Argulus, Lernea, Ergasilus, Dactylogyrus, Gyrodactylus
Early warning signs include scratching or flashing on pond walls or other objects. The fish may jump from the water to try to dislodge these large parasites. Some or all fish will show decreased activity and huddling together and then appear to swim in an irritated manner accompanied with scratching. The fish will continue to eat until the advanced stages of infestation. Red veins in the skin are often observed. Sores can develop in scattered patches as the parasites erode skin tissue; secondary bacterial infection may follow. Always test your pond water for ammonia, nitrite and dissolved oxygen levels as similar symptoms may be confusing. Argulus and Lernea are large enough to be seen with the naked eye. Argulus (fish lice) may be seen on the skin and fins as a clear gelatinous disc-shaped bug measuring up to 0.4in (10mm). The legs and eye spots can often be observed. Lernea (anchor worm) are elongate parasites easily seen on the skin measuring up to 0.8in (20mm) long with two egg sacs at the posterior end. Gyrodactylus (skin flukes) are not easily identified being a very small parasite only 0.02-0.04in (0.5-1mm) long and will cause a greyish-white film of mucus on the body. This can be confused with a protozoan infection, microscope examination may be necessary. Ergasilus (gill maggots) will appear as grayish black and white parasites several millimeters long infesting the gills. Dactylogyrus (gill flukes) will appear on the gill filaments as tiny dark spots 0.04-0.08in (1-2mm) long.
With trematode/crustacean type infestations, the fish continue to feed but will actively scratch themselves and swim in an irritated manner. With protozoan type infestations the fish will become lethargic, refuse food, and appear to have a white sliminess to the body and fins. Determine the difference between trematode/crustacean infestations and protozoan infestations; medications are specific.
Crustaceans and flukes can be introduced with new fish and plants. Quarantine is suggested for 3-4 weeks. The life cycle of these parasites is temperature dependent. Temperatures below 10º Celsius (50º F) do not generally produce epizootics since the life cycle may last longer than 100 days. Between 60º and 70º F the life cycles may take 3 to 4 weeks. Temperatures between 70º and 80º F may last 2 to 3 weeks. The eggs of these parasites will accumulate in organic debris in the pond and also within the filter media. Keep the entire pond system clean and backwash your filter to reduce eggs. Poor water quality or stress will weaken the fishes immune system and promote proliferation of parasites. However, the crustaceans and flukes can be eradicated completely with proper pond treatment and quarantine procedures.
Trichlorfon is the treatment of choice for crustaceans. Synonyms for Trichlorfon are Dylox, Dipterex, Masoten, Mertrifonate, Lifebearer. A complete treatment program will require 5 applications of the correct dose of Trichlorfon. The therapeutic dose is between 0.25 PPM to 0.75 PPM. Ponds with pH of 7 to 7.5 will use the 0.25ppm dose. Use a treatment level of 0.50 PPM with pH between 7.5 and 8.0. When the pH is above 8.0 Trichlorfon will break down more quickly and require a dose closer to 0.75ppm. Sunlight and warmer water may also break down the medication more quickly.
Treatment is temperature dependent
When temperatures are above 80º F (27º C), treat once every 3 to 4 days for a total treatment time of 20 days. When temperatures are between 70º and 80º F (21º and 27º C), treat once every 4 to 5 days for a total treatment time of 25 days. Between 60º and 70º F (15º and 21º C), treatments will be 7 days apart for 35 days total. Between 50º and 60º F (10º and 15º C), the life cycle may last up to 2 months and will require treatment every 10 to 14 days. Below 50º the life cycle will be so long that treatment is not practical. Keep the pond and filter clean and wait for temperatures to warm up since the fish are not likely to be in danger with a slight infestation. Trichlorfon will kill most of the adult stages of fish lice and so give relief to your fish within a few days. The adult stage of anchorworm must be removed manually with tweezers and a dab of mercurochrome. Trichlorfon does not kill any parasite eggs but will kill the free swimming infective stage of all these crustaceans.
Fish which are obviously weak and heavily parasitized may not survive, however a FORMALIN BATH may help kill the infective adult stage more quickly. Use Formalin 3 (Kordon) at a concentration of 200 PPM for 50 min. as a bath in a separate container. Aerate this bath for 15 min. prior to immersing the fish and during treatment. Successive treatments may be necessary. Remove fish at first signs of distress. Do not use a Formalin bath on any fish with open sores as the Formalin could enter the body of the fish and kill it. Potassium permanganate has been used for crustaceans and flukes as a bath at the dose of 5 to 10 PPM for 1 hour; in the pond treatment of 1 to 5 PPM for an indefinite period. Dosage of Potassium permanganate is dependent on the organic load in the pond. Clean ponds use a low dose, dirty ponds and water gardens require a high dose. Always be cautious using any medication in your pond.
A SPECIAL NOTE ABOUT MONOGENETIC FLUKES
Skin and gill flukes are acquiring immunity to the standard treatments. A 200 PPM Formalin bath for 50 minutes may be of assistance. Alternatively, a salt bath at 2.0% (5 tablespoons per gallon) for 10 to 15 minutes can also work. However, depending on the severity of infestation and the number of fish affected, Fluke Tabs may be the best drug to use.
If you are using the correct method and dose of Trichlorfon and the fish do not respond within 3 to 5 days you may have misdiagnosed the parasite. Try the Paracide Green treatment for protozoan infestations.