Most of the seafood harvest is consumed by humans, but a significant proportion is used as fish food to farm other fish or rear farm animals. Some seafoods (i.e. kelp) are used as food for other plants (a fertilizer). In these ways, seafoods are used to produce further food for human consumption. Also, products such as fish oil and spirulina tablets are extracted from seafoods. Some seafood is fed to aquarium fish, or used to feed domestic pets such as cats. A small proportion is used in medicine, or is used industrially for nonfood purposes (e.g. leather).