Gill flukes (Dactylogyrus) and skin flukes (Gyrodactylus) are common parasites that affect fishes. Like popular community fish, they are split between livebearers and egg layers, but that’s where the similarities end.
Despite the given names, they are both likely to be found on the gills or skin and although often found in small numbers on healthy fish, large numbers can be very debilitating. Flukes are often the cause of damage that leads to bacterial secondary infections and, being microscopic, are hard to detect. Flukes are specific to fish species, hence outbreaks are usually not across the entire tank population at once. Also, a low infestation is also usually not a problem.
Fish affected with skin flukes typically have clamped fins and increased mucus covering their body, while those affected by gill flukes present for difficulty breathing. However, it is important to note that gill flukes can infest the skin and skin flukes can infest the gills too.
If done, Cytologic examination of a sample will reveal elongate flukes that have a row of hooks on their opisthaptor. These flukes cause damage to this fish at the site where their anchors (hooks) attach; they don’t actually “feed” on the fish hence are not really parasitic.
Flukes can be livebearers or egg producers; the livebearers can reproduce at a phenomenal rate in a closed system. Warmer temperatures and poor water quality (higher nitrogen levels, organic loads) can increase the reproductive cycles of these parasites.
Formalin, salt, organophosphates, praziquantel, mebendazole, and toltrazuril have all been used to manage monogenean fluke infestations in fish.