The disease is caused by several species of Mycobacterium, some of which can infect humans, other mammals and birds. This is not the same organism that causes tuberculosis in humans but is a related bacteria. The bacterium is hardy and can resist freezing. Fish can be infected through open wounds or by eating other animals infected with the bacteria. The disease is slow and progressive but may not cause illness in the fish until well advanced. This disease may be mistaken for diseases caused by the Flavobacterium species or protozoa. It requires microscopic examination using special stains for confirmation.

Human Safety: Fish found containing these types of nodules should not be eaten. After handling affected fish, hands should be washed with soap and water to prevent infection via cuts and scrapes.

This disease is reported occasionally in Saskatchewan. It can result from poor nutrition because the fish is mobilizing its own fat stores to the liver to be used as energy. Lipidosis can be the result of feeding on a very high fat diet. Increased fat in the liver in this disease results in an easily broken liver. Periods of loss of blood cells, due to disease or toxins, can also lead to this condition. Pen fed fish have patchy pale livers when fed rancid feed. This condition is easily confused with invading tumors or inflammation of the liver and should be examined microscopically to confirm disease state.

Humans Safety: Fish in poor condition may be poor tasting. Consumption of the fish is at the discretion of the angler. Those fish eating high levels of fat should be fit for human consumption.

These tumors originate from smooth muscle cells in the testicle or ovary in mature fish. The difference between Leiomyosarcoma (cancerous) and Leiomyoma (solitary tumor) can only be determined microscopically.

Human Safety: Food safety regulations specify all animals with tumors as unfit for human and animal consumption.

Various species of roundworms are found throughout Saskatchewan. They have larvae which encyst in the organs of the body cavity of fish. The life cycles of some species require the adult parasite to live in the intestine of fish-eating birds. The feces of the birds contains infective eggs or larvae. These infective stages infect waterborne snails or other small organisms. There, the parasite matures and the infected organism is eaten by fish. Heavily infected fish can die.

Human Safety: The parasites in this form are not known to infect humans that eat the affected fish. Flesh of the infected fish is not affected.

Common in oder fish throughout North America, intestinal parasites are only visible when the intestine is opened. The parasites shed eggs or larvae in the feces of the fish. The majority of parasites rob their hosts of food or use the host's blood for their own survival. Large numbers of parasites can be involved with poor immune systems in the fish affected. Large numbers can also cause physical obstruction to the intestine (uncommon).

Humans Safety: Humans eating the flesh of affected fish are not at risk of being infected. Anytime the intestines are opened during the cleaning of fish, care should be taken against contamination of the flesh by bacteria. The parasites are of minimal risk to humans.

This condition is common where gill-netting or catch-and-release fishing techniques are practiced. It is caused by an inability to quickly adjust the volume of gas the fish carries in its swim bladder (regulation of depth). On calm, warm days, the fish may suffer from sun exposure or predation by gulls as a result of floating on their backs.

Human Safety:
There is no disease agent associated with this condition.