Lernaea species are commonly known as Anchor worms, and are freshwater crustaceans which can cause disease problems, even death, in a wide variety of fish species. They tend to cause problems in fish in summer when water temperatures are warmer and can attach to the skin, fins, gills and even the mouth. The adult females can measure almost 1 cm in length.
The life cycle is direct – in other words the parasite does not need an intermediate host but can spread directly from fish to fish.
During development the different life stages live both on and off the fish. After a male and female parasite mate, the male dies and the female bores into the host tissue, eventually using a large anchor on her anterior (“head”) end to permanently embed into the skin and muscle of the fish.
As the female matures into an adult she begins to release eggs from a pair of sacs on her posterior (“back”) end. Each released egg can hatch within 24–36 hours into juveniles called nauplii. Females are very prolific, and can produce batches of up to 250 eggs every two weeks for up to 16 weeks in warm temperatures (greater than 25°C).
Newly hatched nauplii are free-living (not parasitic) and develop through three different naupliar stages in about 4 days. At that point they moult into the first copepodid stage, become parasitic, and attach to a host, either fish or even amphibians, often on the gills. Over the next few days, the parasite develops through five different “copepodid” stages. These stages can be found on the gills as well as the skin but are not permanently embedded in the tissue. Once in the final copepodid stage, the male detaches, but the female remains parasitic, attached to the current host or moving to another fish. Adult males die within 24 hours. Higher temperatures will accelerate the whole life cycle – in one study it was found that at 29°C it was completed in 18 – 25 days.
This is a warm water parasite – the optimal temperature range for Lernaea is 26–28°C. If temperatures fall below 20°C, juvenile Lernaea are unable to complete their development, and at 14°C, females will not reproduce. However, adult females can overwinter on the fish host, producing eggs when water temperatures warm up in the spring.
The parasites cause extreme irritation to the affected fish, and can allow secondary bacterial and viral diseases to infect the fish through the skin damage they cause by burrowing in to the fish. Also in severe infestations in the gills can kill fish. Any significant numbers of Anchor worms on fish will affect their overall health, and they will lose condition and be much more susceptible to other diseases.
The parasite can be successfully treated with Lice-Solve™. Studies have demonstrated that one treatment with Lice-Solve™ for 48 hours not only killed all of the stages on the fish, including the attached females, but these dead females also detached from the fish, leaving a clean fish. Since Lice-Solve™ is used as an immersion treatment in the pond or tank water, it will also kill any free-swimming stages of the parasite making it the ideal treatment for this serious problem.
Thanks to Bernice Brewster for the photographs