Endocrine-Nutritional Synergy Between Sex Inversion and Microencapsulated Bioactives Enhances Growth, Intestinal Development, and Oxidative Stability in Nile Tilapia Larvae.

This study evaluated the combined effects of sex inversion and microencapsulated supplementation with organic acids and essential oils on growth performance, tissue morphology, gene expression, and oxidative status in Nile tilapia (Oreochromis niloticus) larvae. A 2×2 factorial design included non-inverted (NI), sex-reversed (I), microencapsulated-supplemented (NI + M), and combined (I + M) groups. The trial lasted 28 days and used 2400 Nile tilapia larvae (GIFT strain), 6 days post-hatching, stocked at 100 larvae per tank. The experimental diets included 60 mg of 17α-methyltestosterone per kg⁻¹ of feed for sex reversal and/or 100 mg of a microencapsulated blend of organic acids and essential oils per kg⁻¹ of feed. The treatments significantly influenced zootechnical performance: weight gain was higher in sex-reversed groups at both 14 and 28 days (p < 0.001). Total length differed at D14 (I > I + M ≈ NI + M > NI; p = 0.039) and at D28 (p < 0.001). Growth modeling showed distinct patterns: NI + M had the highest asymptote (A = 198.32) with slow growth, I + M an intermediate-high asymptote (A = 123.79) with moderate growth, and NI a very low asymptote (A = 2.00) with rapid initial growth. Gene expression revealed elevated Mstn expression in NI (p = 0.0012) and higher GH in I and I + M (p = 0.0002); GHR1 and MyoD1 did not differ. Histomorphometry showed a significant interaction for villus height (interaction p = 0.004), with I + M having the highest post-hoc values (I + M vs NI, p < 0.0001). Villus width increased due to independent effects of inversion (p < 0.0001) and supplementation (p = 0.0003). Muscle height exhibited an interaction (p = 0.0098) with I + M highest, while muscle width was greater in inverted and supplemented animals (p < 0.00001). Carbonylated protein levels showed a significant interaction (p = 0.0063); NI had the highest levels and microencapsulation reduced protein carbonylation in non-inverted fish. Principal component analysis explained 71.8% of total variance and separate treatments along PC1, mainly associated with villus morphology, GH expression, and total length. Together, the results indicate that hormonal and nutritional modulation interact to enhance growth, tissue development, and redox homeostasis during early ontogeny of Nile tilapia.