Comparative study of heat shock and pressure shock for triploidy induction in rainbow trout (Oncorhynchus mykiss)

The study was aimed to explore the effective physical treatment for successful triploidyinduction to take the advantage of improving growth in coldwater aquaculture candidatefish, rainbow trout Oncorhynchus mykiss. Comparison was made between two commonphysical treatments viz.,, heat shock and pressure shock to prevent the extrusion of secondpolar body in newly fertilised eggs. Heat shock was given on the fertilised eggs at threetemperature levels viz., 26, 28 and 30ºC with four exposure timings of 5, 8, 10 and 12 min.Pressure shock was applied at three different levels of pressure i.e 9000, 9500 and 10000 psifor 3 different exposure times of 3, 5 and 7 min. Poidy verification of the treated eggs wasdone by counting the chromosome number in karyotyping. Results of the field operationsreflected 86-90% triploidy induction for pressure shock at9500 psi for exposure time of 5 minwith 72-80% survival from fertilisation to swim-up fry stage and 80% triploidy induction forheat shock at 280C for 10 min with 60-66% survival from fertilisation to fry stage. Appropriatecentigrade temperature minutes (CTM) was calculated as 300-375 min, which is variable atdifferent locations and environmental conditions. Study concluded that pressure shock ismore effective over heat shock for triploidy induction in rainbow trout. CTM, Heat shock, Karyotyping, Pressure shock,Triploidy induction