What are sea lice? - briefly
Sea lice are ectoparasitic copepods that attach to the skin, gills, or fins of marine fish, extracting mucus and blood. Infestations cause tissue damage, stress, and substantial losses in aquaculture operations.
What are sea lice? - in detail
Sea lice are marine ectoparasitic crustaceans belonging to the subclass Copepoda, primarily within the family Caligidae. These organisms attach to the skin, fins, and gills of fish, feeding on mucus, epidermal tissue, and blood. Common species affecting aquaculture include Lepeophtheirus salmonis and Caligus spp., which target salmonids and other marine fish.
The life cycle comprises eight stages: egg, two free‑swimming nauplius stages, a copepodid stage that seeks a host, two chalimus stages during which the parasite remains tethered by a frontal filament, and finally pre‑adult and adult stages that are free‑moving on the host. Development is temperature‑dependent; higher water temperatures accelerate progression, reducing the interval between generations.
Attachment causes physical lesions, osmotic imbalance, and secondary infections, leading to reduced growth, impaired immunity, and increased mortality in affected populations. In intensive salmon farming, infestations can result in substantial economic losses due to decreased harvest yields and increased treatment costs.
Control strategies include:
- Chemotherapeutics: Bath or feed‑administered compounds such as emamectin benzoate, ivermectin, and hydrogen peroxide; rotation minimizes resistance development.
- Thermal treatments: Short‑duration freshwater or warm‑water immersion dislodges parasites and halts development.
- Biological agents: Cleaner fish (e.g., wrasse, lumpfish) consume sea lice, providing a sustainable predation method.
- Selective breeding: Genetic lines with enhanced resistance or tolerance reduce susceptibility.
- Management practices: Reducing stocking density, optimizing fallowing periods, and monitoring environmental parameters lower infestation pressure.
Accurate diagnostics rely on visual inspection, microscopic identification of developmental stages, and molecular assays for species confirmation. Integrated pest management combines multiple tactics to maintain parasite levels below thresholds that threaten fish health and production efficiency.