A fish is any member of a group of animals that have gills and lack limbs with digits. They are generally streamlined and extract oxygen using their gills. Most fish are ectothermic or cold-blooded allowing their body temperatures to vary as ambient temperatures change although some fish such as tuna can hold a higher body temperature (Endothermic) to support high bursts of speed.
Fish are found in must bodies of water from high altitude lakes to the abyssal depths of the oceans. There are 33,100 recorded fish species.
Fish are a vital resource and food source for humans however, overfishing is depleting many species and threatening fish stocks all over the world.