Aquariums or fish tanks can greatly vary in size, from the small aquarium for the hobbyist, to tanks containing several million liters of water in aquarium exhibits. Freshwater aquariums are the most popular kind of aquarium due to their lower cost and ease of maintenance. Marine aquariums generally require more complex equipment to set up and maintain.
Rodents have long been the preferred animal models in biomedical research, but fish are increasingly being used as laboratory animal models. Zebrafish (Danio rerio), in particular, were originally used for development and genetic studies, but are now used for a variety of biomedical applications, such as toxicology, neurobiology, oncology etc. They offer many advantages, such as their rapid development, relative ease of care, small size and small space requirements, and ease to produce transgenic models. In addition, the embryos are transparent, which facilitates experimental manipulation and observation
In addition, fish are useful indicators of environmental quality and ecological integrity, and are used in environmental toxicity testing. For example, the fathead minnow (Pimephales promelas) is used as a biological model in aquatic toxicology studies.