How are fish different from amphibians?
Answers
Fish
Fish were the first vertebrates to evolve before 500 million years from today. They have the highest taxonomic diversity among all the vertebrates with almost 32,000 species. They drastically vary in their size, shape, and colour. The smallest known fish, Paedocypris progenetica of Sumatra, measures only 7.9 millimetres between its two ends, while whale shark is more than 16 metres long. Fish have streamlined body with fins for locomotion through the water column. They have gills for respiration, but lungfishes have lungs also as the name indicates. Fish are entirely aquatic, while very few have adapted features to live under terrestrial conditions. These cold-blooded animals inhabit almost all the fresh and salt waters including deep, shallow, estuarine, streams, lakes… etc. The saltwater species are higher in number than the freshwater species. Fish have scales on their skin, which are colourful. These colors vary among species, and sometimes with the sex. Their lateral line is a sensory organ, on which the number of scales vary among species. However, fish provide the healthiest proteins for human without disease agents. Additionally, many people keep fish for recreational purposes as well. People believe that by watching a fish tank it would relax their minds. Therefore, the importance of fish is enormous, with their ecological role, food value, and recreational values.
Amphibians
Amphibians were the next to evolve from fish. The earliest known amphibian fossil is more than 400 million years old. Today, there are more than 6,500 species living on the Earth in all the continents including Australia, but not Antarctica. Amphibians inhabit both aquatic and terrestrial environments. Most of them go to water for fertilization and egg laying, the hatchlings start their lives in water and migrate to land if needed, to spend the adult life. During their aquatic life, amphibians look like small fishes and most people misidentify those as fish. They undergo metamorphosis from larval stage into adults with development. Amphibians have lungs for air breathing. However, their skin, oral cavity, and gills may be functional for gas exchange according to the environment that they live. Amphibians are of three body forms; Anurans have a typical frog-like body (Frogs and Toads), Caudates have a tail (Salamanders and Newts), and Gymnophions have no limbs (Caecelians). The skin does not have scales, but is moist. They are very rare in arid desert climates, but common in damp environments. Their distinctive calls are audible for human and some can identify the species and function of a particular call by listening. Amphibians mostly inhabit freshwaters than saltwater environments. However, amphibians are extremely sensitive for environmental changes, i.e. they are important as bio indicators.
Answer:
Fish and amphibians are two distinct groups of vertebrates in general. However, their living environments are sometimes similar, but amphibians could inhabit both aquatic and terrestrial environments.