FISH IN THE SEA
 
Fish are a group of aquatic animals. They usually have long bodies covered with scales, fins, and gills. Fish are classified into three main groups: bony fish (Osteichthyes), jawless fish (Agnatha), and cartilaginous fish (Chondrichthyes). Currently, as far as we know, there are more than 33,000 species of different types of fish, making them the most diverse group of vertebrates. No one really knows how many different species of fish there are in the world; many more are
 
continuously being discovered. We may soon be able to identify more than 35,000 species or around 40,000 known species. The oldest organisms that can be classified as fish were chordates with soft bodies that first appeared during the Cambrian period. Although they did not have a true backbone, they possessed a notochord which allowed them to be more flexible than their invertebrate cousins. Fish have continued to evolve through the Paleozoic Era, diversifying into various forms.Fish are an important resource for people around the world. They are especially used for food, while commercial and recreational fishermen are engaged in catching fish or harvesting fish from aquatic farms (aquaculture). Additionally, people use fish for recreational fishing, keeping them as pets, and other activities. |
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