Barat, J. M., Rodríguez-Barona, S., Andrés, A. & Fito, P. Influence of increasing brine concentration in the cod-salting process. J. Food Sci. 67, 1922–1925. https://doi.org/10.1111/j.1365-2621.2002.tb08747.x (2002). Himelbloom, B. H., Crapo, C., Brown, E. K., Babbitt, J. & Reppond, K. Pink salmon ( Oncorhynchus Gorbuscha) quality during ice and chilled seawater storage. J. Food Qual. 17, 197–210. https://doi.org/10.1111/j.1745-4557.1994.tb00143.x (1994). Schreiber, M. A. & Halliday, A. Uncommon among the commons? Disentangling the sustainability of the Peruvian anchovy fishery. Ecol. Soc. 18, 12 (2013). Quevedo, R., Carlos, L. G., Aguilera, J. M., & Cadoche, L. (2002). Description of food surfaces and microstructural changes using fractal image texture analysis. Journal of Food Engineering, 53, 361–371.

Sun, D. (2000). Inspecting pizza topping percentage and distribution by a computer vision method. Journal of Food Engineering, 44, 245–249. Zhang, M., De Baerdemaeker, J., & Schrevens, E. (2003). Effects of different varieties and shelf storage conditions of chicory on deteriorative color changes using digital image processing and analysis. Food Research International, 36, 669–676.Jeffriess, B. A Review of Tuna Growth Performance in Ranching and Farming Operations (ASBTIA, 2015). Tacon, A. G. J. & Metian, M. Global overview on the use of fish meal and fish oil in industrially compounded aquafeeds: trends and future prospects. Aquaculture 285, 146–158 (2008). Colombo, S. M. & Turchini, G. M. ‘Aquafeed 3.0’: creating a more resilient aquaculture industry with a circular bioeconomy framework. Rev. Aquac. 13, 1156–1158 (2021). Superchilling is a food preservation method where the temperature of fish is kept between traditional chilling and freezing 3. This slows down autolytic biochemical processes in the muscle and inhibits microbial spoilage, hence prolonging shelf life 4. One way to achieve superchilling is by storing fish in refrigerated seawater (RSW), and the practice of storing fish under chilled conditions in RSW tanks has been widely used in well-boat industries to store bulk catches of live fish. These tanks are holding systems where the chilling medium of either RSW or brine of the same salinity as seawater (3.5%) is continuously pumped through mechanical chillers. Quevedo, R., Mendoza, F., Aguilera, J., Chanona, J., & Gan, G. -L. (2008). Determination of senescent spotting in banana ( Musa cavendish) using fractal texture Fourier image. Journal of Food Science, 84, 509–515.

Aas, T. S., Ytrestøyl, T. & Åsgård, T. Utilization of feed resources in the production of Atlantic salmon ( Salmo salar) in Norway: an update for 2016. Aquac. Rep. 15, 100216 (2019).Gaarder, M. Ø, Bahuaud, D., Veiseth-Kent, E., Mørkøre, T. & Thomassen, M. S. Relevance of calpain and calpastatin activity for texture in super-chilled and ice-stored Atlantic salmon ( Salmo salar L.) fillets. Food Chem. 132, 9–17. https://doi.org/10.1016/j.foodchem.2011.09.139 (2012). Shepherd, C. & Little, D. Aquaculture-are the criticisms justified? Environmental impacts and use of resources with special reference to farming Atlantic salmon. World 4, 37–52 (2014). Schubring, R. Themal stability, texture, liquid holding capacity and colour of smoked salmon on retail level. Thermochim. Acta 445, 168–178 (2006).

There was no effect of treatment on the colour of raw fillets (L*: p = 0.478; a* p = 0.823; b*: p = 0.106). The RSW fish were slightly lighter and less yellowish in colour than iced. A common problem associated with RSW stored fish is the bleaching of fillets which may hinder its market value 10. Bleaching was not seen in the fillets, as adjacent to the findings of Erikson et al. 12 who found that continuous storage of fish in RSW did not lead to lighter fillets. By visual observation, gill colour from the RSW fish seemed to be grayer and less reddish in colour which could be a more obvious evidence of bleaching, as also reported in RSW-stored cod for 4 days 29 and RSW-stored ocean pearch for several days 30. This was further verified by the present study when the lightness observed on day 7 for the RSW fish was significatly higher ( p = 0.001; ice: 36.2 ± 3.2; RSW: 41.1 ± 3.4; control: 39.4 ± 3.2), while redness lower ( p = 0.001; ice: 18.1 ± 3.2; RSW: 13.2 ± 2.5; control: 16.0 ± 4.4) than both the iced and control fish. Nevertheless, quality of fillets from RSW stored fish are still considered highly acceptable with its shelf life surpassing traditionally iced fish 31. CIE. Survey of reference materials for testing the performance of spectrophotometers and colorimeters. Publication CIE nr. 114.1. Central bureau of the CIE, Vienna, Austria (1994). Banerjee, R. & Maheswarappa, N. B. Superchilling of muscle foods: potential alternative for chilling and freezing. Crit. Rev. Food Sci. Nutr. 59, 1256–1263. https://doi.org/10.1080/10408398.2017.1401975 (2019).Tacon, A. G. J. & Metian, M. Fishing for feed or fishing for food: increasing global competition for small pelagic forage fish. Ambio 38, 294–302 (2009). For drip loss calculation, whole fish from all groups were weighed on days 0, 2, 4 and 7. Raw fillets from the ice and RSW group were periodically weighed on t = 7, 15, 22 days while smoked fillets on t = 7, 8, 9, 16, 23, 29 days. Fillets from the control group were weighed on the last sampling day. Drip loss (%) was calculated using the formula ((m 0 − m t)/m 0) × 100, where m 0 is the initial weight (g) and m t the weight (g) on the sampling day t.

O’Sullivan, M. G., Byrne, D. V., Martens, H., Gidskehaug, L. H., Andersen, H. J., & Martens, M. (2003). Evaluation of pork colour: Prediction of visual sensory quality of meat from instrumental and computer vision methods of colour analysis. Meat Science, 65, 909–918. Kang, S. P., East, A. R., & Trujillo, F. J. (2008). Colour vision system evaluation of bicolour fruit: A case study with [`]B74¢ mango. Postharvest Biology and Technology, 49, 77–85. Digre, H. et al. Rested and stressed farmed Atlantic cod ( Gadus morhua) chilled in ice or slurry and effects on quality. J. Food Sci. 76, 89–100. https://doi.org/10.1111/j.1750-3841.2010.01956.x (2011). Texture analysis was measured by a puncture test using a Texture Analyzer TA-XT plus (Stable Micro Systems, UK) equipped with a 12.7 mm flat end cylindrical plunger to poke three consecutive punctures of each muscle sample above the mid-line of the Norwegian Quality Cut (NQC, Fig. 1b). The force (N) was recorded in a texture profile curve operated by the Texture Exponent light software ( www.stablemicrosystems.com/, Stable Micro Systems) with a 5 kg load cell at a rate of 2 mm s −1 until the probe reached 80% of the fillet height. Salt content Temperature is a main determinant in both enzyme and microbiological activity. The enzyme activity observed in RSW fish during the first 7 days is possibly explained by a lower refrigerated temperature when fish were kept in RSW, suppressing the activity. When RSW fish were kept at the same temperature conditions as iced fish afterwards, the enzyme activity increased on day 15. Although whole fish from RSW resulted in a softer texture than iced fish before they were filleted, the enzyme activity apparently does not reflect this. A plausible explanation for the softer texture of RSW fish could be due to its water and salt uptake during immersion in seawater. Contrary to this, the observed softening in iced fish was likely due to increased enzyme activity during chilled storage especially during the first 48 h. Gaarder et al. 40 stated that cathepsin B + L activity increases to a threshold until 24 h postmortem and remains stable afterwards, while Duun 2 presented that the activity was stable during ice storage, indicating that these enzymes were still active and led to softening during storage. Based on our knowledge, the enzymatic activity including other enzymatic reactions involved in postmortem softening of tissue like collagenases and calpains from fish stored in RSW has not been thoroughly explored. This could be an interesting aspect for further studies which can include fish histology to identify the development of intra- and extracellular cell structures during RSW storage.

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Storage of fish in RSW is a brining method where fish is immersed in a 3.5% salt solution. Since the surrounding brine has a higher concentration than the intracellular fluid in the muscle, this results in salt entering the muscle by diffusion, thereby increasing yield. Degree of muscle swelling depends on the salt concentration where maximum swelling and WHC occurs at a 5–6% 23, 24. Previous studies reported that brining allows proteins to retain more moisture, as lower salt concentrations causes a lower degree of protein denaturation and induces swelling of muscle fibers, leading to a higher WHC 25, 26. This occurs due to the repulsive electrostatic forces of Cl − anions weakly attached to the myofibrillar and sarcoplasmic proteins, causing protein to coagulate and entrap free water 25. At higher salt concentrations, protein denaturation increases and myofibrillar proteins lose water, causing muscle dehydration and eventually yield loss 23. Storing fish in RSW could therefore be beneficial in moisture retention and potentially give the product a better cooking yield and tenderness. Further studies such as sensory analysis could be done to examine and relate this with industries’ and consumers’ preferences. Surface appearance and texture