Evidence for infection influencing survival of the freshwater copepod Salmincola californiensis, a parasite of Pacific salmon and trout

Christina A. Murphy, William Gerth, Travis Neal, Kelsi Antonelli, Justin L. Sanders, Trevor Williams, Ruben‐Lee Roennfeldt, Rachel S. Crowhurst, Ivan Arismendi

During investigations involving a Lernaeopodid copepod (Salmincola californiensis) parasitic on Pacific salmon and trout, we noted occasional unusual coloration of adult female copepods collected from the wild. These females were bright blue and pink in contrast to the cream white coloration characteristic of the copepod. We also observed similar color patterns emerge under laboratory settings when copepod eggs were held for hatching. In these cases, we found consistent hatching failure of blue and pink eggs and patterns in apparent disease development that would be consistent with both vertical and horizontal transmission. Iridovirus infection was initially suspected, but bacterial infection is also plausible as evidence remains inconclusive. This apparent reduced hatching success of S. californiensis warrants further exploration as it could reduce local abundances. Given the potential importance of a disease impacting this copepod, a parasite that itself affects endangered and commercially important Pacific salmon and trout, future research would benefit from clarification of the apparent infection through additional sequencing, primer development, visualization, and exploration into specificity and transmission.