The shift in composition of traditional Atlantic salmon diets from low fat diets rich in marine ingredients to today's high fat diets rich in plant ingredients has resulted in increased fat deposition in the fish. These nutritional changes have led to a reduced content of the healthy omega-3 fatty acids (EPA and DHA), as well as Zn levels in the feeds. All these factors increase the risk of unhealthy fat deposition. There is evidence relating an excessive fat deposition in certain body regions with a less robust fish. This might therefore contribute to the 15 to 20% mortalities found in the seawater phase of salmon life cycle. These mortalities represent an extremely important issue to both, fish welfare and the industries’ economy. In salmon, adipose tissue develops within distinct regions in the body called depots. In the present project we will focus on three of the largest depots; visceral (VAT), dermal (dAT), and dorsal subcutaneous (DSAT). In mammals, these different depots are functionally and biologically different from each other and they present different associations with health and disease. For instance, intraabdominal visceral adipose tissue is a major contributor to metabolic inflammatory risk, while subcutaneous adipose tissue may have a protective role. In addition, dermal and subcutaneous adipose tissue play a pivotal role in skin repair and regeneration and thereby have a critical role in response to wound healing. This project will gain insight into the function and physiology of the aforementioned fat depots: VAT, dAT, and DSAT. By using both, in vivo and in vitro approaches, we will be able to study their role in metabolic inflammation, skeletal deformities, and wound healing and how dietary changes can affect these processes.
Fish mortality is a major challenge for the Aquaculture industry, with an annual 14.8 % mortality rate in 2020. Important causes include fatality related to mechanical handling, such as delousing (sea-lice also often cause skin wounds), infections, as well as non-transmittable diseases. Related to the latter, adult fish may develop excess fat deposition in different fat depots which are risk factors for development of low-grade metabolic inflammation and skeletal deformities. The level of fat, plant protein, and plant oil has increased in the diet of farmed salmon and the healthy omega-3 fatty acids eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) and Zink has decreased. All these factors increase the risk of unhealthy lipid deposition in fat depots. Adipose tissue depots are complex organs, comprised of several different cell types, including mature adipocytes, preadipocytes, fibroblasts, immune cells, and adipose stem cells. Based on the anatomical distribution, adipose tissue can be classified in different types. In HealthyFat, we aim to decipher important novel mechanisms of three important fat depots, dorsal subcutaneous adipose tissue (DSAT), visceral adipose tissue (VAT), and dermal adipose tissue (dAT) and their role in metabolic inflammation, skeletal deformities, and wound healing capacity which are major contributors to A. salmon health and disease. HealthyFat will provide knowledge about different adipose tissue depot development, their heterogeneous composition and distribution, and their main metabolic pathways. The potential effects of cetoleic acid, EPA, DPA, DHA, and Zinc on the modulation of these functions will be assessed. Understanding the relationship between the different adipose depots and how changes in diet composition affect skin strength, wound healing capacity, bone tissue repair, and metabolic inflammation are important information for the aquaculture to secure fish production while mantaining fish health and welfare.