Optimization of Heat Shock Protocol for Triploidy Induction in All-Female Rainbow Trout (Oncorhynchus mykiss)

This study aimed to optimize heat shock conditions for triploidy induction in all-female rainbow trout (Oncorhynchus mykiss) under controlled hatchery conditions. The experiment included a control group and two experimental groups. The first group consisted of eggs obtained from neo-males fertilized with natural females (treatments 1–27), and the second included eggs from natural male and female parents (treatments 28–54). Eggs were exposed to heat shock at 23, 25, and 27°C for 15, 17, or 19 minutes at 15, 17 and 19 minutes post-fertilization. Sperm used for fertilization was selected based on high motility, and eggs were handled under standardized conditions to minimize variability. Larvae were reared on a commercial diet until four months, and survival rates and triploidy success were evaluated. Survival rates at different developmental stages did not differ significantly among control and treated groups (P>0.05). In triploid individuals, erythrocyte nuclear volume and cell size were 2.38 and 1.57 times larger than diploids. The highest triploidy percentage was observed under 27°C for 19 minutes, applied 17 minutes post-fertilization; however, variation indicates sensitivity to precise timing and conditions. These findings suggest a practical, cost-effective approach for producing all-female triploid rainbow trout under controlled hatchery conditions.