Among the many external crustacean pests that can afflict freshwater fish, one of the most notorious is the fish lice, scientifically known as Argulus.
These tiny yet formidable parasites can cause significant harm to fish populations, affecting their health, growth, and overall well-being.
In this article, we will delve into the causes, symptoms, and treatment of fish lice infestations, shedding light on this intriguing and important topic in aquaculture and fisheries management.
What is Fish Lice?
Fish lice are external parasitic crustaceans that infest freshwater fish. They belong to the genus Argulus and are commonly known as fish lice due to their flattened, oval-shaped bodies that resemble lice.
Fish lice attach themselves to the skin and scales of fish using their hooked appendages and feed on the blood and body fluids of their host.
They can cause irritation, inflammation, and secondary infections in fish, leading to reduced growth, decreased immunity, and even death in severe cases.
They are considered harmful parasites in aquaculture and fisheries management, and proper identification and control measures are necessary to mitigate their impact on fish populations.
What Causes Fish Lice?
Fish lice infestations can be triggered by a variety of factors, including poor water quality, overcrowding of fish, presence of infected or infested fish, and other environmental conditions that favor the survival and reproduction of the parasites.
Fish that are weakened or stressed due to poor nutrition, disease, or other factors may also be more susceptible to fish lice infestations.
Fish infested with Argulus may exhibit symptoms such as inflammation, redness, and irritation at the attachment sites, as well as increased mucus production and respiratory distress due to infestation in the gills.
Scientific Classification of Fish Lice
- Kingdom: Animalia
- Phylum: Arthropoda
- Subphylum: Crustacea
- Class: Ichthyostega
- Order: Argulida
- Family: Argulidae
- Genus: Argulus
- Species: Argulus foliaceus, A japonicaus etc.
Types of Argulus Species
While they have some similarities in their general characteristics, such as their flattened and oval-shaped bodies, they also have distinguishing features that set them apart from each other.
Here are some typical and identifying characteristics of the given Argulus species:
Argulus foliaceus
This species has a translucent body with a dark, leaf-like appearance due to its heavily pigmented exoskeleton. It has two large, compound eyes and a pair of branched antennae at the front of its body. Its body is covered in tiny spines.
Argulus japonicus
This species has a yellowish-brown body with a broad and rounded carapace that covers its entire body, except for its tail. It has two large, compound eyes and a pair of branched antennae. Its carapace is covered in small, rounded tubercles.
Argulus niger: This species has a dark brown to black body with a rounded carapace that covers its anterior portion. It has two large, compound eyes and a pair of branched antennae. Its carapace is covered in small, rounded tubercles.
Argulus nobilis
This species has a translucent body with a broad, rounded carapace that covers its entire body. It has two large, compound eyes and a pair of branched antennae. Its carapace is covered in small, rounded tubercles, and its tail is elongated and pointed.
Argulus mugili
This species has a yellowish-brown body with a narrow and elongated carapace that covers its anterior portion. It has two large, compound eyes and a pair of branched antennae. Its carapace is covered in small, rounded tubercles, and its tail is elongated and pointed.
Argulus nativus
This species has a translucent body with a broad and rounded carapace that covers its entire body. It has two large, compound eyes and a pair of branched antennae. Its carapace is covered in small, rounded tubercles, and its tail is short and rounded.
Argulus melita
This species has a yellowish-brown body with a broad and rounded carapace that covers its entire body. It has two large, compound eyes and a pair of branched antennae. Its carapace is covered in small, rounded tubercles, and its tail is elongated and pointed.
Argulus ambystoma
This species has a translucent body with a narrow and elongated carapace that covers its anterior portion. It has two large, compound eyes and a pair of branched antennae. Its carapace is covered in small, rounded tubercles, and its tail is elongated and pointed.
Argulus megalops
This species has a translucent body with a broad and rounded carapace that covers its entire body. It has two large, compound eyes and a pair of branched antennae. Its carapace is covered in small, rounded tubercles, and its tail is elongated and pointed.
Morphology of Argulus foliaceus
Argulus foliaceus is known as a fish louse, which is a crustacean ectoparasite. As a crustacean, the body of Argulus foliaceus consists of three parts. These are:
- Head
- Thorax
- Abdomen
The body of Argulus foliaceus is flattened with an oval or rounded carapace. It is 5-10mm in size and it can be seen with the naked eye.
Head
The head is covered with a flattened carapace. There present eyes, suckers, maxillae, antennae, and proboscis.
It has two compound eyes for the detection of the host. It has two suckers to attach to the host.
Two pairs of maxillae present have hooks and spines. There are also antennas present in their heads.
Between two eyes, there presents a hollow preoral sting or proboscis by which the parasite feeds on the blood of its host.
Thorax
The thorax of the parasite has four segments, each segment bears a pair of legs. As the parasite is freely moveable, the legs use it for walking.
Abdomen
The abdomen of the parasite is a bilobed segment. The female has a visible pair of spermatheca and the male has one on their posterior end.
Argulus has a large ventral sucker, which it uses to attach itself to the host’s body.
The sucker is equipped with muscular and adhesive tissues that allow the parasite to maintain a firm grip on the host.
Argulus is hermaphroditic, meaning that it has both male and female reproductive organs. The reproductive organs are located in the posterior part of the body.
Life Cycle of Argulus foliaceus
Argulus is a louse-like parasite having a flat body generally called the fish louse. One of the most widespread crustacean ectoparasites of freshwater fish in the world.
The adult female parasite leaves the host to lay eggs. then it lays sticky eggs on the submerged vegetation, rocks, sticks, etc.
The female dies after spawning. The nauplius, metanauplius and in some species the 1st copepod stages develop within the eggs and hatch as metanauplii or copepods.
Other development stages are 2nd to 7th copepodid and finally adult.
All free-living stages are parasitic to fish.
The minimum period required for life cycle completion varies from 3-6 weeks.
Geographical Distribution of Argulus foliaceus
Argulus foliaceus is mainly a freshwater fish ectoparasite but it also can see in marine or brackish water.
It is found in temperate regions of the world. Mainly this parasite is seen in Europe, Central Asia, and North America.
- Argulus foliaceus (Cyprinidae, Salmonidae, Gobiidae, Gasterosteidae, Acipenseridae, frogs, toads)
- A. coregoni (Salmonides, Cyprinids)
- A. japonicus (Goldfish, Cyprinids)
- A. alosae (estuarine environment) Cultured salmon and trout
- Dolops spp. (Oreochromis, Clarias sp.)
Fish Lice Causing Signs and Symptoms
Become Weak: To attack the parasite, the fish faces problems in swimming because it has a physical injury. At this time, the fish looks slim, weak and sluggish. The fish becomes unfit for breeding.
Haemorrhage: The attacked fish appears to have a small haemorrhage and a reddish point from the pelvic fin to the anal fin.
Skin Irritation: It causes skin irritation by increasing mucus production over the body surface.
Increasing Secondary Infection: There are also seen skin lesions that occur as secondary infections by bacteria for the damaging effect of the suckers and proboscis.
Anemia and Death: The secondary infection causes Anemia. The small and young fish may cause death from the parasite attack.
Diagnosis
Non-specific signs of infestation including
- Spot or pinpoint haemorrhage
- Anaemia
- Fin & scale loss
- Increased mucus production
- Lethargy
- Erratic swimming
- Poor body condition
- Skin scrapings
- Gill biopsies
Prevention of Argulus foliaceus
For the prevention of Argulus foliaceus, we don’t allow the parasite into the fish habitat and take necessary steps to protect from them. These are:
Quarantine of Incoming Fish
The best way to avoid an Argulus infestation is through good biosecurity, such as screening and quarantine of arriving fish and constant monitoring of all fish.
Incoming fish, including wild-caught or pond-raised stock, should be quarantined, monitored, and sampled to minimize the risk of introduction.
To avoid the infestation of Argulus foliaceus, before releasing the fish, they need to be quarantined to prevent the parasites for 3 weeks in a separate place. The method keeps the fish free from the parasite.
Drying Pond
If the waterbody has parasites before releasing new fish, the pond needs to dry to remove the parasite and kill the parasite habitat. By this method, the fish are free from the parasite.
Monitoring The Fish
We need to monitor the fish in the waterbody so that they aren’t attacked by the parasite. If we can see any signs in the fish of attacking the parasites, we must start treatment to prevent them.
Need Good Water Quality
To prevent parasite infestation we should maintain good water quality. The polluted water creates more stress on the fish and the fish are attacked by the parasites very easily. To prevent the parasite, they need good water quality.
Argulus outbreaks, once recognized, should be handled quickly. Source water should be evaluated, and examined to ensure that it does not contain pathways for the introduction of Argulus eggs.
Ideally, water should be filtered or obtained through a fly fishing source that’s Argulus free.
Fish Lice Treatment
There are two types of prevention methods for Argulus foliaceus. These are:
Manual Treatment: Use hard substrates in pond water for attachment of eggs of Argulus foliaceus.Remove it and get sun-dried to kill the eggs.
Chemical Treatment: BHC (Benzene Hexachloride):Bath treatment at .0013-.0017 ppm. But it is toxic to man and it is restricted to use in some countries.
- Pyrethrum: Bath treatment at 20-100 ppm for 50 minutes and for 10 ppm for 3 minutes.
- Malathion:0.25-.5 ppm, 3-4 times at weekly intervals, and dip treatment in 1% malathion.
- Baytex: Bath treatment at 0.12 ppm repeated twice at an interval of three weeks.
- Dipterex: Bath treatment at 0.25ppm twice weekly
- Potassium Permanganate:10 ppm concentration for 5 hours.
- Formalin: Bath treatment at 250 ppm for 1 hour
- Salt: Bath treatment for 5 to 10 minutes at 2.5-3%.
Economic Importance of Argulus
Argulus is generally considered to be a nuisance and a potential threat to fish health and production in aquaculture facilities.
They can cause significant damage to fish tissues, which can lead to secondary bacterial infections and reduce fish growth and survival rates.
Argulus is generally considered to be a negative factor in aquaculture and has no significant economic importance.
FAQs
What is sea lice on fish?
Sea lice on fish are actually not lice, but rather a common term used to refer to parasitic copepods that infest fish in marine environments.
These copepods, which are also known as Lepeophtheirus or Caligus, are small crustaceans that attach themselves to the skin, fins, and gills of fish, where they feed on blood and tissues.
Sea lice can cause irritation, damage to the fish’s skin and gills, and in severe cases, can lead to secondary infections or other health issues for the fish.
Sea lice are a common problem in aquaculture, particularly in salmon farming, where they can spread quickly among fish in densely packed fish pens.
Can fish lice live out of water?
No, fish lice are parasitic crustaceans that require a host fish and cannot live out of water.
Fish lice have specialized structures that allow them to attach to fish skin and remain there, even during brief periods of low water or exposure to air.
However, they cannot survive for extended periods outside of water, as they rely on their fish host for nutrients and oxygen.
Is fish lice is harmful to humans?
Fish lice are small parasitic insects that attach themselves to the body of fish but do not affect humans as well.
References
- Book Fish Parasitology by Dr. Kirtunia Juran Chandra
- Pasternak, A. F., Mikheev, V. N., & Valtonen, E. T. (2000, January). Life history characteristics of Argulus foliaceus L. (Crustacea: Branchiura) populations in Central Finland. In Annales Zoologici Fennici (pp. 25-35).
- Mikheev, V. N., Valtonen, E. T., & Rintamaki-Kinnunen, P. (1998). Host searching in Argulus foliaceus L. (Crustacea: Branchiura): the role of vision and selectivity. Parasitology, 116 (5), 425-430.
- Bower-Shore, C. (1940). An investigation of the common fish louse, Argulus foliaceus (Linn.). Parasitology, 32(4), 361-371.
- Mikheev, V. N., Pasternak, A. F., & Valtonen, E. T. (2015). Behavioural adaptations of argulus parasites (Crustacea: Branchiura) to major challenges in their life cycle. Parasites & Vectors
- Moller, O. S. (2012). Argulus foliaceus. In Fish parasites: pathobiology and protection (pp. 327-336). Wallingford UK: CABI.
- Everts, L., & Avenant-Oldewage, A. (2009). First record of Argulus foregone: a fish ectoparasitic crustacean from Malaysia and additional notes on the morphology. Malaysian Applied Biology, 38 (2), 61-71.
- Mousavi, H. E., Behtash, F., Rostami-Bashman, M., Mirzargar, S. S., Shayan, P., & Rahmati-holasoo, H. (2011). Study of Argulus spp. infestation rate in Goldfish, Carassius auratus (Linnaeus, 1758) in Iran. Human and Veterinary Medicine, 3 (3), 198-204.
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