Pond owners can actively prevent most disease problems by making sure they obtain their stock from commercial fish propagators. Maintaining good water quality and keeping feed fresh, if catfish and bluegills are being artificially fed, can also help. Signs of fish health problems are indicated by fish behavior or appearance. Infected fishes may appear sluggish, turn quickly and repeatedly in circles (flashing), or stop eating feed they have been trained to eat. Visual symptoms include the buildup of mucus on skin, emaciation, discolored areas, eroded areas or sores, swelling of the body or gills, bulging eyes, hemorrhages, cysts or tumors, or an obvious accumulation of fluid in the body cavity.
Fish diseases common to Ohio ponds pose no threat to humans who eat infected fish if the fish are cooked properly.
For example, parasites such as tapeworms can only be transmitted to humans if infected fish are eaten uncooked, or not cooked thoroughly.
Environmental factors have a tremendous influence on fish health. Maintaining a clean environment, or good water quality, reduces the susceptibility of fish to disease. Nutritional diseases are rare in fishes unless they are artificially fed. Commercially available feeds are formulated to meet the dietary requirements of a specific type of fish. Only fresh feed specifically formulated for the type of fish being fed should be used. Bagged feed should be stored in a cool & dry area to maintain freshness.
Viral. Viruses are the worst types of fish disease. They cannot be treated and may suddenly kill an entire population. Although most viruses affect only trout and salmon, viruses can be avoided by stocking only fish obtained from a fish dealer that is certified free of Channel Catfish Virus Disease (CCVD) and Golden Shiner Virus Disease (GSV). If you stock trout, you need to obtain fish certified free of Infectious Pancreatic Necrosis (IPN), Infectious Hematopoietic Necrosis (IHN), Erythrocytic Inclusion Body Syndrome (EIBS), and Viral Hemorrhagic Septicemia (VHS).
Fungal. Fungi are unavoidable and always present in ponds. Saprolegnia is a common fungal disease that affects all freshwater fish and fish eggs. Saprolegnia attacks injured or dead tissue and produces a cotton-like growth.
Bacterial. Bacteria are normally present in ponds and only become a problem when fishes become stressed. Bacteria can infect a single fish and multiply rapidly to cause a substantial fish kill in a few days or weeks. They are often identified by their damage to fish tissue since they are not visible to the naked eye.
Bacterial Disease Symptoms
Columnaris (Flexibacter columnaris)- On scaleless fish, lesions begin as small circular erosions that have a gray-blue center and red margins. On scaled fish, lesions begin at the outer margins of the fins and spread inward toward the body. It also attacks the gills of both scaleless and scaled fishes, and in advanced cases the internal organs.
General Septicemia (Aeromonas hydrophila)- Ulceration of the skin, distended abdomen, and inflamed fins and fin bases.
Bacterial Gill Disease (Flauobacteria sp., Cytophaga sp.)- Produces clubbing and discoloration of the gills.
Furunculosis (Aeromonas salmonicida) Hemorrhages in the lining of the body cavity and visceral fat, cherry-red swollen spleen, inflamed pericardium, inflamed intestine and anus, and large lesions filled with dead cells and bloody colored fluid in the muscle or skin.
Parasitic. A parasite is an organism that lives in or on another organism. Fish often have parasites attached to gills, skin, inside the gut, or as tiny grub-like worms in their muscle tissue. Most are barely visible to the naked eye and often go undetected. A few of the most common parasites are described below.
Whirling Disease (Myxobolus cerebralis) Infects trout and to a lesser extent salmon. Causes abnormal swimming behavior, darkening of the caudal fin and peduncle and skeletal deformations.
Bass Tapeworms (Proteocephalus ambloplitis) Can infect many species of freshwater fish and are commonly found in largemouth bass and smallmouth bass. Infections can reduce growth, inhibit spawning, and result in death. Humans can be infected by eating
raw or undercooked fish.
Anchor Worm (Lernea sp.) Small thread-like parasite (less than 1/2 inch long) that attaches itself to the fins and body of fish.
Attachment point often develops into a lesion which is surrounded by a white-gray patch of fungus.
(Anchors worms on catfish pictured to the right)
Ich (pronounced “ik”) (Ichthyophthirius multifilis) White “pimple-like” parasites that burrow under the skin. Individuals are normally the size of a pinhead. Fish may be covered with just a few individuals, or in severe cases parasites may be scattered all over thebody and gills.
Black Spot (Neascus sp.) Probably the most common parasite known by anglers and the easiest to detect. Small black spots (smaller than a pinhead) that appear on the fins and body. Caused by a larval fluke which burrows under the skin. May also be found in the flesh. Life cycles of this “worm” parasite usually involve a fish-eating bird and snail.
Yellow and White Grub (Clinostomum sp., Hysterbmorpha sp.) Light colored (yellow or white) grublike “worms” less than 1/4-inch long encapsulated in a cyst in the flesh. Caused by a larval fluke that burrows through the skin and into the muscle tissue. Life cycles of this “worm” parasite usually involve a fish-eating bird and snail. Often noticed when filleting largemouth bass or bluegills. The smaller white grub is found more often in catfish. Severe infestations may have up to 2,000 “worms” on a single bluegill.