Title: Application of Quality Index Method (QIM) scheme for sub-chilled farmed Atlantic salmon (Salmo salar).

The quality of fresh fish is a concern for both the fishing industry and consumers in Sri Lanka due to insufficient cooling practices and limited quality inspection. Sensory evaluation plays an important role in assessing fish freshness and supporting quality control. This study evaluated quality changes and shelf life of gutted farmed Atlantic salmon (Salmo salar) stored under sub-chilled (SUBC) and ice-chilled (ICEC) conditions and assessed whether modifications to the Quality Index Method (QIM) scheme are required for sub-chilled salmon. A total of 54 salmon (average weight 4.42 ± 0.73 kg) were divided into two groups (n = 27 each). The SUBC group was stored in ice at -2°C to 0°C until day 16 and then at 0°C to 4°C until day 23, while the ICEC group was stored at 0°C to 4°C throughout the 23-day period. Three fish from each group were sampled on nine storage days (1, 4, 8, 11, 14, 16, 18, 21, and 23). Sensory quality of whole fish was assessed using QIM, cooked samples were evaluated using Generic Descriptive Analysis (GDA), and microbial quality was determined by Total Viable Counts (TVC). Temperature loggers monitored storage conditions throughout the experiment. QIM results showed that quality index scores increased linearly with storage time in both groups. Scores for skin odour, skin texture, eye form, gill mucus, blood in the abdomen, and abdomen odour were similar between treatments. However, SUBC salmon consistently received higher scores for eye pupil and eye form attributes, while ICEC salmon showed higher scores for skin mucus and gill colour after day 16. GDA indicated a decline in freshness characteristics over time, but no spoilage attributes were detected. The only significant sensory difference was observed on day 23, when SUBC salmon displayed a fresher flavour than ICEC salmon. TVC remained within acceptable limits in SUBC salmon, whereas ICEC salmon reached unacceptable microbial levels on days 21 and 23. The results indicate that gutted farmed Atlantic salmon stored under sub-chilled conditions have a shelf life exceeding 23 days in ice storage, while conventionally iced salmon exhibit a shorter shelf life. No adjustment of the QIM scheme was considered necessary for sub-chilled salmon.