Pet food is animal feed intended for consumption by pets. Typically sold in pet stores and supermarkets, it is usually specific to the type of animal, such as dog food or cat food. Most meat used for animals is a byproduct of the human food industry, and is not regarded as "human grade". In 2019, the world pet food market was valued at US$87.08 billion and is projected to grow to US$113.2 billion by the year 2024. The pet food market is dominated by five major companies, as of 2020: Mars, Inc., Nestle Purina Petcare, J. M. Smucker, Hill's Pet Nutrition, Inc. (owned by Colgate-Palmolive), and Blue Buffalo Co. Ltd (owned by General Mills). Industry In the United States, pet-food sales in 2016 reached an all-time high of $28.23 billion. Mars is the leading company in the pet food industry, making about $17 billion annually in pet-care products. Online sales of pet food are increasing and contributing to this growth. Online sales in the US increased 15 percent in 2015. Worldwide, the compound annual growth rate of pet food purchased online was more than 25% between 2013–2018. , the U.S. leads the world in pet-food spending. Impact Given the carnivorous dietary habits of many pets (especially cats and dogs), involving the consumption of an estimated fifth of the world's meat and fish, the impact of pet-food production on carbon footprints and on climate change becomes an issue. Fish food Fish foods normally contain macronutrients, trace elements and vitamins necessary to keep captive fish in good health. Approximately 80% of fishkeeping hobbyists feed their fish exclusively prepared foods that most commonly are produced in flake, pellet or tablet form. Pelleted forms, some of which sink rapidly, are often used for larger fish or bottom-feeding species such as loaches or catfish. Some fish foods also contain additives, such as beta carotene or sex hormones, to artificially enhance the color of ornamental fish. Bird food Bird foods are used both in birdfeeders and to feed pet birds. It typically consist of a variety of seeds. However, not all birds eat seeds. Nectar (essentially sugar water) attracts hummingbirds. Cat food Cats are obligate carnivores, though most commercial cat food contains both animal and plant material supplemented with vitamins, minerals and other nutrients. Cat food is formulated to address the specific nutritional requirements of cats, in particular containing the amino acid taurine, as cats cannot