Sharks are a group of fish characterized by a cartilaginous skeleton, five to seven gill slits on the sides of the head, andpectoral fins that are not fused to the head. Modern sharks are classified within the clade Selachimorpha (or Selachii) and are the sister group to the rays. However, the term "shark" has also been used for extinct members of the subclassElasmobranchii outside the Selachimorpha, such as Cladoselache and Xenacanthus. Under this broader definition, the earliest known sharks date from more than 420 million years ago.
Since then, sharks have diversified into over 470 species. They range in size from the small dwarf lanternshark(Etmopterus perryi), a deep sea species of only 17 centimetres (6.7 in) in length, to the whale shark (Rhincodon typus), the largest fish in the world, which reaches approximately 12 metres (39 ft). Sharks are found in all seas and are common to depths of 2,000 metres (6,600 ft). They generally do not live in freshwater although there are a few known exceptions, such as the bull shark and the river shark, which can survive in both seawater and freshwater.] They breathe through five to seven gill slits. Sharks have a covering of dermal denticles that protects their skin from damage and parasites in addition to improving their fluid dynamics. They have several sets of replaceable teeth. Well-known species such as the great white shark, tiger shark, blue shark, mako shark, and the hammerhead shark areapex predators—organisms at the top of their underwater food chain
Tetraodontidae is a family of primarily marine and estuarine fish of the order Tetraodontiformes. The family includes many familiar species, which are variously called pufferfish, puffers, balloonfish, blowfish, bubblefish, globefish, swellfish,toadfish, toadies, honey toads, sugar toads, and sea squab. They are morphologically similar to the closely relatedporcupinefish, which have large external spines (unlike the thinner, hidden spines of Tetraodontidae, which are only visible when the fish has puffed up). The scientific name refers to the four large teeth, fused into an upper and lower plate, which are used for crushing the shells of crustaceans and mollusks, their natural prey. Pufferfish are generally believed to be the second-most poisonous vertebrates in the world, after the golden poison frog. Certain internal organs, such as liver, and sometimes the skin, contain tetrodotoxin and are highly toxic to most animals when eaten; nevertheless, the meat of some species is considered a delicacy in Japan (as 河豚, pronounced as fugu), Korea (as 복bok or 복어 bogeo ), and China (as 河豚 hétún) when prepared by specifically trained chefs who know which part is safe to eat and in what quantity. The Tetraodontidae contain at least 120 species of puffers in 19 genera. They are most diverse in the tropics, relatively uncommon in the temperate zone, and completely absent from cold waters. They are typically small to medium in size, although a few species can reach lengths of greater than 100 cm (39 in).
The paradise fish, paradisefish, or paradise gourami, Macropodus opercularis, is a species of gourami found in most types of fresh water in East Asia, ranging from the Korean Peninsula to northern Vietnam. This species can reach a length of 6.7 cm (2.6 in), though most are only about 5.5 cm (2.2 in). Paradise gouramis were one of the first ornamental fish available to western aquarium keepers, having been imported toEurope as early as the 19th century. The paradise fish is one of the more aggressive members of its family. It is more aggressive than the three spot gourami, yet less pugnacious in nature than the less commonly kept combtail.
Paradise fish are fairly combative, harassing and attacking each other, as well as potentially killing small fish. In the wild, they are predators, eating insects,invertebrates, and fish fry. The popularity of this species has waned in recent decades as much...
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