AbstractThe induction of tetraploidy was attempted in three intraspecies crosses (autotetraploid) of sal‐monid: chinook salmon (Oncorhynchus tshawytscha), coho salmon (O. kisutch) and rainbow trout (Salmo gairdneri), and in the interspecies hybrid (allotetraploid) coho × Atlantic salmon (Salmo salar).Pressure treatments of 6.2 × 104kPa (9,000 psi) were applied for six minutes at intervals from 50% of the time to cleavage to beyond first cleavage. Analysis of eyed stage embryos via flow cytometry indicated two periods of tetraploid induction existed corresponding to 55–75% and 100–110% of the first cleavage interval (FCI).The effects of different pressures and the times of application were analyzed in a study with rainbow trout. Treatments of 4.8 × 104kPa (7,000 psi) for eight minutes, and 5.5 and 6.2 × 104kPa (8,000 and 9,000 psi) for four minutes, were applied at 65, 78, and 100% FCI. Tetraploids were found in the 5.5 and 6.2 × 104kPa group treatments only when applied at 65% FCI.The results indicate that, while tetraploidy is inducible in salmonids, further experimentation is necessary to discern the appropriate time and treatment for optimal tetraploid induction in ea