Aquarium Fish-Diagnosis, Diseases and Treatments

Observe the activity and body language of the fish in the water. It is important to know the normal behavior of the species of fish being evaluated. For example, male bettas (Betta splendens) are often kept in small bowls without filtration or temperature control. They normally use the mid level or upper level of the bowl; however, when the temperature drops too low, they sit on the bottom and are reluctant to move. Also, the foraging behavior of certain fish may be confused with abnormal behavior.

Abnormal Behaviors Common to Sick Fish

Fish Diseases Description
Coughing flaring of the operculum followed by rapid closure in an attempt to dislodge an irritant from the gills, which is suggestive of gill disease.
Flashing rubbing against objects, which is suggestive of an ectoparasitic infestation.
Piping gulping air at the surface, indicating hypoxia due to oxygen-poor water, gill disease, or anemia.
Circling (controlled) or whirling (uncontrolled) suggestive of blindness and neurologic disease, respectively.
Drifting aimless, propelled motion indicative of weakness and imminent death.
Abnormal posture floating at the surface, which may suggest disorders such as swim bladder or neurologic disease. Or in the case of goldfish, a lack of fiber in flake food diets often results in poor intestinal motility, resulting in air accumulating in the intestines. This air causes the fish to float abnormally at the surface.

Quarantine and Initial Treatment

Isolate sick fish, especially those suspected of having an infectious disease, from other fish in a separate aquatic system until they have recovered. Consider a broad -spectrum therapy, such as a prolonged immersion with a low concentration of copper during the quarantine period. Provide Specific treatment of fish in quarantine exhibiting parasitic, fungal, or bacterial infections once a diagnosis is made.

Common Noninfectious Disorders in Aquarium Fish

Common husbandry-related disorders in fish include toxicities caused by ammonia, nitrites, heavy metals, and poisons introduced into the aquatic system.
Traumatic injury related EO capture or aggressive tank mates is another husbandry-related problem.
Lateral line erosion, or hole-in-the-head syndrome, is a condition resulting in ulceration of the skin associated with the sensory tissue on the head and lateral line of a fish. The cause of this condition is unknown, but it improves by addressing husbandry problems such as improving the diet, (feeding natural foods) and correcting water quality problems.
Air embolism, or gas bubble disease, is diagnosed by observing gas bubbles in the fins, gills, and eyes of fish. It is caused by cavitating pumps (usually requires pumps of 1/2 horsepower or larger) that force oxygen and nitrogen into solution. Cavitalion occurs when the pump sucks in air either at the intake (when an air stone is placed near the intake) or through a broken valve.
Malnutrition is another possible contributor to disease. The exact nutritional requirements of most fish are unknown, so an underlying deficiency of certain nutrients may be difficult to detect and may predispose fish to secondary diseases. Conditions such as hepatic lipidosis. emaciation, loss of dorsal musculature, disproportionate bodies (big heads and small bodies), and gastrointestinal disorders (e.g. constipation) are most likely directly related to the diet. Obesity and hepatic lipidosis are associated with a high dietary fat intake. Ideally, fish should be fed a diet identical to their natural diet.

Common Infectious Disorders in Aquarium Fish

Pet fish are susceptible to bacterial, fungal, and viral infections as well as parasitic infestations. A common husbandry-related cause of infectious disease is failure to quarantine new fish before introducing them to the established system. As a result, outbreaks involving pathogenic organisms occur.

New fish should be quarantined in a separate system for four to six weeks before, their introduction into an established system with other fish. Monitor fish in quarantine for clinical signs of disease. Consider a broad-spectrum therapy, such as a prolonged immersion with a low concentration of copper (see boxed text titled “Copper treatment” on page 851) or formalin, as a prophylactic treatment.

Bacterial Infections in Aquarium Fish

Bacterial disease is one of the most common causes of aquarium fish mortality. Most pathogenic bacteria are gram-negative aerobes and facultative anaerobes. Immunosuppression due to stress, poor nutrition, a poor environment, or parasitic infestations often leads to bacterial infections with opportunistic pathogens.
Clinical signs may vary but. often include lethargy, anorexia, hemorrhages (erythema of the fins, mouth, or vent), cutaneous ulcers, fin rot, ascites, exophthalmia, abnormal posturing, and color change. During postmortem examinations, the kidneys provide the best location for bacterial culture in suspected cases of bacteremia or septicemia. Bacterial cultures are best performed by microbiology laboratories that routinely culture pathogenic bacteria from fish.
Fish with bacterial infections can be treated by placing antibiotics in gelatin diets, giving commercially medicated foods, loading food with the antibiotic, or medicating by stomach tube. Antibiotics can also be delivered by intramuscular or intra colon injection or through the water either as a bath (10 to 60 minutes) or prolonged immersion ([greater or equal] 24 hr). Most treatments are empirically derived, but formularies are available to guide antibiotic therapy

Fungal Infections in Aquarium Fish

Fungal infections, another important cause of disease in fish, are usually the result of immunosuppression associated with poor water quality, stress, and other diseases. Prolonged treatment with antibiotics may also predispose fish to fungal infections. Saprolegniasis is a catch-all term for while, fuzzy mold growth on this skin of fish.

Saprdegnia is a genus of water mold that commonly infects fish and their eggs. Immunosuppression, resulting from, for example, a drop in temperature or stress from overcrowding, can predispose fish to such fungal infections. Fish with fungal infections are treated with antifungal agents given orally in food, by injections, or by the water-tome route.

Viral Infections in Aquarium Fish

Fifty-six viruses have been reported in fish. Viral diseases are frequently associated with secondary bacterial, fungal, or parasitic infections that may lead to a mis-diagnosis.
Lymphocystis disease, one of the first viral diseases described in fish, is common to freshwater and marine fish. It is caused by a DMA iridovirus, and infected cells (fibroblasts) increase up to 50,000 times normal size. Advanced lesions exhibit large wartlike tumorous growths on the skin and fins.
The disease is transmitted by direct contact and is typically self-limiting, unless growths around the mouth cause starvation. Regression of the lesions may take several months, and affected fish should be isolated from other fish. Keep recovered fish isolated for at least one month to prevent spread of the vims in other fish.
Carp pox, or cyprinid herpesvirus I or Herpesvirus cyprini, is typically a benign self-limiting disease that causes epidermal hyper-plasia that appears as superficial, soft, white to gray, waxy or mucoid lesions on the skin and fins of carp and koi. The lesions can persist for several months in affected fish, especially in cooler water temperatures, but resolve when the water temperature warms in the spring. Carp pox can result in systemic disease and high mortality in juvenile cyprinids (less than 2 months of age), such as carp and koi.
Spring viremia of carp is a reportable viral disease caused by Rhabdovirus catpio that causes high morbidity and mortality in cultivated carp, especially young carp, and related fish such as koi and goldfish. Clinical signs of this viral infection are nonspecific because multiple organs are involved; however, dropsy, darkened skin, and exophthalmia are common.
Necropsy reveals small hemorrhages throughout the body, ascites, peritonitis, enteritis, and edema of internal organs. Outbreaks of the infection are commonly seen in the spring but can occur whenever the water temperature drops below 64 F (17.8 C). A definitive diagnosis is made by virus isolation, or indirect tests such as ELISA and virus neutralization are available to detect the virus in a fish population.
There is no treatment foe this disease, but keeping the water temperature above 68 r (20 C) helps decrease the mortality. Depopulation of infected fish followed by disinfection (1 part bleach to 10 parts water) of the habitat is recommended to control the disease.
Koi herpesvirus infection is an acute viral disease that can cause high morbidity and mortality in carp and koi. Clinical signs of the viral infection are nonspecific, but severe gill lesions with red and white patches (edema and necrosis), pale raised patches of skin, and sunken eyes are common.
Affected fish may also exhibit neurologic signs such as erratic swimming and disorientation. Clinical disease commonly appears in a collection of koi and carp during the spring or summer within two to four weeks after introducing new fish to the system or returning from a koi show. The mortality related to koi herpesvinis infection typically occurs in water temperatures between 64 and 81 F (17.8 and 27,2 C).
A definitive diagnosis is based on positive results on culture or polymerase chain reaction testing (diagnostic laboratory at me University of Georgia). there is no treatment for koi herpesvinis infection, and surviving fish should be considered earners. Therefore, depopulation followed by disinfection of the habitat is recommended, to control disease

Parasitic Infestations in Aquarium Fish

Parasitic infestations are common in fish. They are diagnosed by wet mount examination of the mucus (from skin), fins, or gills as mentioned above.

Parasitic Protozoa

Ciliate protozoa have a direct life cycle, and most are commensal. However, a few are notoriously pathogenic. Ichthyophtbirius multifiliis (known as Ich) in freshwater fish and Cryptocaryon irritant in marine fish are highly pathogenic ectoparasites that feed on host cells. Trichodina species in freshwater and marine fish is another pathogenic dilate protozoan that can damage the gills and skin when large numbers of the protozoan are present.
Chilodonella piscicola and Chilodonella hexasticha in freshwater fish and Brooklynella hostilis in marine fish are ciliate protozoa that cause excessive mucus production and hemorrhage in the gills. Tetrabymena species in Freshwater fish and Uronema species in marine fish are normally free-living commensals that become secondary pathogens that are highly invasive and can be found in internal organs. Epistylis species in freshwater fish are ectocommensal ciliate protozoa that create white tufts on hard surfaces of the fish, such as the fin rays and scales
Flagellate protozoa may have direct life cycles; some have resistant cyst stages, The hemoflagellates have indirect life cycles. Ichthyohodo necator (also called Costia necatrix) in freshwater and marine fish attaches to skin and gills, feeding on host cells and causing epithelial hyperplasia and goblet cell destruction.
Amylioodinium species is a common dinollagellate parasite in topical marine fish that affects both teleost and elasmobranchs, such as sharks and rays. It is detected by identifying the trophonts in wet mount preparations of the skin or gills. Piscinoodinium species, the freshwater counterpart to Amyloodinium species, contains chlorophyll and causes velvet disease, or rust disease, in topical pet fish.
Fish with heavy infestations exhibit a rusty or yellow sheen to the affected skin. Hexamita and Spironucleus species in freshwater and marine fish are flagellate protozoa in the gastrointestinal tract of fish that can cause anorexia, lethargy, and death.
Fish exhibiting scant, mucoid feces should be examined for a possible intestinal flagellate infestation. Massive systemic infections, especially with Spironucleus species, are lethal. Other flagellates, such as Cryptobia species, can also be important pathogens. Trypanosome infections are usually asymptomatic, and their pathogenesis is unknown. Trypanosomes are incidental findings in blood films or in imprints of tissues such as the kidneys.
Other protozoal parasites include the microsporidia, such as Pleistophora hyphessobryconis in freshwater fish that causes neon tetra disease. Myxosporidia species are highly pathogenic, usually intracellular, and involve all organs.
Digenetic trematodes are endoparasites with an indirect life cycle. The indirect life cycle of digenetic trematodes involves a definitive host that is a fish-eating bird, a first intermediate host that is a snail, and a second intermediate host that is a fish. Adults live in the gastrointestinal tract and have two suckers and a Y-shaped gut.
The metacercariae encyst throughout the body of the fish intermediate host. Most fish with encysted metacercariae exhibit no signs of illness; however, those with heavily infested organs may have organ dysfunction. Encysted digeneans are difficult to treat, but praziquantel may reduce their number.

Treatment of Protozoa

Protozoal infestations are usually treated topically with medicated dips or baths. The distinction between a dip and a bath may vary among authors as does the preference for dosages, but in general a dip is exposure to a medicated solution for less than 15 minutes, whereas a bath is for a longer period.

Prolonged immersion treatments are those that provide a constant exposure of the medication over several days. Parasitic protozoa can be treated with formalin (0.125 to 0.250 ml 37% formaldehyde/L) as a one- to 60-minute bath; malachite green (0.1 to 0,15 mg/L) as a prolonged immersion; salt (10 to 30 g/L as a bath up to 30 min (a four- to five-minute salt solution dip for freshwater fish or freshwater dip for marine fish); or formalin (0.02 ml 37% formaldehyde/L) phis malachite green (0.1 mg/L) as a prolonged immersion.

Formalin solutions should not be used if they contain white paraformaldehyde precipitates.


Monogenean (skin or gill fluke) infestation occurs in both freshwater and marine Fish. Monogeneans are ectoparasites mat live on skin, gills, and fins. They contain a haptor (attachment organ) and have a direct life cycle. Dactylogyrus species has four points at the anterior end. an anterior sucker, four eye-spots, and a haptor with two large hooks surrounded by several small hooklets.

Gyrodactylus species has two points at the anterior end, an anterior sucker, no eyespots, and a haptor with two large hooks surrounded by several small hooklets. This monogenean is viviparous with internal embryos containing hooks. Clinical signs associated with monogenean infestation include flashing and skin disorders because of the injury to skin caused by the parasite’s attachment and feeding behavior. The hooklets on the haptor penetrate epithelial cells.

Treatment of Monogenean

Monogeneans can be treated by using formalin (0.125 to 0.250 ml 37% formaldehyde/1) as a one- lo 60-minute bath; praziquantel (2 mg/L. for freshwater fish or 20 mg/L. for marine fish) as a one- to three-hour bath; trichlorfon (dimethyl phosphonate; 0.25 to 1 mg/L) as a one-hour bath; or a salt bath (30 to 35 g/L) in freshwater fish.
Digenetic trematodes are endoparasites with an indirect life cycle. The indirect life cycle of digenetic trematodes involves a definitive host that is a fish-eating bird, a first intermediate host that is a snail, and a second intermediate host that is a fish. Adults live in the gastrointestinal tract and have two suckers and a Y-shaped gut.
The metacercariae encyst throughout the body of the fish intermediate host. Most fish with encysted metacercariae exhibit no signs of illness; however, those with heavily infested organs may have organ dysfunction. Encysted digeneans are difficult to treat, but praziquantel may reduce their number.

Parasitic Crustaceans

Parasitic crustaceans include the Bianchima, which arc ectoparasites with a dorsoventrally flattened body and prehensile suckers that attach to the bodies of fish. An example is Argulus species (fish louse), which has a direct life cycle and causes cutaneous lesions and respiratory distress. It is large enough to be seen grossly, and clients may observe the parasite’s movements
Copepods are another group of parasitic crustaceans with a diversity of body forms with variable appendages An example is Lernaea species (anchor worm), which is an elongated copepod that embeds its head into the skin of the fish, leaving its Y-shaped egg sacs to hang from the fish. These sacs can easily be seen grossly. The anchor worm has a direct life cycle and lives in freshwater.

Treatment of Crustacean Infestation Organophosphates

Organophosphates are the typical treatment for parasitic crustacean infestations. Dichlorvos and trichlorfon are the mast commonly used organophosphates for treating fish with parasitic crustacean, monogenean, or leech infestation. Trichlorfon (0,5 to 1 mg’L) as a prolonged immersion or dichlorvos (0.5 to 2 mg/L) as a 30- to 60-minute bath is effective.

Diflubenzuron (Dimilin–Pond Care) is a chitin synthesis inhibitor that when used at a dose of 0.01 mg/L as a prolonged immersion treatment can also rid fish of crustacean cope-pod infestation.

Copper Treatment

Copper (copper citrate or copper sulfate) is used to treat external parasites or bacterial or fungal disease. The usual therapeutic concentration is 0.15 to 0.2 ppm, except for sensitive fish. The concentration can be gradually increased (i.e. 0.01 ppm per day) to 0.2 ppm in sensitive fish. The free copper ion is the active form, whose concentration depends on the total alkalinity of the water.

A higher concentration of copper sulfate is needed to provide therapeutic concentrations of free copper ion as the alkalinity increases. Also, copper may be unstable in water with low alkalinity ( 250 nig/L). Cheated copper (e.g. copper citrate or copper EDIA) may be more stable in marine water and fresh water with high alkalinity than copper sulfate is, but its safety and efficacy are still being evaluated.

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