Why do fishes in the aquarium appear nearer and bigger on surface than they really are?

The phenomenon of fishes appearing nearer and bigger on the surface of an aquarium is due to refraction of light. Refraction is the bending of light as it passes from one medium to another with a different density. In this case, light travels from water (which is denser) to air (which is less dense). As light travels from water to air, it bends away from the normal (the imaginary line perpendicular to the surface of the water). This bending of light causes the fish to appear closer to the surface than they actually are. Additionally, the fish also appears larger because the light rays that reach our eyes from the fish are bent outward, causing the fish to appear magnified. This effect is more pronounced for objects that are closer to the surface of the water.