133. This technique is used for production reasons to produce sterile fish which have three sets of chromosomes instead of the normal two. The process generates an embryo with two sets of maternally derived chromosomes and one set from the male parent. This is achieved by subjecting the egg to hot, cold or pressure shock just after fertilisation. Heat or pressure shock is used for trout. In combination with the female-only technique the triploid technique produces sterile female fish and is commercially advantageous. The technique can also be used for salmon.