Adult population structure of Caligus rogercresseyi after pharmacological treatments

The sea lice control regulations on salmon farms in Chile require weekly monitoring of Caligus rogercresseyi populations and specifically recording the number of gravid females, mobile adult (male and female without eggs strings) and attached chalimus stages. The sea lice threshold to trigger treatment has been established to maintain the number of gravid females <3 per fish after the application of any antiparasitic treatment. However, because the non-gravid females are not considered in the count, this generates an underestimation of the real abundance of the total females on the fish and also an underestimation of the fecundity rate. This study shows that the number of females was higher than the number of males after the application of an anti-sea lice treatment, with the lowest sex ratio (1.2:1) for emamectin benzoate and the highest sex ratio (14.9:1) for azamethiphos. There were no significant differences in the proportion of females after an anti-sea lice treatment for the different products (p = 0.609) and the same for males (p = 0.864). The percentage of non-gravid females in the total females ranged from 11.2 to 51.7% and the non-gravid component of the mobile adults ranged from 15.0 to 77.6% after an anti-sea lice treatment.