Introduction to Pond Fish
Illness and treatment
Regular pond maintenance and water-quality checks help keep diseases away from fish, but illnesses still occur, even in the best-kept ponds. The first sign of a problem may be a fish floating at the surface, by which time it is probably too late for effective treatment. For this reason, it is vital to set up a routine for examining fish; feeding time provides an ideal opportunity to check their appearance and behavior.
The health of pond fish is hugely influenced by environmental conditions. During spells of hot weather, for example, evaporation can significantly lower water levels, which has the effect of concentrating dissolved nitrogenous waste. At the same time, elevated temperatures drive oxygen out of the water; the combination of nitrate and oxygen stress can be fatal, especially for larger fish. Many of these problems can be avoided simply by topping off water levels regularly during the summer and incorporating a pump and filter; these improve water quality, break down waste, and increase oxygen content by creating water movement. Overstocking a pond, especially if it is not well established, places great stress on its occupants, and fish may succumb to usually benign bacteria that are present naturally in the water. Overfeeding is another common environmental problem, especially in temperate areas in the spring and fall; uneaten food decomposes in the water, encouraging populations of pathogens.
Dealing with disease
Disease-causing bacteria, fungi, and parasites may be introduced into the pond whenever it is stocked with fish or plants. Undesirable organisms can also be brought in on the bodies of animals, especially wading birds, that move from pond to pond. These can multiply and cause serious harm before their presence is detected, and eliminating them can be very difficult. A table of the most common conditions seen in pond fish, as well as treatment strategies.
If your fish are affected, you are most likely to first notice changes in their behavior and feeding patterns; a sick fish may, for example, distance itself from others or take refuge behind a plant. If disease is suspected, affected fish should immediately be removed from the pond and kept in isolation, preferably in a large aquarium (see above). Here you can inspect the body close up and check for symptoms of disease or parasite infestation. Fish lice will be visible in this environment, and you should also be able to detect gill flukes much earlier than would be possible in a pond. Treatments can be carried out in the tank itself, or in smaller baths, and the fish’s progress can be readily monitored before reintroduction to the pond.
If a fish is affected with a disease or parasite, check other fish to determine whether there is a general problem in the pond or the disease is an isolated instance. Look out, too, for secondary infections. Sometimes the entire pond needs treatment with commercial chemicals, but often it is sufficient to treat individual fish. Check all water-quality parameters before reintroducing the fish; minimizing environmental stress will help prevent recurrence of the condition.
Certain diseases, such as the rapidly spreading koi herpesvirus (KHV), are untreatable, emphasizing the importance of isolating new fish before introducing them to a pond (see p.311) and seeking professional advice if many fish become ill.
- Fish lice are crustacean parasites that feed on fish blood. They are obvious when attached to the body but also live free in the water for up to two weeks.
- Bloat, or dropsy, is a serious condition, often caused by a fungal or bacterial infection. Isolate affected fish as a precaution, but this does not normally prove highly infectious.
- Fin rot begins in the inter-fin ray membranes but spreads down the fins until it reaches the body, when it can be fatal. In extreme cases, rotten parts of fins may need to be cut off under anesthesia.
- Dying or dead fish will often float to the surface of the pond. If not spotted or attended to quickly, they are likely to be taken by bird or animal scavengers.
TREATING SICK FISH
Treatments for pond fish can be delivered to an individual or to the whole pond. Individual treatment in an isolation tank (right) or by injection (below) is preferable where bacterial, fungal, or gill problems are suspected, while whole-pond treatments are more appropriate where there is a generalized parasite problem.
- Antibiotic injections and simple surgery can be carried out by the experienced fishkeeper. Veterinarians who specialize in fish are most often consulted about koi, because of the high value of these fish.
- Dosage and duration of exposure to chemicals can be closely controlled in a treatment tank. The fish can also be removed more readily if it reacts badly to the treatment.
Always supervise children near a pond, even if you believe it to be childproof. Some poolside plants can be toxic if eaten.
Use long rubber gloves when servicing the pond, and avoid dipping your hands in pondwater. Rats can contaminate the water with their urine, which may carry Weil’s disease, a serious illness that resembles the flu in its early stages.
POISONS IN THE BACKYARD
A number of garden chemicals can be harmful to fish and other aquatic life if they enter the pond. This can occur either as the result of runoff, caused by water draining into the pond, or by the chemicals wafting on to the surface. Be particularly careful if you are using any pesticides or herbicides near the pond—whether for the garden itself or when treating pets, such as dogs, against fleas— to make sure there is no risk of contamination. Otherwise, you can quickly find that you have lost all the fish.
BACTERIAL, FUNGAL, AND VIRAL DISEASES
- Fin (tail) rot – Goldfish, especially longfinned variants, and koi – Ulceration and damage to the fins, with reddish streaking. Especially common in cold weather under poor environmental conditions. – Commercial antibacterial remedy to treat causal Flexibacter bacteria. Improve water quality.
- Septicemia – All fish, especially koi – Often begins as superficial skin damage. This spreads, creating external ulceration, reddening of the body, and lethargic behavior. – Topical wound treatment. Antibiotics are needed to deal with the bacteria on the body surface to prevent them from affecting the vital organs. Improve water quality.
- Spring viremia of carp (SVC) – Koi, goldfish, and other carp – Hemorrhaging under the skin and bloated body. Autopsy reveals liver and spleen enlarged and accumulation of fluid. – No treatment is available for this highly infectious viral disease. State/Provincial Veterinarian should be notified of a suspected outbreak. Improve water quality.
- Carp pox – Koi, goldfish, and other carp – Whitish swellings develop over the surface of the body. These may fuse together to create larger areas of swelling – It is not possible to treat this viral illness, but affected fish may recover, especially if kept in clean water to prevent secondary infection. Improve water quality
- Lymphocystis – Most prevalent in goldfish but also in koi – Isolated whitish swellings over the body surface may sometimes become enlarged and branched. – No treatment is available for this viral illness; though disfiguring, it rarely causes problems and does not spread rapidly. Improve water quality.
- Fungus – All fish – Whitish areas resembling cotton fluff evident on the fins or on the body. The fungus typically gains access at the site of an injury – Use a medicated bath for sick individuals. More general pond treatments are also available. A partial water change is likely to be beneficial.
PARASITES AND ENVIRONMENTAL CONDITIONS
- Fish lice (Argulus species) – Any fish, especially koi and goldfish – Semitransparent lice, up to 1 ⁄2 in (1 cm) long, are seen close to the base of the fins. Fish frequently rub themselves to relieve irritation.- Commercial remedy. Lice can be removed with forceps, but mechanical removal may result in infection. Improve water quality.
- Gill flukes (Dactylogyrus species – Any fish – Gill covers flare open, and fish have obvious difficulty breathing. Parasites cause irritation and excess mucus production in the gills. – Commercial remedy. Be careful when handling affected fish because respiration is compromised by the presence of these flukes.
- Anchor worm (Lernaea species) – Any fish – Crustacean parasites, just under 1 in (2.5 cm) long, hang down from the sides of the body. The parasites feed directly on the fish’s body and can cause ulcers. – Adult worms can be removed with forceps; free-swimming nauplii should be destroyed using commercial treatments added to the water.
- Leeches (annelids) – Any fish – The soft-bodied parasites attach to softer parts of the fish and suck up body fluids. Large numbers cause anemia and may spread other diseases. – Commercial remedy. Eggs are very resistant to treatment. The fish may need to be removed from the pond and the eggs destroyed using calcium hydroxide.
- White spot (Ichthyophthirius multifiliis) – Any fish – Small white spots over the body, which ulcerate and are likely to become infected. Fish rub their sides against the pond; other symptoms include lethargy and appetite loss. Treat in a salt bath or with a commercial remedy.
- Suffocated fish – Goldfish and smaller koi – Occasionally occurs in ponds used by spawning frogs. The male frog mistakenly grabs a goldfish around the head, stopping its gill movements. – Check fish regularly. Net any individual that has a frog holding on to it; this should cause the amphibian to loosen its grip. Otherwise, gently separate the frog and the fish.