Dietary organic acid blend modulates hemato-immunological parameters, digestive and reproductive performances in red tilapia (Oreochromis niloticus × O. mossambicus) broodstock

This study evaluated the effects of dietary organic acid (OA) blend on hemato-immunological responses, reproduction capacity, gene expression, and histological features of red tilapia (Oreochromis niloticus × O. mossambicus) broodstock. Four diets were formulated, containing 0 (control), 2, 3, and 4 g OAs kg^-1. The diets were fed to triplicate groups (n = 3) of red tilapia broodstock (75 ± 5.56 g( (mean ± standard deviation (SD)) stocked in 10-m³ concrete tanks at a male to female ratio of 1:3, to satiation, twice a day, for 8 weeks. At the end of the feeding trial, fish in each tank were collected, counted, and weighed. Blood samples were collected from five fish from each tank and used for the determination of hematological and biochemical parameters. The fish were then dissected to study the reproductive performance and reproduction-related genes. The red blood cells (RBCs), hemoglobin (Hb), packed cell volume (PCV%), mean corpuscular volume (MCV), and lysozyme activity were significantly increased (P < 0.05) with increasing dietary OAs to 4 g kg^-1. Mean corpuscular hemoglobin (MCH), white blood cells (WBCs), total protein, albumin, and globulin), and digestive enzyme activity values leveled off or slightly decreased (P > 0.05) at OA levels above 3 g kg^-1. Optimum liver enzyme activity was obtained at 2 g kg^-1 OA. The reproductive hormones: testosterone (T), follicle-stimulating hormone (FSH), luteinizing hormone (LH), estradiol (E2), and progesterone (Prog), organo-somatic index (GSI), reproductive performance, and the expression of reproductive genes (vasa, nanos1a, nanos2, dnd1, pum1, amh, and VTG) exhibited dose-dependent responses (P < 0.05), suggesting that 4 g OA kg^-1 boosted the optimum reproductive performance. In conclusion, about 2-3 g OA kg^-1 diet can improve the hemato-biochemical parameters, immune response, antioxidant status, and digestive enzyme activity in red tilapia broodstock, whereas 4 g kg^-1 could accelerate their reproductive performance through upregulation of reproductive genes.