Flukes belong to the group of parasites known as consist of Monogenean trematodes. These are divided into Dactylogyrus species and Gyrodactylus species.
Dactylogyrus are basically divided into those which can affect a range of fish species or those which infest only one fish species. The type which are host species specific are by far the most common. They affect the gills of fish, and reproduce by laying eggs. The rate at which they lay eggs and hence become sources of infestation to other fish varies according to the water temperature – the higher the temperature, the faster the egg-laying, up to at least 20 eggs per hour in warm water temperatures in the range of 22 – 24ºC. These eggs on release float out from the gills into the environment, and hatch into the next, larval stage. Again the time taken to hatch depends on water temperature, but can vary between 20 days in cool water to as short as 4 days at higher temperatures. The newly hatched larvae can attach to the next host after about 4 days, and 10 days or so after that the larvae will have matured into the egg-laying stage and the cycle starts all over again. Since no intermediate host is required, this is what is known as a direct life cycle, and one infested fish has the capability of infestion large numbers within a very short time in warm conditions.
New studies have shown that although the eggs of these flukes are very resistant, one single treatment with Fluke-Solve™ can take care of any hatching larvae, so long as no major water changes are carried out for at least 4 weeks after treatment. However, just to be sure a second treatment 3 weeks after the first will make certain.
The flukes attach to the gill surfaces and feed on blood and epithelial tissue. Affected fish will have some difficulty in breathing normally owing to the interference with gill function, and will show pale gills with extended gill covers.
Not only do they cause gill damage, but the disturbance they cause to the integrity of the gill surface allows the entry of pathogenic bacteria such as Aeromonas and Flavobacterium species as well as viruses.
Gyrodactylus species are commonly known as skin flukes. Although they consist of distinct separate species from the gill flukes, both types of flukes can vary where they attach and feed on fish, so gill flukes can be found on the skin and also skin flukes may colonise the gills.
These flukes reproduce by giving birth to live offspring which can sometimes be seen within the body of the adult fluke. This means that they have the possibility to be treated with Fluke-Solve™ throughout their life cycle. Again, as with the gill flukes, Dactylogyrus, their life cycle is direct – in other words they do not need any intermediate host to complete their life cycle, which means that one adult has the potential to produce large numbers of infective offspring and so can infest large numbers of susceptible fish.
When flukes infest a fish, they attach to the skin of the fish using hooks, and cause serious irritation, which the fish responds to by scraping or flicking. This is the symptom most commonly recognised by fish keepers. However fish can cause mechanical damage to themselves by trying to rub on objects in the pond. Also the flukes by their method of attachment will cause skin damage which will in turn allow the entry of pathogenic bacteria such as Aeromonas and Flavobacterium species and possibly even viruses. Affected fish can lose their colour and become depressed since large infestations of parasites will inevtiably stress fish. Since these flukes can live in the pond without needing to be attached to fish, pond hygiene during treatment is really important since they can ‘hide’ in accumulated debris where the product may not be able to penetrate successfully. Check drains, sumps, pipework and all the various component parts of filters and make sure they are clean.
The active ingredient of Fluke-Solve™, praziquantel, is a well-researched treatment for skin and gill flukes as well as tapeworms (see below). However, pure praziquantel is difficult to dissolve in water which is why Fluke-Solve™ has been developed in a special formulation to make it easy to dissolve in a tank or pond but still efficacious against these parasites. Also it is safe for bacterial biofilters, plants and for other pond or tank life in the system.
Thanks to Bernice Brewster for the photographs.