Common Parasites of Koi and other Pond Fish
Parasites are a common problem in pond fish such as koi and goldfish that can lead to sick and dying fish. It is important to not only quickly identify but to find appropriate treatment for your fish so that fish can quickly recover. Here is a quick overview of the types of parasites that infect pond fish.
External Parasites:
External parasites are those that reside on the surface of the skin or within the gill filaments of fish.
Clinical Signs:
- Increased mucus production on skin may make fish appear cloudy or bluish
- Pale Gills
- Respiratory Distress, gaping at the surface or near splashing water features
- Increased redness, sores or ulcers on the skin
- Flashing
- Clamped fins
- Red sores on the skin and fins
- Secondary bacterial infections can occur
Diseases with Similar Clinical Signs:
- Bacterial infections
- Poor water quality
- Trauma
Diagnosis:
It is important to identify which type of parasite is causing a fish’s problems so that correct treatment can be provided as quickly as possible. The best way to diagnose external parasites in pond fish is by having a skin scraping and gill clip performed and examined under a microscope by a veterinarian with experience in fish.
Treatment:
Various anti-parasite medications exist to treat fish, both one that go directly into the water and ones that you feed to fish. Treatment will depend on the type of parasite infesting your fish.
I
Ichthyophthirius multifiliis from a skin scrape in a koi
Types:
- Protozoa: Ich (Ichthyophthirius multifiliis), Trichodina, Chilodonella cyprini, Epistylis, Heteropolaria, Ichthyobodo necator
- Trematodes (Flukes): Skin Flukes (Gyrodactylus), Gill Flukes (Dactylogyrus)
- Crustaceans: Anchor worms (Lernaea cyprinacea), Gill Maggots (Ergasilus), Fish Lice (Argulus foliaceus)
- Freshwater Clam Larvae (Unionidae and Mutelidae species)
Internal Parasites:
Internal parasites reside within the fish’s body, either within the digestive tract or within the actual tissues of the fish.
Clinical Signs:
- Reduced growth rate
- Reduced reproductive rate
- Intestinal inflammation
- Swollen belly
- Lethargy
- Muscle loss
Diseases with Similar Clinical Signs:
- Bacterial Infection
- Poor Water Quality
- Organ Failure (i.e. Kidney Failure)
- Egg Binding
- Tumors
Diagnosis:
Diagnosis of internal parasites depends on where the parasite is living. Those that are living in the digestive tract can be diagnosed by a veterinarian examining the fish’s feces under a microscope. Internal parasites that invade tissue can be more difficult to find and often a surgical biopsy of the infected tissue or a necropsy of a recently deceased fish are necessary.
Treatment:
Just with external parasites, many different treatments exist for internal parasites as well. Your veterinarian should be able to recommend the best treatment for your fish depending on the type of parasite involved.
Parasite Prevention
The best way to prevent your fish from contracting parasites is to make sure to always quarantine new fish from your existing pond fish for at least 30 days before adding them into your pond. More information on how to quarantine your new fish please click here. It’s also good to have new fish examined by a veterinarian and checked for hidden parasites with a skin scraping and gill clip. It is not only important to make sure new fish doesn’t carry parasites that may make your fish sick, but also new plants. Make sure to get plants from reputable or known sources or from nurseries where they are not grown exposed to fish at all. All plants should be rinsed thoroughly before they are added to the pond system.
Natural Effective Algae Control for Ponds
As the water warms up and the days get longer algae problems tend to rear their ugly heads. Algae is caused by a combination of available nutrients suspended in the water column (nitrate, phosphate) and the abundance of sunlight hitting the pond surface. There are various ways to address algae blooms within a pond.
The first is to decrease the amount of available nutrients to the algae. This can be accomplished by water changes where we remove 20-30% of the pond water and replace it with fresh water, repeating this daily until the nitrates and phosphates return to close to zero. However, this can be tricky to accomplish in ponds with high stocking densities or large water volumes. A great alternative plan is to out-compete the algae for the nutrients by establishing what is commonly called a “bog filter” or a planted bog. Bog filters are not what you consider a traditional filter. Instead of using filter media or sponges, bog filters utilize live, marginal plants (plants that naturally inhabit the shorelines of waterways) to use up the nutrients before algae can. There are many different ways to incorporate a planted bog into your pond. Many can be found by Google searching “Bog Filter”. The easiest is to submerge large numbers of bog plants in basket pots filled with pea gravel in a shallow area of the pond where there is plenty of water movement and sunlight. Make sure not to place the plants too deeply into the pond. The top of root ball should just be under the water’s surface. If you purchase wa marginal plants from a garden center, rinse the potting soil off the root ball thoroughly or the soil will cause your pond water to become discolored. Even with a bog filter you should still change 20-30% of your pond water by actively removing and replacing it at least once a month.
The second way to decrease algae in your pond is to add an in-line UV sterilizer to your filter system. These fit into the plumbing as it makes its way back from the filter into the pond. These will kill the floating, suspended algae as it moves through the unit. However, if your pond is highly stocked, gets lots of light, and doesn’t have many other plants, UV sterilizers often fail when used alone.
The final way to help decrease algae blooms is to decrease the amount of sunlight hitting the pond. This can be done using either artificial or live floating plants. Often in ponds with ravenous or large numbers of Koi you will want to start with a good number of mature water lilies if you choose live plants. Pick a hardy variety that reproduces quickly and can handle some stress from fish feeding on them. A good choice is the Mexican Yellow Hardy Water Lily.
For more information on water gardening and plants we recommend the book The Encyclopedia of Water Gardening.
Further Reading
General Guide to Filtration for Freshwater Aquariums
