What are fish lice? - briefly
Fish lice are parasitic crustaceans of the order Arguloida that attach to the skin, gills, and fins of freshwater and marine fish, feeding on mucus and blood. They cause irritation, stress, and can transmit secondary infections in their hosts.
What are fish lice? - in detail
Fish lice belong to the order Copepoda, subclass Siphonostomatoida, family Caligidae. They are ectoparasitic crustaceans that attach to the external surface of aquatic vertebrates, primarily fish. Adult specimens consist of a segmented body, a pair of robust antennae used for anchorage, and specialized mouthparts that pierce host tissue to extract blood, mucus, and epithelial cells.
Key biological features include:
- Direct life cycle without intermediate hosts; eggs are released into the water column and develop into free‑swimming nauplius larvae.
- Six naupliar stages followed by two copepodid stages before reaching maturity.
- Sexually dimorphic adults: females larger, capable of producing thousands of eggs per spawning event.
- Host specificity varies; some species exhibit narrow preference for a single fish species, while others infest multiple hosts across diverse habitats.
Pathological effects on fish involve:
- Mechanical damage to skin and gill epithelium, leading to lesions and impaired respiration.
- Hemorrhage and anemia caused by continuous blood feeding.
- Secondary bacterial infections facilitated by compromised integument.
- Reduced growth rates and increased mortality in heavily infested populations.
Economic relevance stems from losses in aquaculture and wild fisheries. Infestation levels correlate with decreased feed conversion efficiency and market value of affected stock. Management strategies focus on:
- Environmental control: maintaining optimal water temperature and salinity to limit parasite development.
- Chemical treatments: application of approved ectoparasitic agents such as emamectin benzoate, administered according to regulatory guidelines.
- Biological approaches: introduction of cleaner fish species that consume ectoparasites, and selective breeding for resistant host strains.
- Biosecurity measures: quarantine of new stock, regular health monitoring, and sanitation of equipment to prevent introduction and spread.
Geographic distribution of fish lice encompasses marine, brackish, and freshwater systems worldwide. Species richness peaks in temperate coastal zones where host diversity is high. Ongoing research examines genetic variation among populations, resistance mechanisms to therapeutics, and the impact of climate change on parasite prevalence.