This procedure is usually accomplished through chemical, thermal, or mechanical methods.
Chemical methods are primarily experimental and restricted to research laboratories. Thermal and
mechanical methods are commonly used in production facilities. Triploid fish are commercially produced by applying thermal or
pressure shocks shortly after water is added to the egg and sperm mixture. The precise timing of the second meiotic division and thus, the
application of treatment to induce triploidy, varies with the species of fish and water temperature.


** Note this is 1991 info and things may have changed somewhat.