Fish oil supplements for dogs are used therapeutically for various clinical conditions, aswell as to supply essential omega-3 fatty acids during growth and development. However, products may be variable in quality, potency, and stability. The objective of this study was to analyze 11 canine fish oil supplements from two time points (2010 and 2021) for the omega-3 fatty acids eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), polychlorinated biphenyl (PCB) arochlors, minerals, and vitamins A and D, as well as to compare their compositions to each other and their respective manufacturer labels. The methods for this investigation differed in some cases between 2010 to 2021, as testing was performed at a different laboratory, or a different method was used, or both in the case of vitamin D. One previously analyzed product was discontinued and replaced. Molybdenum, cadmium, mercury, lead, and PCBs were not detected in any samples. Other minerals were detected in some products, and concentrations were below chronic exposure limits for adult humans. EPA concentrations varied between timepoints, ranging from -66% to +723%, while DHA varied from -55% to +392%. Overall, there were 10 instances of products not meeting label claims for EPA or DHA. In all 7 instances of minimum content claims for vitamins A and D, the analyzed concentrations did not meet the claims. Overall, products were assessed to have low risk for vitamins A and D toxicity when used as recommended but cannot be considered a reliable nutritional source given the variability and inaccurate label claims.