Management
Individual lernaeids can be removed from the affected fish using forceps. However, the removal is not always complete; sometimes the anchor portion remains embedded. The forceps method is impractical on a large scale, and other methods are recommended. Regardless of the method used, treatment of the entire system is necessary in order to treat all the fish and to control all life stages of the parasite, including those stages that survive off the host. Adult female lernaeids can survive 30 days on a fish host and are hardier than younger life stages; therefore, treatment should continue for several weeks.
A number of methods have been used effectively to control Lernaea, but recommendations will vary depending upon the fish species and the situation. Consultation with a fish health professional is necessary to ensure legal and appropriate drug or pesticide use. It should be noted that the only available treatment regimen for Lernaea in food fish species is salt. Salt has been researched as a treatment for Lernaea with variable results. In one salinity study with L. cyprinacea, a percentage of adult females survived fairly prolonged exposure, up to 22.4 g/L seawater (ppt) for up to 6 days. At 25.6 ppt, adults were killed by day 2. On the other hand, hatching of lernaeid eggs did not occur at 8 g/L seawater, and development of younger life stages that did hatch was prevented if the parasites were exposed for at least 5–6 days at 4.8 g/L. For food fish that can tolerate the salinity, 4.8 g/L seawater for up to about 30 days is the best choice to control the parasite because other drugs and pesticides are not legal for treatment of food fish species. Because adult female lernaeids are more tolerant of salt, additional measures may be necessary to effectively break the parasite life cycle. Removing fish from the system for 7 days will break the life cycle in the tank because larval stages cannot survive without a host for this time period.
For non-food fish species, such as ornamental production or home aquarium situations, additional treatments besides salt are available. Prolonged immersion with an organophosphate such as trichlorfon is an effective treatment for ornamental fish. A 30-minute bath with 25 mg/L potassium permanganate will kill larval lernaeids, but adults may survive. Diflubenzuron (also known as Dimilin) is a pesticide that interferes with growth of the parasite and will kill molting adult and larval stages at a dose of 0.066 mg diflubenzuron/liter. (Again, if the drugs or pesticides described above are not an option, then 4.8 g/L seawater for up to about 30 days should help control the parasite as long as the fish can tolerate this salinity level. Fish can also be removed from the system for 7 days to break the lernaeid life cycle within the tank.)
Wounds resulting from an infection with Lernaea should be closely monitored, and optimal water quality should be maintained for the duration of treatment to minimize risk of secondary bacterial and fungal infection. Interestingly, there is evidence suggesting that successfully treated fish may become resistant to future infections with Lernaea.
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