Editor’s Note: Remember to check out our Pest Database.

Most saltwater aquarists are acutely aware of the subjects of Cryptocaryon irritans (saltwater ich) and Amyloodinium ocellatum (velvet) infections in tropical marine fish. However, these are not the only external parasites that are problematic in the hobby. Awareness of the symptoms and treatments for other common parasites can save aquarists from disappointing setbacks, unnecessary expenses and the loss of livestock. This guide is intended as a tool for hobbyists and not as a substitute for properly identifying parasites or other pathogens with the aid of a microscope or other laboratory diagnostic tools.

The first place to start whenever you suspect that your fish are not in the best possible health is to check the water quality. Test all of your water parameters as fish health problems frequently begin and end here. With good water quality, a low stress environment and an adequate diet the animals may recover without further efforts.

Even when all the parameters are within acceptable levels, fish may respond positively to a water change. Mix and aerate fresh saltwater for at least twenty-four hours prior to use. This allows enough time for the water chemistry to stabilize and salts to dissolve completely. Match the parameters of pH and temperature closely to your aquarium. Salinity is less critical, unless invertebrates are housed in the aquarium.

There are many questions that you should ask yourself before considering what course of action to take. Consider the recent history of the animals and the aquarium for possible reasons that the fish may not be in top condition. Have you added any new animals to the aquarium in the past few weeks? When was the last addition to the tank? Do you quarantine all newly acquired fish prior to adding them to your display tank? Have you made any changes in equipment? Are you using any new foods or is it time to add more variety to your stock’s diet? How does the aquarium smell? Does the water look cloudy when you view the tank from one end? Have you noticed any aggression between inhabitants?

Have you noticed any changes in the behavior of your stock? Are all the fish eating as well as usual? Do their colors look as vibrant as ever? Are the fish active and alert? Do they scratch themselves on objects in the aquarium, or have you noticed any change in their respiration rate? Behavioral changes can be the first signs of trouble. Observe your fish daily so that you will notice any changes in behavior quickly. Don’t miss the early warning signals that the water quality, history and behavioral changes can provide.

Check the fish for visible symptoms of disease prior to moving them to a treatment tank. You can examine the fish while they are still in your aquarium by trapping them against the glass with a net or container. Then take a close look using a bright light and a magnifying glass. This will give you a much better way to examine the fish than when they are freely swimming around the aquarium.

Brooklynella hostilis

Brooklyella hostilis can infect a wide range of marine teleost fish. It is most frequently seen in clownfish and seahorses, especially wild-caught specimens. This is an opportunistic parasite that often infects animals in poor conditions or those that have been badly stressed or recently handled. Ammonia poisoning may make fish more susceptible, because of the damage it can cause to the skin and gills.

Brooklynella hostilis causes rapid mortalities while feeding on the epithelial and blood cells in the skin and gills. The most serious damage is to the gill epithelium. Infection is often accompanied, as with many types of external parasites, by secondary bacterial infection. Cause of death is the loss of epithelial leading to an impaired ability to maintain osmotic balance.

Reproduction

Reproduction is by simple cell division. Transmission is from fish to fish so the close proximity of other fish is a factor.

Symptoms

Body lesions first appear as small discolored foci that grow in size and spread. These lesions are usually seen in the areas around the head and gills. Look for lethargy, loss of appetite, hyper-secretion of mucus, hiding, respiratory distress, cloudy eyes and open gill covers. As the infection worsens the epithelium will slough off. This can have the appearance of string-like material hanging from the fish. Weight loss, as the fish lose the ability to osmoregulate, is seen in advanced cases. Secondary bacterial infections can take hold as the infection progresses.

• Discolored areas of skin that grow in size and spread
• Excess mucus production
• Loss of appetite
• Lethargy
• Respiratory distress
• Hiding
• Open gill covers
• Sloughing off of epithelium
• Cloudy eyes
• Weight loss
• Hanging at the surface or sitting on the bottom of the aquarium
• Secondary microbial (bacterial or fungal) infection

Treatment

The most effective treatment for brooklynellosis is a series of three formalin dips, one every third day for forty-five minutes. However, formalin should not be used with fish that have recently been handled, injured or exhibit open wounds. Catch the fish for treatment using clear plastic bags or containers and avoid using nets that will damage the mucus layer, or tissues of the fish.

If the fish are injured or have open wounds then place them in a low salinity quarantine tank (approximately 14ppt salinity) for at least twenty-four hours before proceeding with formalin dips. Add a polymer such as Pro Tech Coat Marine™ or StressGuard™ to the quarantine tank to serve as a temporary mucus layer substitute.

Keep the fish in a hyposaline (low salinity) environment between treatments. This should help alleviate some of the difficulty in maintaining osmotic balance that is associated with Brooklynella hostilis. Leave the fish in a cycled quarantine tank for seven days or more after all treatments are completed.

Some authors suggest combining formalin with malachite green in the treatment dips. My preferred method excludes the use of malachite green, because of the additional toxicity and subsequent stress it adds to fish that are already in a weakened condition. Antibiotic treatment may be necessary if a secondary bacterial infection becomes apparent.

Turbellarian Infection

Turbellarian infection is commonly referred to as “Black Ich” or “Tang Disease” by hobbyists. This is a parasitic flatworm that attacks the skin and gills. The parasite causes a hyper-melanization reaction leading to dark foci (black spots) on the skin. While it is most easily seen on light colored fish such as “Yellow Tangs”, it is not limited to tangs. Turbellarian infections have been reported in wrasse, angelfish, gobies butterflyfish and opisthognathids as well.

Reproduction

Reproduction is similar in many ways to Cryptocaryon irritans (saltwater ich). The parasite feeds on the host for about six days and then exits the fish to grow and reproduce. Newly hatched juveniles then find a new host or re-infect the original one. However, unlike Cryptocaryon irritans, turbellarian worms can also spread directly from fish to fish. Because this parasite has the ability to reproduce off of the host, it may be necessary to leave the display aquarium without fish for several weeks to reduce the chance of re-infection.

Symptoms

Look for small, black, pepper-like spots, mainly on the body of the fish. Infection can lead to dermatitis, inflammation and hemorrhages of the skin and secondary bacterial infection. The fish may flash (scratch) against objects in the aquarium, be lethargic, have faded colors and may stop eating.

• Black spots with a pepper-like appearance.
• Faded colors
• Flaking, inflammation or hemorrhaging of the skin
• Scratching
• Ragged fins
• Lethargy
• Loss of appetite
• Secondary microbial infection

Treatment

Several different methods of treatment can be successful. Freshwater dips may work with light infections. Formalin dips usually work well. Organophosphates can also be effective. Repeated treatments are recommended. Formalin should be used in a series of three dips, one every third day. If you chose freshwater dips, then administer a series of at least three treatments once every other day. Organophosphates should be used for three consecutive days. Be aware of the possibility of secondary bacterial infection due to wounds caused by this parasitic worm.

Monogenetic Trematodes

Monogenetic trematodes are common parasites, which feed on superficial layers of the skin and gills, consisting of about fifteen hundred species. Sometimes they are referred to as skin, gill, or eye flukes. Monogenetic trematodes can be present in low numbers without causing a problem. Heavy infection is a good indicator of poor water quality and other stressful conditions such as crowding. Serious infections can lead to secondary bacterial or fungal infection. Transmission in viviparous species can occur fish to fish.

Reproduction

Viviparous species reproduce on the fish. Oviparous species lay eggs that usually fall off of the fish to develop and hatch. After hatching the infective stage seeks out a host. The reproduction rate is generally influenced by water temperature with the population doubling in as little as twenty-four hours. The eggs of some species take 10 – 21 days to hatch (temperatures of 68 – 77F) necessitating weekly treatments for at least three weeks. Monogenetic trematodes starve within a few weeks without a host fish. Considering that the eggs of some species take up to three weeks to hatch, it may be wise to leave a system fishless for more than thirty days to clear the system of this parasite.

Symptoms

Flukes are often too small to be seen with the naked eye. Cloudy or irregular areas on the skin, focal hemorrhages, hyperplasia, eroded fins and excess mucus production are symptoms with species that attack the skin. Respiratory distress, hanging at the water surface, sitting on the bottom, weight loss, open gills covers, or opening one gill at a time can indicate parasites in the gills.

Capsaloidea are large worms that can induce scratching on objects in the aquarium. Neobenedenia melleni is a large species with a predilection for the eyes. They can cause serious damage to the eyes and skin. Microcotyle species are commonly found on the gills of angels and butterflyfish. They may not cause obvious symptoms until the infection is advanced.

• Cloudy or irregular areas on the skin
• Focal hemorrhages
• Hyperplasia (abnormal growth of cell tissues)
• Eroded or frayed fins
• Excess mucus production
• Respiratory distress
• Hanging at the water surface or sitting on the bottom
• Open gill covers, especially one side at a time
• Weight loss
• Scratching

Treatment

Formalin, organophosphates or freshwater dips are all potential treatments. Freshwater dips may work for some species. Others may require a series of formalin dips. A long-term treatment in hyposalinity may be effective against Neobenedenia melleni as egg viability is significantly reduced at salinities of less than 20ppt. The gill parasites may be more resistant to treatment than skin parasites.

You may have to experiment with treatment as resistance varies with the species of monogenetic trematode. Organophosphates, freshwater dips, formalin dips, hyposalinity and copper have been used with some success. Other drugs such as medendazole, benzocaine, and in particular praziquantel, have also been successful. Praziquantel is safe and may be the preferred treatment. If praziquantel treatment is not successful then another method will be necessary. Cleaner wrasse and neon gobies seem to eat some of these parasites, although it is uncertain if they can control a heavy infection.

Trichodina

There are about 70 marine species of Trichodina. Common species feed on skin, mucus and blood on the skin and gills and can damage tissues with their constantly beating cilia. They are sometimes called “Flying saucers”, because of their resemblance under a microscope. Smaller species tend to infect the gills and are limited in the number of species of fish on which they are found. Larger species appear to prefer the skin and are less host specific.

Reproduction

Reproduction is by binary fusion and conjugation. Transmission is direct. However, under normal conditions, trichodina are harmless. They usually do not become problematic unless the potential hosts are in a weakened condition due to stress or disease.

Symptoms

Look for respiratory distress, skin damage, scale loss, open gill covers, clamped fins, red bloody patches and scratching. Infections are usually chronic rather than acute. Severely infected fish can become anorexic and lethargic.

• Skin damage and scale loss
• Respiratory distress
• Red bloody patches on the skin
• Open gill covers
• Clamped fins
• Scratching
• Loss of appetite
• Lethargy

Treatment

Fish are usually resistant to trichodina when provided a low stress environment, good water quality and an adequate diet. A large water change using well aged and aerated saltwater is a good first step. Fish may recover without treatment when provided with improved water conditions. One freshwater or formalin dip is usually all that is required to rid fish of trichodina on the skin and gills.

Uronema marinum

Uronema marinum is a free-living rather than obligate parasite as it feeds on live food, dead tissue and bacteria. However, this parasite is opportunistic and, it is often found on recently captured, transported, or otherwise weakened hosts. Poor conditions and stress are believed to be factors as they negatively impact the host’s immune system. Uronema marinum infects fish within a wide temperature and salinity range and invades the internal organs in advanced stages.

Reproduction

Reproduction is by fission.

Symptoms

Early on, increased mucus production and hyperactivity may be seen as symptoms of Uronema marinum infection. Focal de-pigmentation, ulceration and pitting of the skin, respiratory distress, lethargy, flashing, clamped fins, erratic swimming, gasping at the surface or laying at the bottom of the aquarium are symptoms. Raised scales with bloody patches (hemorrhages) can also be exhibited. These lesions can be difficult to distinguish from those exhibited with vibrio bacterial infections.

• Excess mucus production
• Hyperactivity early in infection
• Focal de-pigmentation
• Ulceration and pitting of the skin
• Respiratory distress
• Lethargy
• Clamped fins
• Gasping at the surface or sitting on the bottom
• Raised scales with bloody patches
• Flashing
• Erratic swimming

Treatment

It is crucial to begin treatment early before this parasite invades internal organs. Early stages of infection may be controlled with freshwater or formalin dips (Basiola and Gratzek,1992.). Some success has been reported with nitrofurazone and methylene blue (Chueng et al., 1980. Bassleer, 1983). Experimental treatments with anti-malaria drugs such as chloroquine and quinacrine hold some promise. Hydrogen peroxide can be effective against parasites on external surfaces, but it is not well tolerated by some fish. Systemic infections have a poor prognosis. Secondary bacterial infection is common. It may be wise to follow formalin or freshwater dips with a course of nitrofurazone treatment.

Definition of Terms

Osmoregulation (process that controls the salt/water balance within fish) Pronounced: os·mo·reg·u·la·tion. The regulation of osmotic pressure. The control of the concentration of dissolved substances in the cells and body fluids of an animal.

References

1. Blasiola GC: Diseases of Ornamental Marine Fishes. In Gratzek JB, Matthews JR editors: Aquariology: the science of fish health management, Morris Plains , NJ., 1992, Tetra Press, pp. 275-300.
2. Bassleer G: Uronema marinum a new and common parasite on tropical saltwater fishes, Freshwater Mar Aquar 6:14:78-79, 1983.
3. Cheung PJ, Nigrelli RF, Ruggieri GD: Studies of the morphology of Uronema marinum Dujardin (Ciliata: Uronematidae) with a description of the histopathology of the infection in marine fishes, J Fish Dis 3:295-303, 1980.