The effect of chemotherapeutic drugs used to control sea lice on the hatching viability of egg strings from Caligus rogercresseyi

• Bath treatment with antiparasitic drugs has detrimental effect on the hatching of C. rogercresseyi.
• Bath treatment with antiparasitic drugs has detrimental effect on the larvae of C. rogercresseyi.
• Abortion at hatching was higher in pigmented eggs strings than in unpigmented.

The effect of four treatments used in the control of sea lice on the fecundity rate of Caligus rogercresseyi was assessed. Samples of gravid females were collected from farmed rainbow trout in a site located in southern Chile (43°8′S, 73°35′W). Gravid females were exposed to 0.4 and 2 ppb azamethiphos, 0.2 and 1 ppb deltamethrin, 100 and 500 ppb emamectin benzoate, and 42 and 336 ppm hydrogen peroxide in separate baths. After 24 h of exposure at controlled temperature and photoperiod, the mortality of females was evaluated and the egg strings removed. Egg strings were incubated in fresh filtered seawater at 12 °C and were daily evaluated for a period of 7 days. In the deltamethrin group, a hatching of 67% and 61% of the egg strings was recorded for on the fourth day in the low and the high concentration of deltamethrin, respectively. In the emamectin benzoate group, 43% and 42% of egg strings hatched at the low and high concentrations, respectively, while the corresponding figures for azamethiphos were 44% and 50%, and for hydrogen peroxide 36% and 50%. The emerged nauplii were observed to be inactive in all exposed groups. In the control group, hatching began on the second day, and the first copepodids were seen on day seven. Even though the exposures were done for 24 h while ordinary bath treatments last for 30–60 min, the results indicate that treatments with antiparasitic products to control sea lice could have a detrimental effect on the maturation and hatching of exposed eggs strings, as well as over the survival of exposed larvae of C. rogercresseyi.