Question

Why a spear fisherman always targets tail of the fish while fishing?

Answer 1

This is all to do with the refraction of light and real and apparent depth.

As the light from the fish leaves the water it bends away from the normal (right-angled line to the surface). This makes the fish appear to be nearer to the surface.

If the fisherman aims at the centre of the fish the spear will miss (the spear passing in front of the fish) but if they aim at where they think the tail is then they will hit the body of the fish. (All this assumes that they are standing behind the fish when they throw the spear).

Fisherman aims along the line where they think the head of the fish is and so misses the body of the fish (dotted line)

The second diagram shows the case where the fisherman aims along the line where they think the tail of the fish is and so hits the body of the fish (dotted line).