A branchiura crustacean known as a fish lice belongs to the family Argulidae. They parasitize both freshwater and marine fish. The presence of fish lice poses a significant threat to fish health, since heavy infestations can cause significant illness and even death.
Fish lice are parasites that can infect freshwater fish, in particular those of the Cyprinidae family. Although they do not often cause any serious harm to the infected fish, they can lead to an outbreak of disease if their population grows large enough or if your fish are kept in unclean conditions.
It can also be transmitted from one species of fish to another if they are placed in the same tank, which means it’s important to take care when you have multiple species of fish in one tank.
Fish lice biology
There are two compound eyes on fish lice, and they have dorsoventrally flattened bodies (flattened from top to bottom), an oval or rounded body covered in an external protective coating, and a big carapace. Parasites rely on a thin, needle-like “stylet” to pierce their hosts and consume their bodily fluids in addition to mouth tubes.
The adult uses two suckers to attach to the fish, one on each side of the mouth. As young as three months of age, these suckers are already hook-like. The appendages (“legs”) of these creatures are equipped with hooks and spinal columns that assist in movement.
Fish lice foliaceus are usually between three and seven mm long and two and four mm wide as they become older. The seminal receptacles (spermathecae) at the female’s back end receive sperm from the male. Females are generally larger than males.
What causes fish lice?
There are several factors that contribute to the development of fish lice infestations. Fish are more likely to contract lice if they are in an environment that is conducive to acquiring them. Freshwater fish lice are most commonly found, but they can also be found in marine environments.
Fish lice life cycle
From the egg to a fully grown, reproducing adult, fish lice have a direct life cycle, which means they only need one host (the fish). Molts are part of the growth and development process for shellfish, such as fish lice, and they shed their external surface (or exoskeleton) as they mature.
After reaching maturity, branchiuras continue to molt occasionally, unlike copepods – another group of parasitic crustaceans that includes Lernaea (anchor worms).
By hindering the molting process, certain chemical control techniques eliminate parasites.
The branchiura life cycle generally lasts for 30 to 60 days, however, the exact period of time depends on the type of parasites and water temperature. Male anchorworms (Lernaea), an associated shellfish copepod parasite, are non-parasitic and are not parasitic at any stage of their lives. It is possible for fish lice adults to survive on their own for a number of days without a host fish.
Female adult fishes detach from their fish hosts to lay their eggs on hard surfaces and nearby vegetation after mating with males. She returns to her fish host after releasing her eggs.
There is a difference in the time a fish lice egg takes to hatch based on the type and temperature. It takes 61 days for fish lice eggs to hatch at 15°C, while they hatch in 10 days at 35°C.
In foliaceus, eggs hatch after 17 days at 23°C, while at 20°C there is a 30-day hatching period. It is possible for fall-deposited eggs to survive the winter and overwinter until the next spring.
The metanauplius larva, which emerges from the egg within two to three days of hatching, must find a parasitic host within this time frame. Approximately 30 to 40 days after hatching, juveniles of Foliaceus go through 11 molts or 12 phases of molting before reaching sexual maturity. A fish’s mucus can harbor juveniles during the winter.
Fish lice symptoms
Fish lice in an older phase can be seen with the naked eye due to their size. A parasite is seen moving on the host or swimming in the water. Wet mounts of the impacted tissue can also reveal the parasite.
In order to identify this quickly, fish should be caught and analyzed as soon as possible once disturbed or removed from the water.
It might also be possible to identify free-swimming fish lice by filtering system water through a mesh net.
A fish health specialist should be consulted to confirm the identification of juveniles and adults (the juveniles are similar to adults, but they do not have suckers).
A fish lice infection should be treated according to the parasite’s life cycle, which can vary from 30 to 60 days depending on temperature levels and types. To ensure effectiveness, treatment should cover all phases of life, including eggs, juveniles, and adults, on the fish, as well as in the environment.
While adults can be manually removed from the affected fish, this is not a wise solution in many situations and is an insufficient option since eggs, unattached juveniles, and the rest of the adults will still exist.
In order to remove eggs from the initial system, clean the tank, decontaminate it, or allow it to dry completely. After the fish are transferred to a clean tank, they are treated with the appropriate drugs.
Eggs may take longer to dry in damp areas, but they can remain fresh for a long time at cooler temperatures. During the entire treatment process, the water quality must remain optimal.
Are fish lice treatable?
Depending on the severity of the infestation, and the drugs available to you, fish lice can be treated successfully. Often, the treatment is complicated due to the lack of FDA-approved medication.
Fish lice treatment
Treatment for fish lice can be done in a variety of ways. Manual removal of lice from fish can sometimes be done by a vet, but this is dangerous to the fish and results in an incomplete removal.
Liches in other life stages cannot be removed, so they will likely remain on fishes’ skins and in tanks. Once the tank has been thoroughly disinfected, any eggs left should be removed.
Several medications are available to treat fish lice, but they have not been approved by the Food and Drug Administration. Low-dose insecticides are the best method of treating fish lice. Veterinary advice should always be sought before starting any treatment.
How long does it take to get rid of fish lice?
The severity of the fish lice infestation at the beginning of treatment will dictate how well your fish recovers from it. With appropriate treatment, fish without secondary infections can recover fully within weeks.
Fish lice prevention
It can be difficult to prevent fish lice even with safety measures. Before adding fish to an existing system, they must be screened and quarantined for four to six weeks. Freshwater plants that have been living for two weeks should also be quarantined because they may also carry lice. By doing this, you can guarantee that your current tank or pond will not be infected with diseases and parasites.