Effects of hydrogen peroxide, dichlorvos and cypermethrin on subsequent fecundity of sea lice, Lepeophtheirus salmonis, under fish farm conditions

The effect was investigated of three topical bath treatments, namely, hydro gen peroxide, dichlorvos and cypermethrin, on the hatch and subsequent deve lopment of egg strings from salmon lice (Lepcophtheirus salmonis) which sur vived the treatments. All treatments significantly reduced the hatch compar ed to reference egg strings (9 weeks post treatment), although hatching was significantly higher after cypermethrin treatment than for the other two t reatments. Subsequent development of the larvae to nauplius and copepodid s tages was also significantly reduced by all treatments, the same difference s between treatments being evident as seen for the total hatch. The proport ion of opaque white egg strings after treatment was closely and negatively associated with the numbers of larvae hatching and developing to the naupli us stage.