are freely mobile and will tend to move over the surface of the fish. After five or six days depending on the environmental conditions, they drop to the bottom of the aquarium. There they mature, with the development of the young worms within their body. Once the development of the young is complete, the adult worms burst, releasing the free swimming young that infest new host fish. The worms can be controlled with various commercially available medications. Formalin based products or those containing organophosphate compounds such as trichlorfon appear to be the best medications. In addition to the use of medications, any excessive buildup or organic material and debris should be siphoned from the aquarium several times during treatment. Since the young worms develop on the aquarium bottom, the removal of debris will aid in controlling the disease by reducing their numbers.
Flukes attach to fish by means of a special organ called a haptor, which is equipped with hooks, clamps, and anchors used to firmly attach the worm to the fish. Flukes are freely motile, moving over the fish's body or gills causing extensive damage to the fish through their movements. Flukes reproduce on the fish, with some species producing hundreds of eggs on the gills and body, which then hatch into free-swimming larvae. The larvae reinfect the host fish or attach to other fish. Other fluke species are viviparous, meaning they give birth to living young rather than eggs. Affected fish show various abnormal behavior changes, including scratching, which is the most obvious sign of infestation. Other signs include increased respiration and change in body color. In sever infestatios ulcerations may also be noticeable. These troublesome parasites can be controlled by various treatments, including freshwater dips,formalin-based medications or the use of ganophosphates.Freshwater dips are easily performed and often very effective in reducing the number of flukes on the body of the fish. Formali-based medications and organophosphates have been used for many years with excellent success in treating flukes.
Clownfish Disease is a serious malady affecting Clownfish or sea horses, and other kinds of marine fish.Various species of Clownfish are particularly susceptible to infection from this parasite. The disease is caused by a small ciliated protozoan invisible to the naked eye. It is a parasite of the gills and skin, and unlike the other protozoan discussed, the life cycle is simple, with the parasite reproducing by cell division. As a result the parasite multiplies rapidly on affected fish, causing mortalities in a short period of time. Affected fish develop body lesions, excessive slime secretion, and increased respiration. In the early stages of the disease all that is noticed is an abnormal paleness of color and a rapid breathing rate. As the disease worsens, lesions will be observed on the body, with sloughing of the skin and mucus. The development of a secondary infection with bacteria often accompanies infestation with the parasite. Clownfish Disease is capable of killing fish within 24 to 36 hours after appearance of the signs of scratching and heavy respiration. Prompt treatment must be instituted if the disease is suspected. The parasite is sensitive to various medications, which can be purchased under various trade names. It is recommended that the fish with Clownfish Disease be treated with medications that contain formalin or malachite green. Medications containing copper should be avoided, as the disease is not readily controlled by copper based chemicals.