Their bodies are streamline to help them swim through water quickly against water resistance (a force) . What pushes them backwards is water resistance
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Because they have gills that allows them to take in oxygen from the water.
it helps in reducing resistance in water
A streamlined shape helps an object overcome friction easily while moving through water. This design minimizes drag by allowing water to flow smoothly around the object, reducing turbulence and resistance. Examples include the shapes of fish and submarines, which are optimized for efficient movement through aquatic environments.
the smaller they are the less resistance to water and the faster they move.
Of course it does. That's why fast-swimming fish are shaped the way they are. In fact an early airplane designer won a flight contest with a wing whose cross-section was designed by splitting a trout lengthwise and tracing its shape.
Gills, fins, and scales.
thy have gills that works in a counter current action
An electric air pump oxygenates the water in an aquarium, this allows the fish in the fish tank to breath. if there was no air pump the water would lose its oxygen and the fish would drown.
The property of water that allows fish to breathe is its ability to dissolve oxygen. As water flows over the fish's gills, oxygen molecules from the water diffuse into their bloodstream, allowing them to extract oxygen for respiration.
Catfish will not outgrow their aquarium because they release hormones into the water that limit growth. This can be overcome by frequent water changes or by putting the fish in a larger tank.
A water filter helps remove waste and harmful substances from the water in a fish tank, which can improve the overall water quality. This cleaner water allows for better oxygen exchange between the water and the air, ultimately increasing oxygen levels in the fish tank.