Most fish are "cold-blooded", allowing their body temperatures to vary as ambient temperatures change, though some of the large active swimmers like great white shark and tuna can hold a higher core temperature. Fish are abundant in most bodies of water. They can be found in nearly all aquatic environments, from high mountain streams to the abyssal and even hadal depths of the deepest oceans. At 32,000 species, fish exhibit greater species diversity than any other group of Terran vertebrates.
Fish are an important resource for humans Union wide, especially as food. Commercial and subsistence fishers hunt fish in wild fisheries or farm them in ponds or in cages in the ocean (aquaculture). They are also caught by recreational fishers, kept as pets, raised by fishkeepers, and exhibited in public aquaria. Fish have had a role in culture through the ages, serving as deities, religious symbols, and as the subjects of art, books and movies.
While printed and vat grown fish and roe is readily available, the trend to "natural sourced" foods has not diminished and, despite these kill free alternatives, is in steady demand.
There are many fish species and fish related products traded. Fish are classified BioHaz Level 0 and can be freely traded.