Early development of the ectoparasite Caligus rogercresseyi under combined salinity and temperature gradients

One of the pathogens causing the highest economic impacts on the Chilean salmon industry is the ectoparasite copepod Caligus rogercresseyi, whose abundance is strongly influenced by environmental variables (e.g. salinity and temperature). Infested fish with sea lice reduces appetite, food-conversion efficiency and increase stress level, which results in decreased growth. The skin wounds, caused by the ectoparasite feeding, leave fish exposed to secondary infections and antiparasitics treatment expenses are high. To evaluate the impact of environmental variables on the early development of C. rogercresseyi, egg strings were obtained from mature females (reared in laboratory conditions) and exposed to different combinations of salinity (14, 20, 26 and 32 PSU) and temperature (6, 9, 12, 15 and 18 degrees C). The hatching success and time, pelagic life time, survival and size of nauplius I, nauplius II and copepodid were quantified. Our results indicate that salinity and temperature have a significant effect on the hatching success of this parasite. Salinities between 26 and 32 PSU result in a hatching success of 100%, whereas lower salinities (14 PSU) reduce hatching success by 60% (at all experimental temperatures) generating an increase in mortality of these early developmental stages. A temperature reduction from 18 degrees C to 6 degrees C in culture conditions significantly extended the incubation time of C. rogercresseyi by 50%. Specifically, temperature had a higher impact on nauplius I and nauplius II larvae, increasing development times to 50 and 100 h respectively, when temperature was decreased to 6 degrees C. Although combination of salinity and temperature have a significant effect on hatching time and survival in C. rogercresseyi, the combination of these variables had no impact on the size of nauplius I, nauplius II and copepodid stage. Thus, the effects on the survival and pelagic life time of the early stage of C. rogercresseyi, might substantially affect the fitness of the species under fluctuating conditions of salinity and temperature.