Fish Lice – Causes, Diagnoses And 4 Perfect Ways To Treat

Fish Lice

Last updated on October 11th, 2022 at 03:00 am

Fish lice from the family Argulidae are branchiura crustaceans that parasitize both freshwater and marine fishes. Fish lice can pose a significant hazard to fish health, due to the fact that heavy infestation can trigger substantial morbidity and death.

In addition, fish lice are understood to be the vehicle for many other fish diseases. When we were doing rounds at our center, Fish lice was gathered from the caudal and anal fins of 3 goldfish (Carassius auratus).

These goldfish were asymptomatic, and no extra cases were noted the lice were removed manually. As quickly as any Fish lice organisms are recognized, management and treatment are suggested due to the fact that infections can spread quickly.

Presently, there are no FDA-approved drugs for the control and treatment of this parasite, however, the use of many chemicals containing organophosphates and diflubenzuron has actually proved to be successful. The screening and quarantine of inbound fish is the very best method to prevent a facility-wide fish lice infestation.

Fish lice are members of a big group of branchiura parasites that trigger and cause severe diseases in fish. The argulids are shellfishes and belong to crabs, lobsters, and shrimp.

There are roughly 100 various types of Fish lice dispersed worldwide that, depending on the types, can badly infest freshwater and saltwater fishes. The 3 most-studied types, Argulus foliaceus, Argulus japonicus, and Argulus coregoni are discovered in freshwater systems.

Infections with these are most typical in pond-raised and wild freshwater fish, especially goldfish, koi, and other cyprinids (minnows and carps); centrarchids (sunfishes) and salmonids (salmon and trout). Argulus foliaceus has actually likewise been discovered on toads and frogs.

Fish Lice Biology

Fish Lice

Fish lice are dorsoventrally flattened (i.e. it flattened from the topside to the underside), have an oval to rounded body covered by a large carapace (external protective covering), and 2 compound eyes. A thin, needle-like “stylet” situated in front of the mouth tube is used when piercing the host and assists the parasite in ingesting body fluids.

In the adult, 2 popular “suckers,” one situated on each side of the mouth and stylet, are used to connect or attach to the fish. These suckers develop from hook-like structures in more youthful phases. Hooks and spinal columns found on their appendages (“legs”) help with movement.

Older juveniles and adult Fish lice foliaceus are around 3 to 7 mm long and  2 to 4 mm wide. Females are bigger than males and can be identified by short, paired structures at their back end referred to as seminal receptacles (spermathecae), which receive sperm from the male.

Fish lice life cycle

Fish lice has a direct life process, meaning it just needs one host (the fish) to totally develop from an egg to a fully grown, replicating adult. All shellfish, consisting of Fish lice, grow and develop through a complicated series of molts (i.e., by shedding their external surface, or “exoskeleton,” which is made from a substance called chitin) and several life phases. Unlike copepod – another group of crustacean fish parasites, such as Lernaea (the anchor worm), branchiuras continue to molt occasionally even after reaching maturity.

Infauna - 2 Amazing Information You Need To Know

Some chemical control techniques eliminate the parasite by hindering the molting procedure.

While the branchiura life process averages 30 to 60 days, the real period depends upon the parasite types and the water temperature level. All life phases of both sexes are parasitic, unlike the non-parasitic male anchorworm (Lernaea), an associated shellfish copepod parasite. Fish lice adults can survive for many days off the fish host.

The adult female detaches from the fish host to lay eggs on hard surfaces and vegetation around the area after a male and the female pair mate. And after her eggs have been released, the female then goes back to the fish host.

The time needed for Fish lice eggs to hatch will differ, depending upon the types and temperature level. The eggs of fish lice hatch in 10 days at 35°C, however, they need 61 days at 15°C.

At 23°C the eggs of closely associated types, A. foliaceus, hatch in 17 days, whereas at 20°C, they hatch in 30 days. Eggs are capable of overwintering (making it through winter) up until the next spring if laid in the fall.

In many types, the very first phase larvae (called the “metanauplius”) (Figure 2) need to discover a parasitic host within 2 to 3 days of hatching or they will pass away. When connected to the fish host, juveniles go through a series of molts (11 molts or 12 “phases” in A. foliaceus) up until they reach sexual maturity, approximately 30 to 40 days after hatching. Juveniles can overwinter within the fish’s mucous.

Diseases caused by fish lice in fishes

Fish lice infestations or invasions tend to peak in the summer and fall. The lice can be seen attached to the skin, gill chamber, and mouth of a fish.

Localized swelling happens at the contact site due because of mechanical damage from spines and hooks on the stylet and appendages, and inflammation from digestive enzymes.

If the infestation is heavy, the fish lice might be seen all over the skin and fins of the fish and in the water column. Fish without noticeable lice might show non-specific indications of infestation. These consist of the area or pinpoint hemorrhages, anemia, scale and fin loss, increased mucous production, erratic swimming, sleepiness, decreased feeding, hanging at the surface (do not want to swim into the water column), and poor body condition.

Cuttlefish: Overview, Description, And Facts

Fish might “flash” or rub against the surfaces in an effort to ease inflammation or to remove the parasites. Sometimes, there might be no apparent signs of disease other than the existence of the parasite.

Fish might endure even moderate and low levels of Fish lice with very few indications of disease, localized swelling, and damage at the afflicted site might lead to secondary infections. The parasite’s high reproductive rate can rapidly intensify an infection.

Severe infestation of numerous parasites might incapacitate their host with harmful skin and decrease the fish’s capability to stabilize their internal fluids and salt levels. Secondary pathogens, such as the bacteria Aeromonas and the water mold Saprolegnia, are frequently seen simultaneously with Fish lice infestation.

Fish lice are also efficient in serving as a mechanical vector or intermediate host for numerous fish diseases. The parasite can carry and perfectly transmit spring viremia of carp a reportable viral disease of koi, common carp, and goldfish, to name a few hosts.

Aeromonas salmonicida, a crucial bacterial pathogen, has actually been separated from Fish lice, the coregoni, and experiments showed greater rates of Aeromonas infection when Fish lice are present, but direct transmission from louse to fish has actually not yet been shown. Fish lice can likewise act as the intermediate host for a number of types of nematodes (roundworms).

Fish lice diagnosis and management

Fish Lice

Older phases of Fish lice can be detected with the naked eye because of their size. The parasites are seen moving on the host or swimming in the water. The parasite can also be recognized on a wet mount of the impacted tissue. Since Fish lice might quickly leave the fish once it is disturbed or removed from the water, captured fish must be analyzed quickly.

Filtering water from the system through a great mesh net might likewise assist in catching free-swimming adults or juveniles fish lice for identification.

Juvenile and adult phases (the juvenile resembles the adult but do not have suckers) are fairly simple to identify, however, their identification ought to be confirmed by a fish health specialist.

Drug options and length of treatment for Fish lice infections ought to be considered the life process of the parasite, which differs from 30 to 60 days depending upon temperature level and type. Treatment ought to target all life phases, consisting of eggs, juvenile, and adult phases both on the fish and in the environment.

Adult parasites can be removed manually from the affected fish, however, this is unwise in lots of circumstances and is an insufficient option due to the fact that eggs, unattached juveniles, and the rest of adults will still exist in the environment. Fish can be transferred to a clean tank and treated with the proper drugs, while eggs in the initial system are removed either by cleansing and decontaminating the tank or permitting it to dry entirely.

What Are Clams? - Overview, Anatomy, Ecology And Weird Lifespan

Drying might be hard in damp locations, and at cooler temperature levels eggs can make it through much longer time durations. Optimum water quality must be kept throughout the duration of any treatments.


Many medications have actually traditionally been used for both treatment of Fish lice, however possible resistance to treatment, present accessibility, the legality of usage (specifically in food fish types), dose rates, associated expenses, and fish types’ level of sensitivities might minimize alternatives.

It is best to deal with a fish health professional. There are presently no FDA-approved drugs for the treatment and control of Fish lice. Extended immersion of an organophosphate pesticide, such as trichlorfon, which acts by interfering with the nerve system, has actually been a reliable treatment when dosed at 0.25 to 0.50 mg/L active component, Once a week for 4 treatments.

But unfortunately, Dylox® 80, the only water organophosphate 24 (c) pesticide authorized for use in Florida and a number of other states, is no longer being manufactured.

Diflubenzuron is another pesticide, which acts by disrupting the parasite’s molting (“shedding”) of the external skin (“exoskeleton”) throughout development and advancement. Diflubenzuron successfully eliminates both larva and the adult phases, however, it is a restricted-use pesticide, and applicators should follow label guidelines.

Other substances with a comparable system of action as diflubenzuron, such as lufenuron at 0.13 mg/L, have actually likewise been utilized with success. Potassium permanganate (10 mg/L for thirty minutes or 1.3 mg/L used two times over 3 days) has actually been revealed to be efficient in eliminating the adult and juvenile phases of freshwater types in a number of research studies.

Potassium permanganate is not advised for usage in marine systems. Increased salt concentration does not seem reliable for the control of Fish lice in freshwater, nor does formalin.

Emamectin benzoate is an in-feed item that has actually been revealed to experimentally manage Fish lice infections in goldfish and koi. Emamectin is licensed outside the U.S. for control of sea lice, a saltwater copepod parasite; nevertheless, in the U.S. emamectin is an FDA Investigational New Animal Drug (INAD), and for that reason, is presently not available for basic usage.

Those thinking about its usage need to register and get in touch with the manufacturer in an INAD research study. Of all the drugs noted above, just potassium permanganate (in freshwater) is legal for usage in fish meant for human consumption, and its efficiency might not be perfect.

Lernaea Cyprinacea (Anchor Worms)

There are presently no authorized items for usage in foodfish types. It is critical to know where your fish are coming from and to quarantine new fish before introducing them to your system. Possibly plagued fish must not be mixed with clean fish without proper quarantine.

Reliable management of a fish lice outbreak should consist of correct recognition of the parasite, treatment of all life phases on the fish and in the environment, and correct substance use. Drugs readily available for the treatment of Fish lice invasions are restricted, so the addition of a fish health specialist in the medical diagnosis and management will assist lessen the economic and biological effect of a Fish lice break out.

Prevention of fish lice

Fish Lice

Due to the fact of possible challenges with managing this parasite, particularly in food and pond fish, biosecurity steps ought to be set up and followed to decrease intro or transmission to other ponds, systems, or centers.

Inbound fish, particularly pond-raised or wild-caught, must be quarantined, observed, and tested in order to decrease the danger of introduction.

Fish lice outbreaks, as soon as recognized, ought to be handled quickly. The water source needs to be assessed to guarantee that is not a path for the introduction of argulid eggs. Preferably, water must be filtered or gotten from n fish lice-free and fish-free sources.

Conclusion on fish lice

Heavy invasions in fish stocks can cause massive losses. Significant breakouts in rainbow trout fisheries in the UK have actually led to overall losses.

Carp aquaculture in Russia has actually experienced invasions in which fish were covered in “numerous hundred” parasites prior to dying.

Parasites plagued 100% of the fish in a sample at a stricken carp farm in Turkey, with approximately 1000 fish lice per individual.

The fish lice will easily lay their eggs on hard items such as wood boards, and these can be gotten rid of from the water to decrease the egg load in the fishery.

A short bath in a sodium chloride solution can lower the parasite load on a fish, however, this treatment needs to be done thoroughly, since too short a period or too dilute a solution is not effective, while too long or too concentrated a bath can hurt the fish.