cruel methods to kill a fish

It is considered cruel to kill a fish by the following methods:

1.flushing them alive down the toilet 

2.removing them from the water until death occurs 

3.plunging them into boiling water 

4.slowly chilling them (with or without water) (note: this method is still commonly advocated in the aquarium literature, but is now considered to cause the fish unnecessary pain.) 

5.breaking the neck, without subsequent destruction of the brain 

6.mixing caster oil + in water -> pain less death