Intestinal physiology in atlantic salmonpreparatory changes during smolting and after seawater entry

Abstract

The intestinal physiology of teleost fishes is complex, and multiple factors contribute to an optimal osmoregulatory function. This complexity is particularly pronounced in migratory species that experience variations in environmental salinity. Consequently, this thesis employed a multifactorial approach, considering biological and environmental factors that may contribute to the development of hypo-osmoregulatory capacity in the intestine of Atlantic salmon during the parr-smolt transformation (smolting or smoltification) that precedes migration of juveniles to the ocean. Utilizing an integrative approach, the work primarily aimed to investigate the development of the mechanisms associated with Na+ and Cl- movement across the intestinal epithelium, crucial for water absorption in the dehydrating environment of SW. For this purpose, both aquaculture and natural on-growing conditions were recreated. The results suggest a critical role of the photoperiodic cue in developing the intestinal hypo-osmoregulatory capacity and highlight cortisol as a crucial modulator of the osmoregulatory function in the intestine of Atlantic salmon. The intestinal HCO3- secretion cascade pathway, previously overlooked in the physiology of this species, has also been investigated. Novel results were obtained, including evidence about the regulatory action mediated by cortisol on this pathway. A clear anterior-to-posterior specialization of the intestine also emerged in the life stages examined in this thesis (parr, smolt, and post-smolt). Furthermore, the results offer evidence of a secretory pathway in the intestine of Atlantic salmon acclimated to SW. Overall, the findings presented in this thesis provide new insights into the intestinal physiology of Atlantic salmon and highlight the intestinal function as a potential tool for aquaculture. A more precise evaluation of the hypo-osmoregulatory capacity in smolts would undoubtedly be advantageous for optimizing the production, with economic, social, and environmental implications.