because they are adapted to the water and they cannot walk on land.
yes
No. The faster moving pelagic/surface dwelling species of fish are more likely to be streamlined.
Streamlined Bodies
gets fked up
octopus and star fish
No. Some animals( example. Puffer fish) don't depend on speed so they don't have streamlined body shape. Other fish that depends on speed to catch fish or running away from predator have streamlined body shape so that they can swim faster.
Fish, birds and snakes are a few
it helps in reducing resistance in water
Sharks, Tuna, Mackerels, and Marlins are all examples of Streamlined body shape fishes.
The streamlined shape of the penguin makes it an excellent underwater swimmer, enabling it to cut easily through the water to catch fish- it's primary food source.
Dolphins and Whales are not fish, they are mammals, so that just leaves the barracuda.
Streamlined body and large lungs are some of the adaptation of the lung fish.