## 1 Introduction  
Collagen is the most abundant extracellular matrix protein present in mammals, which typically has a characteristic triple-helix structure that easily enables its identification [1, 2]. This specific protein structure is stabilized by intra- and inter-chain hydrogen bonding responsible for the strong and rigid nature of most tissues, constituted by continuous repetition of the glycine-X-Y sequence, where X and Y are frequently proline and hydroxyproline amino acids [3, 4]. Hitherto, collagen has been described in humans in 28 different types, with a variation in molecular arrangement and functional properties, and accounts for 25-35% of the total protein mass, collagen being the major constituent of the dermal skin layer, connective tissues, cartilage, tendons, and bone [5, 6, 7]. Furthermore, each type of collagen has unique physicochemical properties, molecular weight, sequence, and amino acid composition, which influence the quality of the collagen [8, 9, 10, 11]. The main conventional sources of collagen for industrial use are bovine and porcine origin. Nevertheless, some religious constraints have been raised on its use and other sustainable alternatives of collagen have been appearing, including the ones resulting from the better utilization of marine byproducts as a low-cost effective form of collagen [12]. Moreover, marine collagen is associated with low immunogenicity and lack of risk of transmission of diseases or zoonoses, fewer regulatory issues, and a high potential for industrial applications [13; 14; 15]. The advances in the know-how of processes and technologies have been enabling the isolation of high-added-value products from marine byproducts such as valuable proteins and biomolecules like collagen, gelatins, and bioactive peptides [16]. Nowadays, collagen from marine origin has been extracted from different raw materials such as the fish skins of starry triggerfish (_Abalistes stellatus_) [17], Atlantic codfish (_Gadus morhua_), and salmon (_Salmo salar_) [18], the swim bladders of giant croaker (_Nibea japonica_) [19], Atlantic cod (_Gadus Morhua_) [20], and yellowfin tuna (_Thununus albacares_) [21], the arm of octopus (_Callistoctopus arakawai_) [22], shark (_Prionace glauca_) and ray (_Zeachara chilensis_ and _Bathvraja brachyqrops_) cartilage [23], from the bell and oral arms of jellyfish (_[PERSON]_) [24], and fish scales of sardines [25], to name a few. The physicochemical characteristics of collagen vary between marine species, habitats, age, and extraction methods [26]. Furthermore, collagens are frequently solubilized using an acetic acid treatment that is followed by polypeptide protonation [27; 28]. Indeed, collagen has exceptional properties such as biocompatibility [29; 30], biodegradability, low toxicity, and low antigenicity, and is a key element in wound healing [19; 31], being of utmost importance to biomedical, pharmaceutical, and cosme industries [32; 33; 34; 35; 36; 37]. In the skincare and cosmetic areas, marine collagen can be used for wound dressing [38; 39; 40], for dermal moisturizing applications as a promising ingredient in cosmetic formulations due to a good capacity to retain water [18], for an antioxidant ingredient to provide protection against UV radiation due to stimulating collagen synthesis, minimize the lipid skin degradation and photo-aging effect [41; 42; 43], or as skin-hydrating and firming agents principally following several applications [44; 45; 46]. Recently, a drink containing fish collagen hydrolyses showed an improvement in skin parameters such as hydration, wrinkles, pores, and collagen content in human skin [47], being a new application of collagen and consequently adding value to marine byproducts. This work used Greenland halibut _Reinhardtius hippoglossoides_ ([PERSON], 1793) skins as a byproduct for the extraction of valuable collagen protein and further characterization. To our knowledge, the extraction of Greenland halibut collagen and, so far, its valorization has never been reported.