Evaluation of Thr ee Potential Methods for Preventing the Spread of the Salmon Louse, Lepeophtheirus salmonis (Kreyer, 1837)

Lepeophtheirus salmonis or salmon lice infections are one of the most prevalent parasitic infections in the salmon aquaculture industry. Salmon lice cause an estimated loss of 3% of the production of Maine's salmon industry annually. Within the State of Maine only a portion of the farm sites experience salmon lice infections on an annual basis, while some sites have never had infections of Lepeophtheirus salmonis. Because of the potential impact that salmon lice infections could mean to those areas that to date have been fiee of L. salmonis infections, there has been concern both on the part of the State and the industry to prevent any fkther spread of the parasite by farming activities. This research evaluated three potential methods for preventing salmon lice fiom developing to the infective copepodid stage. In order to evaluate the effects of chlorine, iodine and desiccation on the development of salmon lice eggs a new culture system for L. salmonis was developed at the University of Maine. The system allowed for egg strings to be raised within individual culture chambers and utilized recirculation technology. Before being cultured L. salmonis egg strings were exposed to one of eight treatments: 200 ppm of chlorine or iodine for one minute, 500 ppm of chlorine or iodine for one minute or 10 minutes, or desiccation for either four or 24 hours. Egg strings were then raised for six days after hatching in filtered natural seawater at 32 ppt salinity at 12 C. Of the three methods examined desiccation for at least four hours was the only method that prevented Lepeophtheirus salmonis fiom developing to the infective copepodid stage. Transmission electron microscopy (TEM) of the egg membrane and egg sac revealed a complex ultrastructure that would make penetration of chemical agents difficult. This research would indicate that the allowing all equipment that is transferred between farms to remain completely dry for at least four hours would be an effective method for preventing the spread of salmon lice. The use of either chlorine or iodine to prevent the spread of salmon lice is not effective.