San Francisco Bay Brand Frozen Spirulina Brine Shrimp have been gut-loaded with Spirulina algae (used as an immune system booster in commercial aquaculture operations for years) in holding tanks prior to freezing. We recommend feeding this product to your fish a couple of days prior to undergoing a stressful situation such as a big water exchange, transfer to a new aquarium, reconfiguring of plants, adding of other fish, etc. to help boost their immune system.