It is a matter of common experience that bodies appear lighter when immersed in water or any other liquid .Similarly, when a fish is pulled out of water, it appears to be heavier in air than inside the water. Objects appear to be less heavy in water or in any liquid because the liquid or water exerts an upward force on the objects immersed in it. 
Any object immersed into the water or any liquid it experiences an upward force which is equal to the weight of the fluid displaces by it . This is called buoyant force. so the object is lighter when it is inside the water than it is outside .