Lernaeosis (Anchor Worm).
The causative agent is Lernaea cyprinacea, elegans, copepod crustaceans of the family Lernaeidae. These crustaceans feed on fish blood, parasitizing their skin. They are quite large, reaching 8-12 mm in length and, most importantly, having a broad, leaf-like (flattened) translucent body colored in greenish-yellow or grayish-green, which makes them poorly visible on the fish’s body.
The adult parasite has a Y-shape. Branched outgrowths are located on the head, with the help of which the parasites attach themselves to the victim’s skin. In shape, these outgrowths resemble anchor horns, which is why these animals are often called anchor worms. They penetrate the skin of fish, causing inflammation of the surrounding tissues, and affect the body musculature and gills.
Parasites enter the aquarium with live food and water from natural reservoirs. In the latter, crustaceans are widespread and reproduce most intensively during the hot season, due to which the possibility of introducing them into aquariums increases during this period. They are very dangerous, causing deep destruction, followed by secondary infection and death of the fish.
Medium and large fish, even with a sufficiently large number of adult Lernaea parasites, may look healthy. At the same time, small fish can become very weak or even die due to just one or two parasites. The disease is rare in an aquarium, mainly during the hot season. Wounds made by the crustacean can be affected by a secondary bacterial or fungal infection. This uninvited guest massively enters our tanks along with goldfish imported from Southeast Asia countries.
Symptoms: •— The sick fish sways, rubs against objects, ulcers with bright red edges are visible on the body, in which the crustacean can be seen with a magnifying glass. Tiny white-green 
or red worms in the wounds. Inflammation on the fish body, localized redness. At the site of parasite fixation, a deep ulcer, abscess, and fistula are formed. The edges of the ulcer are bright red. The tissues adjacent to it swell due to impregnation with bloody exudate. The course of the process is complicated by the penetration of microflora into the ulcers – the ulcer increases, its edges become uneven and bumpy.
The inflammatory process captures the surface layers and muscle tissue. The parasite, penetrating through the epidermis into the dermis, reaches the skeletal muscle layer. At the site of introduction, inflammation develops, which subsequently leads to the formation of a parasitic nodule. Sac-like abscesses and deep ulcers are formed, having a bright red color along the edges, less often grayish. Often these abscesses are not recognized as a copepod infestation. In the places of ulcers, the scales of the fish are raised. White rod-shaped formations on the fins. Holes on the body can be wounds left behind by external parasites. Microbes settle in the wounds.
Treatment: Sick fish are isolated so that the eggs of the crustaceans do not enter the aquarium and to prevent the spread of diseases. Parasites at the larval stage can be destroyed using Trichlorfon. New doses should be administered at weekly intervals for 4-6 weeks. Only in this way can the complete destruction of all parasites at all stages be ensured. Medicinal lotions of trypaflavine or potassium permanganate can be used. A weak solution of trypaflavine promotes rapid healing of the wound. Since parasites penetrate deeply into the host’s tissues, they remain in the fish even after treatment.
Baths with a Masoten solution at a concentration of 0.4 mg/l are used. After a day, the parasites die, but remaining in the fish’s body, they can cause severe inflammation. Baths with a solution of Table salt (8 g/l) for 2-3 weeks or hydrochloride (0.2 mg/l) for 4 days. If the host fish is large enough to withstand inevitable trauma, then adult Lernaea parasites, if there are few of them, can be removed with tweezers. The deep puncture wounds resulting from such an operation should be treated locally with an antiseptic agent – for example, mercurochrome, to avoid infection. If the infection has already started, the affected areas must be treated. Severely infected fish cannot be saved and therefore must be destroyed.
Medicines: Aquarium Pharmaceuticals General Cure; Sera Argulol; Sera Baktopur; Sera Cyprinopur; Tetra Medica General Tonic; Masoten; Trichlorfon; Methylene blue; Neguvon; Basic Violet K; Table salt; Trypaflavine; Hydrochloride;
Prevention: Water from natural sources may contain Lernaea parasites in the free-swimming stage if fish inhabit the pond or river where this water was taken. This may be the water in which live food collected in reservoirs – daphnia and bloodworms – was transported.
