This study looks at how low infestation loads of adult Caligus rogercresseyi and other stressors affect the physiology of Salmo salar. Experimental fish groups were with (infested) or without (control) exposure to the parasite. The parasite cohort was followed for 78 days post-infestation (dpi), and only adult lice were observed. Additional stressors were applied at 60 and 75 dpi. The analysis included measurements of fish physiology and weight. Low-level infestations by adult C. rogercresseyi for more than 50 dpi induced moderate stress in S. salar as well as a high energy demand and increased small skin mucous cells. Threshold lice loads were identified, and above those loads, a high stress response was observed. Additional stressors altered fish physiology, inducing downregulation of the cortisol response after the first stressor and upregulation after the second stressor, but infested fish responded more strongly. Parasitism by C. rogercresseyi is energetically demanding, affecting the primary and secondary responses (e.g. cortisol and glucose levels), as well as the tertiary response (fish weight).

Background: Natural M. chilensis populations dominate habitats with a steep environmental gradient, and that are characterized by abrupt changes in salinity and exposure to desiccation. Although these populations are the source of seed supplies for the Chilean mussel culture industry (annual production around 250 thousand Tons), knowledge about natural populations is scarce. Based on video transect recordings, this study carries out research into one of the principal mussel beds and its associated epibenthic community in the Reloncaví Fjord, both along cross-shore and along-shore distribution gradients.