Hatching and survival of the salmon 'gill maggot' Salmincola californiensis (Copepoda: Lernaeopodidae) reveals thermal dependence and undocumented naupliar stage.

Salmincola californiensis is a Lernaeopodid copepod parasitizing Pacific salmon and trout of the genus Oncorhynchus. Salmincola californiensis is of increasing concern in both native and introduced ranges because of its potential fish health impacts and high infection prevalence and intensity in some systems. Discrepancies in the documented life history phenology of S. californiensis with the sister species Salmincola edwardsii, as well as our laboratory observations, led us to question the existing literature. We documented a naupliar stage, thought lost for S. californiensis. In addition, we found a high degree of thermal sensitivity in egg development, with eggs developing faster under warmer conditions. Survival of copepodids was also highly dependent on temperature, with warmer conditions reducing lifespan. The longest lived copepodid survived 18 days at 4°C in stark contrast to the generally accepted <48 h survival for that life stage. We also note a consistent relationship between egg sac size and the number of eggs contained. However, egg sac sizes were highly variable. Our findings demonstrate that revisiting old assumptions for S. californiensis and related taxa will be a necessary step to improving our knowledge of the parasite life history and development that will be critical to disease management.