Shellfish Aquaculture Improvement Act of 2018 This bill limits recovery for certain injuries sustained by an aquaculture worker if state workers' compensation is available to such individual. (An aquaculture worker is an individual employed by commercial enterprises involved in the controlled cultivation and harvest of aquatic plants and animals, including the cleaning, processing or canning of fish and fish products, the cultivation and harvesting of shellfish, and the controlled growing and harvesting of other aquatic species.)