Abstract: A Power head for a fishing spear comprising a chamber to house an explosive cartridge open at one end, and a firing mechanism detachably secured to the other end of the chamber, said mechanism comprising a cylinder having two pistons slidably mounted therein and spaced apart, said first piston being connected to a piston rod projecting from the end of the cylinder remote from the chamber and said second piston being fitted with a firing pin adapted to act on a cartridge in the chamber, said cylinder being provided with a plurality of spaced ports through which water can enter and fill the space in the cylinder between the pistons, the first ports being adapted to be closed as the first piston moves along the cylinder towards the chamber and the second ports being adapted to be closed as the second piston moves in the same direction, the movement of the second piston being effected through water trapped in the cylinder between the two pistons after the first ports have been closed.