The entire animal kingdom can be bifurcated into two broad categories namely; vertebrates and invertebrates. Vertebrates are characterized by the presence of a vertebral column or backbone. These include mammals, fish, reptiles, birds and amphibians. Fish live in water and have gills that aid in breathing in aquatic conditions. Amongst the many adaptations that nature has provided this vertebrate to survive in water is its streamlined body. This shape helps it to cut across the water, thereby aiding in swimming.
Varied types of fish can survive in any water forms across the world. Some can even survive in waters that have temperatures below zero degrees Celsius. Amongst the 25,000 diverse varieties of fish in the world, the size varies from 8 mm to 45 feet.
Fish can be broadly categorized on the basis of the type of water they are found to originate in. One of the categories is formed by the tropical fish. Such type of fish can survive in fresh or salt water. However, one of the most vital requisites for its sustenance is warm or tropical medium temperature.
Tropical fish are most commonly kept as pet fish owing to their magnificent colors. Some of the fish in this category include angelfish, algae eater, dragon fish and archerfish. Coldwater fish need fresh or salty water at low temperatures for their survival. The optimum temperature condition for this variety is temperature less than twenty degrees Celsius. In comparison to the tropical fish, this variety projects slow growth pattern but is known to have a longer life expectancy. Some examples of coldwater fish are goldfish, koi, rosy barb and guppy. Freshwater fish thrive in the freshwaters of rivers and streams. This category includes African butter catfish, clown barb, black ghost knife and bala shark.
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