A pet is an animal kept for companionship and enjoyment or a household animal, laboratory animals, working animals or sport animals, which are kept for economic reasons.
The most popular pets are noted for their loyal or playful characteristics, for their attractive appearance. Pets also generally seem to provide their owners with benefits, keeping pets has been shown to help relieve stress to those who like having animals around.
There is now a medically approved class of therapy animals, mostly dogs, that are brought to visit confined humans. Walking a dog can provide both the owner and the dog with exercise, fresh air.
A fish is any aquatic vertebrate animal that is typically ectothermic, covered with scales, and equipped with two sets of paired fins and several unpaired fins. Fish are abundant in the sea and in fresh water, with species being known from mountain streams as well as in the deepest depths of the ocean.
Food prepared from fish is also called fish, and it is an important food source for humans. They are harvested either from wild fisheries or farmed in much the same way as cattle or chickens. They are also exploited by recreational fishers, and are exhibited in public aquaria.
Fish have had a role in many cultures through the ages, ranging from deities and religious symbols to the subjects of
The term fish is most precisely used to describe any non tetrapod chordate, that has gills throughout life and has limbs.
Unlike groupings such as birds or mammals, fish are not a single clade but a paraphyletic collection of taxa, including hagfishes, sharks and rays, ray finned fishes, lungfishes. A typical fish is ectothermic, has a streamlined body that allows it to swim rapidly, extracts oxygen from the water using gills or an accessory breathing organ to enable it to breathe atmospheric oxygen, has two sets of paired fins, usually one or two dorsal fins.
Fish come in many shapes and sizes. This is a sea dragon, a close relative of the seahorse. Their leaf like appendages enable them to blend in with floating seaweed.To each of these there are exceptions.
Tuna, swordfish, and some species of sharks show some warm blooded adaptations, and are able to raise their body temperature significantly above that of the ambient water surrounding them. Streamlining and swimming performance varies from highly streamlined and rapid swimmers which are able to reach 10 20 body lengths per second through to slow but more maneuverable species such as rays that reach no more than 0.5 body lengths per second.
Many groups of freshwater fish extract oxygen from the air as well as from the water using a variety of different structures. Lungfish have paired lungs similar to those of tetrapods, gouramis have a structure called the labyrinth organ that performs a similar function, while many catfish, such as Corydoras extract oxygen via the intestine or stomach.
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