Diseases of the Skin, Muscle, Gill and Fin
The disease is common in the southern parts of the province, but can be found almost everywhere. The bacteria that causes the disease (Aeromonas hydrophilia), are normal inhabitants of surface water. They will cause disease in fish which are stressed, traumatized, overcrowded or in abnormally warm water or low oxygen conditions. The bacteria enter the fish via the mouth or a wound and enter the blood stream where they multiply and spread to affect many organs. Large numbers of fish can be affected and the majority die.
Human safety: Fish affected are in poor condition. Flesh of the infected fish may have an off taste and should not be eaten. This bacteria is found in untreated water and is not considered harmful to humans (under normal circumstances). Aeromonas species has been known to cause diarrhea in children and various infections of the skin, eye and other organs. Persons in contact with the fish should wash their hands thoroughly. This bacteria produces some toxins which may cause food poisoning.
This bacterial caused disease is found in warm water above 18 degrees Celsius. The Flexibacter columnaris bacteria can be found on the skin of normal and diseased fish. Infection and disease are the result of a loss of balance between the host fish's immune system and the multiplication of bacteria. Poor water quality and oxygen levels can predispose a fish to this disease. Once infected, fish do not eat; they deteriorate and die.
Human Safety: Flexibacter bacteria are not known to infect humans. Diseased fish should not be eaten because of poor quality of the flesh.
The bacteria (Aeromonas salmonicida) can infect fish which ingest contaminated feces from infected fish or through direct contact with infected fish. Normal mucous and intact skin along with normal bacterial microflora offer protection against this disease. Fish can recover but many die. Stressers include low oxygen levels and warm water. Loss of mucous or skin abrasions make individuals more susceptible to infection.
Human Safety: Affected fish are in poor condition and flesh may not be appealing in taste and should not be eaten. Aeromonas species has been known to cause diarrhea in children and various infections of the skin, eye and other organs. Persons in contact with the fish should wash their hands thoroughly.
While this disease is not that common in Saskatchewan, it has been reported in cold water of northern regions. The bacterium Flexibacter psychrophila is suspected to live on the skin of healthy fish and in water containing high levels of organic material. Mortality is high among fish affected by this disease, however some fish do appear to recover. The optimum temperature range in which the bacteria flourish is 4 to 12 degrees Celsius.
Human Safety: Diseased fish should not be eaten because of poor quality of the flesh.
This fungal disease is common throughout Saskatchewan. The term Saprolegniasis is used to describe fungal infections of the skin and gills caused by a variety of fungi. A combination of trauma (such as rough handling by anglers), overcrowding, pollution, cold temperature and/or bacterial infection can predispose a fish to a fungal infection. Severely infected fish usually die.
Human Safety: Fungi are common in natural water. Affected fish should not be eaten because of the poor quality of flesh. Hands should be thoroughly washed after handling affected fish.
This type of infection can occur in almost all waterbodies in Saskatchewan. Adult tapeworms in the intestine range in size from microscopic to 20 centimetres in length.
In general, the life cycle of a tapeworm requires three hosts. Adult worms can be found most commonly in the intestines of the final host. Final hosts include mammals (including humans) and birds which eat fish. Infective stages of the tapeworm are released into the water in the feces of the final host. These infective stages are ingested by intermediate invertebrate hosts and develop to more mature larvae.
The infected invertebrates are eaten by fish fry or other invertebrate eating fish which become the second intermediate hosts. In this host, the tapeworm larvae escape the intestines and migrate to internal organs and muscles where they encyst. It is these cysts and the reaction to these cysts that cause the lesions seen. As second intermediate host age, they tend to accumulate a large number of these cysts. If the sex organs are affected, sterility can result. Death can be caused by the damage to organs (eg. heart) caused by the migration of the parasites.
The fish-eating mammal, bird or predator fish become the final host for the tapeworm by eating the cystic second intermediate host fish. The encysted tapeworm larvae mature in the intestines of the final host. The adult worms usually cause no obvious disease in the final host unless the load is heavy or the adult worm is extremely large in comparison to the final host.
Examples:
1. The first intermediate host of one type of tapeworm is a copepod (small crustacean). A second intermediate host is a fry (including northern pike fry). The final host is a northern pike and the adult tapeworm can cause erosions and ulcers in the intestines of the pike.
2. The first intermediate host of a second type of tapeworm is a copepod. The second intermediate host is a fish (trout or walleye) and the final host is any mammal, including humans.
Human Safety: Humans, dogs and many other species such as bears and fish-eating birds that eat raw or poorly cooked fish are vulnerable to infection by this parasite. The effect in humans is the development of tapeworms in the intestine.
Black spot is caused by the larval form of a fluke and the infection is common to North America and can cause great losses in pond-reared fish. The term "Black Spot" refers to the formation of small cysts in the muscle and skin around which the parasite lives. The cyst accumulates black pigment cells. These cause little harm to the fish. Young fish have growth problems if heavily infected. The first intermediate host is a mollusc. The fish is the second intermediate host and the final host is a kingfisher or heron.
Human Safety: The unsightly nature of this parasite when fish are heavily infected makes this fish unsuitable for human consumption.
This infection is common throughout Saskatchewan in freshwater fish. It is caused by a small parasite which encysts as it develops. At maturity, the cyst ruptures, releasing spores into the water. The spores become infective and enter other fish by attaching to gills and breaks in the skin. Hemorrhage and cell damage results in an open ulcer on the skin or gill. By occupying space on the gills of the fish, the parasite can interfere with normal respiration. Many fish survive with low levels of infection.
Human Safety: These infections spoil the appearance and taste of the fish, making the fish unsuitable for human consumption.
Also known as Ichthyopthirius, this infection is found in most waterways of Saskatchewan. The small. self-propelling protozoa likes warm temperatures and can complete its life cycle in 12 hours. Each individual organism that erupts from the skin of the fish can produce 2,000 infective feeding stage protozoa able to infect other fish. A white spot is caused by the organism rotating in the skin as it feeds.
When the organism is mature, it ruptures through the skin causing severe trauma. Secondary infections by bacteria and fungi can then occur. The fish can die from these secondary infections, as result of the loss of the protective skin barrier or from loss of function of severely affected gills. Fish which survive an infection appear to be resistant to reinfection for several months.
Human Safety: Heavily infected fish are unsightly and loss of skin causes the flesh to be spoiled. The severely affected fish is not suitable for human consumption.
Attachment of the leech Piscicola sp. is common in all areas of Saskatchewan, but is more common in the southern regions. The leeches live in the water and occasionally attach to the skin of the fish to obtain a blood meal by boring a hole through the skin. Heavy infestations usually occur on cultured fish in highly infective environments and can cause death.
Human Safety: If leeches are removed from the fish and no secondary infections are apparent, the fish is safe for human consumption.
This "disease" is more common in the southern areas of the province, but can occur anywhere. The free swimming larvae of many bivalve molluscs must go through a parasitic state on the skin or gills of fish. The larvae becomes surrounded by fish tissue on the gills and may stay there for seven or eight months while maturing. High mortality of fish is rare, but has been reported in hatchery environments. Death can result due to loss of useful gill function. Some other crustaceans have a direct life cycle in which an adult lays eggs in the water and the hatched larvae must find a fish to attach to within a couple of days. The damage to the skin can cause secondary infections (bacterial and fungal).
Human Safety: Unsightly fish due to massive sores caused by infestation of large numbers of crustaceans should not be eaten. Most mollusc infections of the gills go unnoticed.
Lymphocystis is caused by a virus that invades the fish through breaks in the skin. Such skin wounds are a common occurrence in late spawning season as large numbers of fish in small areas constantly damage their skin. Each skin wound mass swells up to 100 fold larger than normal. These infected cells can each be seen with the naked eye as cyst-like structures. The disease does not cause great harm to the fish unless the masses are extensive. Masses on gills can cause problems with respiration. Fish with lymphocystis can recover and be reinfected.
Human Safety: The virus is not known to infect humans.
These types of tumors are found in affected fish sporadically throughout North America. Fibromas are solitary distinct masses while fibrosarcomas are cancerous (invading). Little is known about the cause of the tumors, but both infectious agents (virus) and environmental factors (genetics) are suggested as possible causes. The disease leads to death of the tumor becomes extremely large and impairs the fish's ability to forage and flee from predators.
Human Safety: There is no evidence to link fish and human cancers, however, the cause of some cancer tumors is viral. Fish infected should not be consumed by humans or domestic animals.
Reported throughout North America and the world, this type of malignant tumor is caused by a virus. In northern pike, the virus invades the white blood cell (lymphocyte). The cancerous white blood cells progress from the skin and muscle to infect internal organs. Over 99 per cent of fish infected die.
Human Safety: Any fish with a tumor is considered unsuitable for consumption by humans and their pets.
This disease, common is Saskatchewan, has been reported in spawning walleye. A retro virus causes this locally invasive tumor by invading damaged skin. The virus infects cells and causes them to multiply uncontrolled.
Human Safety: Any fish with a tumor is considered unsuitable for consumption by humans and their pets.
This disease has been reported in recently translocated fish and fish near warm water outflows. It can be a result of man-made or natural changes in the gas content of water. During times of rapid plant growth and oxygen release, water can greatly increase its dissolved oxygen levels. Man-made outflows may have high gas levels due to the temperature of the outflow or the mechanical pumping of the water. The dissolved gases are absorbed by the fish, but when the gases enter the bloodstream, they come out of solution to form gas bubbles. This disease is more common in cultured fish. Young fry are killed by this disease while adults have a better chance of recovery. Permanent damage to the eye can result and the survivability of a fish which recovers is poor.
Human Safety: Fish are usually found dead or in a state of decomposition. Fish caught with this condition should be safe to eat.
Muscle atrophy (or muscle wasting) is reported in waterbodies of Saskatchewan and other provinces. Muscle loss is seen in fish with disease of the pancreas or in starved animals and appears to be compounded by cold water temperature. The condition can be reproduced in the lab by feeding the fish a diet low in Vitamin E and selenium.
Human Safety: Fish in this state are unsuitable for human consumption as the disease affects the texture and taste of the muscle.
The loss of muscle seen often in the walleye appears different from starving fish. Some researchers suggested this disease is a result of injury associated with gill netting while others strongly dispute this theory.
Human Safety: Fish in this state are unsuitable for human consumption as the disease affects the texture and taste if the muscle.
The discoloration of the flesh of fish can occur anywhere and is common in waterways with an abundance of algae and plant life. Not a true disease, this condition is due to food consumed by the fish. The pigments which are present in plants and invertebrates are absorbed from the gut and deposited in the muscle. The resulting discoloration depends on the plant product eaten.
Human Safety: There is no harm in eating this type of affected fish. Farmed rainbow trout are fed extra pigments in order to produce a brighter color of flesh.
Trauma to fish is found in spawning grounds, waterways with man-made dams, fish farms, commercial and sport fishing. The disease state can result from natural or man-made causes. During spawning season, many fish crowd together and can cause damage to each other. Some fish are traumatized when released from deeply imbedded or barbed hooks which leaves wounds that may become secondarily infected with bacteria, viruses or fungi. Turbines, water inlets and other man-made structures can provide a dangerous damaging obstacle for migrating fish. Netted pens can wear fins and tails as fish school constantly in large groups (over 10,000).
Human Safety: Affected fish should be eaten at the discretion of the angler. Flesh quality may be affected by secondary infections resulting from wounds.
