Reproductive Traits in Different Genetically Improved Nile Tilapia (Oreochromis niloticus) Strains Raised in Brackish Water

Inland aquaculture using underground brackish water is a promising method to alleviate pressure on freshwater resources. Nile tilapia stains utilized for commercial production can also tolerate low-salinity brackish water. Therefore, the goal of this study was to compare the reproductive performance of females and males of five genetically different Nile tilapia strains under brackish water cultivation. The GIFT, Big Nin, Mag Nin, Thai red, and Taiwanese red strains, with initial mean weights of 165.5 ± 18.3, 157.8 ± 26.1, 157.1 ± 27.6, 163.3 ± 26.3, and 175.9 ± 27.3 g (±standard deviation), respectively, were used. The fish were individually tagged and each strain was maintained in 8 m² rectangular concert tanks for 120 days (two fish/m²). The fish were fed at 1.5% of their body weight twice a day with a commercial diet (42% crude protein) at 29.0 ± 0.5°C. The highest female body weight was obtained in the red color strains (Thai and Taiwanese strains) compared to Big Nin strain (p < 0.05) and it was not significantly different in other black tilapia strains. The results of the reproductive indices including spawning frequency and cycles, fertilization and hatching rates, and hepatosomatic index indicated no significant differences among the strains (p > 0.05). However, Mag Nin strain exhibited higher working and relative fecundity values than GIFT strain. A longer reproduction cycle was recorded in GIFT strain than Taiwanese red strain (p < 0.05). In terms of egg quality, no significant differences were obtained among the tilapia strains. A higher sperm motility was recorded in GIFT strain than Mag Nin strain, while other groups showed no significant differences. Overall, GIFT strain demonstrated superior values of sperm motility and reproduction cycles, while Mg Nin strain showed high working and relative fecundity values. The results of the reproductive performance of each genetically improved Nile tilapia strain will be discussed by fish farmers upon their specific environmental conditions and production goals.