Lampricides

Lampricides are chemical agents used to control populations of sea lamprey (Petromyzon marinus), an anadromous parasitic fish that damages freshwater ecosystems and commercial fisheries, particularly in the Great Lakes region of North America. The primary objective of lampricide applications is to interrupt the lamprey’s life cycle by targeting the larval stage (ammocoetes) that reside in stream sediments, thereby reducing adult lamprey numbers that would otherwise attach to and feed on fish hosts.

The most widely employed lampricide is 3-trifluoromethyl‑4‑nitrophenol (TFM), a nitrophenolic compound that interferes with cellular respiration in lamprey larvae, causing rapid mortality. TFM is typically applied as a dilute aqueous solution during the early summer when larvae are most vulnerable and before they metamorphose. In some cases, a synergistic formulation known as Bayluscide (a mixture of TFM and the anticoagulant niclosamide) is used to enhance efficacy and reduce the required dosage.

Environmental considerations are central to lampricide management. Although TFM exhibits high selectivity for lamprey larvae, non‑target aquatic organisms can be affected if concentrations exceed regulatory limits. Monitoring programs track water chemistry, fish health, and downstream impacts before, during, and after treatment. Regulatory agencies, such as the U.S. Environmental Protection Agency and provincial ministries in Canada, set permissible concentration thresholds and require detailed application plans to mitigate ecological risk.

Research continues on alternative control methods, including pheromone‑based traps, genetic approaches, and biological barriers, to complement or replace chemical lampricides while preserving ecosystem integrity.