Fish are susceptible to a number of different diseases that both pond and aquarium owners must be aware of. The six most common fish problems include anchor worms, bacteria, fish lice, fungus, skin parasites and viruses. Each of these ailments is a threat to your fish; many of which are contagious and will spread with ease.
Anchor worms often wind up in ponds and aquariums as a result of irresponsible owners who buy new fish and then introduce them without taking the time to quarantine. Despite the name, anchor worms are actually miniature crustaceans that will embed themselves within the skin of the fish and then infiltrate their muscles. The anchor worms will then lay eggs and release them, which causes further damage. White or green threads may appear on the skin of the fish, as well as increased inflammation. The parasites may need to be removed physically or washed with iodine antiseptic.
Fish are vulnerable to many types of bacteria, but one of the most common is those that cause fin or tail rot. A gradual deterioration of the fin will occur overtime, and may become white in color. The overall color of the fish may also fade. Bacterial infection often occurs in fish that are injured, as their open wounds make it easier for enter.
Fish that are afflicted with lice will often appear restless or agitated. Reddish spots may also be present on them, which is a sign of inflammation. Fish lice are similar to anchor worms in that it usually results from owners adding new fish into a pond that were not properly quarantined. Lice will move from one fish to the next, transmitting both viruses and bacteria, so they can become a serious issue. Treatments include washing the wounds with iodine antiseptic or placing freshwater fish inside a seawater bath until the removal of the parasite.
Fish that have fungus will display a white or grayish growth on their fin or skin. This fungus will continue gradually eating away at them until they die. Fish that develop fungus will typically already be in a state of poor health, usually due to injuries, bacteria or parasites. Antibiotics and fungicide are the most common treatments for this condition.
The two most common skin parasites which damage fish are Gyrodactylus and Dactylogyrus. They appear in the form of small flatworms, and fish that are infected with them will display sores, hemorrhages, ulcers and may become pale in color. It is important to diagnose and treat skin parasite as soon as possible or they will rapidly kill your fish. Treatment will usually come in the form of medicated water combined with praziquantel or formalin.
There are many viruses which fish are vulnerable to, with the deadliest being hemorrhagic septicemia. As is the case with viruses in general, there are no cures. Fish with this disease will display bulging eyes and the hemorrhaging of their internal organs. Open sources may also be present. This virus results from new fish being brought into an aquarium or pond without being quarantined.