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, hydrogen peroxide, dichlorvos and cypermethrin, on the hatch and subsequent development of egg strings from salmon lice (Lepeophtheirus salmonis) which survived the treatments. All treatments significantly reduced the hatch compared to reference egg strings (9 weeks post treatment), although hatching was significantly higher after cypermethrin treatment than for the other two treatments. Subsequent development of the larvae to nauplius and copepodid stages was also significantly reduced by all treatments, the same differences between treatments being evident as seen for the total hatch. The proportion of opaque white egg strings after treatment was closely and negatively associated with the numbers of larvae hatching and developing to the nauplius stage.