Abstract

The objective of this study was to describe the formation of branchial striated muscle tissue during the Parr and Smolt ontogenetic stages ofSalmo salar in response to natural environmental challenges. To achieve this, 15 Parr and 15 .Smoltsaar alevins were analyzed. Specimens were anesthetized and euthanized using 5 % benzocaine, following established animal welfare protocols. They were subsequently fixed in 10 % formalin and processed for histological analysis using Hematoxylin-Eosin/Alcian Bluedouble staining. The regeneration blastema area and the branchial region occupied by striated musculature were quantified.Parr Inspecimens, the gills were still under development, and striated musculature at the base of the filaments had not yet formed. InSmoltcontrast,specimens exhibited a well-defined regenerative blastema, suggesting an adaptive response to environmental stressors such as hypoxia.ably,Not striated muscle fibers were observed at the base of regenerating branchial filaments, fully differentiated from the blastema. Immunohistochemical analysis confirmed that these muscle fibers were positive for the anti-Shh antibody, indicating a roleSnicfor Hedgehog signaling in their formation. These findings highlight the remarkable regenerative capacity of teleost fish, particularlyingil-associated musculature. Understanding the mechanisms underlying branchial muscle regeneration could provide valuablentoinsights i fish physiology and aquaculture practices.