Title: Alternative methods for fish grading

Author(s): Lillian Chebet
Final project
Year of publication:
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Supervisors: Hjorleifur Einarsson


This study is aimed at screening for alternative methods for fish grading through choosing appropriate quality indicators and comparing alternative methods with sensory methods using the quality index method (QIM). Whole gutted cod fish samples were stored for 2, 3, 5, 6, 7, 8, 10 and 11 days from capture and were analysed within 24 hours at the University of Akureyri. Prior to the actual analysis, a pilot analysis was carried out to determine the application and precision of the application resazurin dye, ATP meter, and combur-3 strips to measure, microbial ATP expressed in relative light units (RLU), pH, protein, and glucose concentration in fish respectively in comparison with sensory methods for fish grading using QIM. Skin swab area of 100 cm2 and gills swab, 10 mL of autoclaved water and 1 mL of resazurin were used. The results obtained indicated a wide variation in the different methods evaluated. RLU values indicated an inverse relationship with QI values, resazurin dye indicated a linear relationship with QI values, protein, glucose and pH test values indicated an inconsistent relationship with QI values and in some cases there was no relationship. However, conclusions and recommendations were made which are; QI values as expected exhibited a linear relationship with storage time; relative light units could be an appropriate method for grading fish but further research to identify appropriate volume (sample area) is recommended for better results. Resazurin dye could be a reliable and appropriate alternative method for grading fish both within and outside the laboratory, but calibration of resazurin dye colour change is highly recommended to enable estimation of the number of bacteria in the sample. pH, glucose and protein concentration seem not to be appropriate methods for grading fish due to inconsistent test values and perhaps other alternative indicators could be identified.

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