Production of sterile trout (Triploids) by chromosome set manipulation using thermal shock treatment in rainbow trout (<i>Oncorhynchus mykiss</i>) from Kashmir Himalayas

Rainbow trout (<i>Oncorhynchus mykiss</i>) is a promising cultivable fish species with significant potential for expansion. As a cold-water fish belonging to the Salmonidae family, it requires an optimal temperature range of 10-15°C for optimal growth. This study explores a method for producing sterile rainbow trout with maximum survival rates by using heat shock treatment to enhance growth characteristics and improve aquaculture practices. A control group and four heat shock treatments were given at 26°C and 28°C for 10 min, applied 15 and 20 min after the mixing of eggs and milt, using a water bath. Among the treated groups, the highest fertilisation, hatching and yolk sac absorption rates were 90.3 ± 0.3%, 81.8 ± 0.8% and 83.9 ± 0.5%, respectively. The highest triploidy rate of 76.6 ± 3.3% was observed with a heat shock at 28°C, 20 min after fertilisation. In contrast, none of the fish from the control group were triploids. The control group demonstrated higher survival rates at fertilisation (93.1 ± 0.4%), hatching (84.2 ± 0.4%) and complete yolk sac absorption (86.2 ± 0.5%) compared to the heat-shocked groups. The diploid and triploid chromosome numbers in rainbow trout were determined to be 2n = 60 and 3n = 91, respectively. This study confirms that heat shock treatment can effectively induce triploidy in rainbow trout, with significant variations in triploidy rates depending on the temperature and timing of the shock. While heat shock can enhance the production of sterile fish, it is essential to balance the treatment parameters to maintain high survival rates. These findings contribute to the optimisation of triploidy induction techniques and support the advancement of aquaculture practices by improving the growth, management and survival rates of rainbow trout which could significantly benefit aquaculture efficiency and sustainability.