Nordic Naturals introduces Omega-3 Pet in liquid form for cats and dogs. The omega-3 fatty acids EPA and DHA are derived from wild-caught, sustainable anchovies and sardines, the company reports. Omega-3 Pet can be added to food or served by itself, the company adds. The fish oil supplement comes in three bottle sizes: 2 oz. for cats and small-breed dogs, and 8 oz. and 16 oz. for medium- to very large-breed dogs and for multi-dog households.