Effect of dietary garlic ( Allium sativum ) powder dosage on growth and hematological indices of swamp eel ( Monopterus albus Zuiew, 1793) fry

The swamp eel ( Monopterus albus ) is a commercially significant freshwater species that is widely cultivated in Asia. Garlic ( Allium sativum ) is known to contain bioactive compounds that possess antimicrobial, antioxidant, and immunostimulatory properties, and it has increasingly been used as a natural feed additive in aquaculture. This study examined the effects of dietary garlic powder levels (0, 5, 10, 15, and 20 g kg⁻¹) on the growth performance and hematological indices of M. albus fry over two consecutive 45-day rearing phases. The experiments were conducted using a completely randomized design with three replicates in 16.4-liter plastic trays containing 4 cm in Experiment 1 and 7 cm in Experiment 2. In Experiment 1, fry were used at the onset of exogenous feeding (0.026 ± 0.003 g). The 10 g kg⁻¹ dosage significantly improved weight gain, daily weight gain, specific growth rate in weight, and feed conversion ratio (FCR) compared to higher dosages (15–20 g kg⁻¹) (P ≤ 0.05). Survival was significantly higher at 10–15 g kg⁻¹ than for those at other levels (P ≤ 0.05). Erythrocyte, leukocyte, lymphocyte, and monocyte counts peaked at 5 g kg⁻¹ and significantly declined at 15–20 g kg⁻¹ (P ≤ 0.05). Experiment 2 used larger fry that had been pre-reared for 45 days (0.84 ± 0.24 g). No significant differences in growth or length parameters (P ≥ 0.05) and survival reached 100% across all groups, while fry fed a 10 g kg⁻¹ dosage exhibited a significantly lower FCR (P ≤ 0.05). Erythrocyte counts remained stable at 0–10 g kg⁻¹ and gradually decreased at higher dosages. Leukocyte, lymphocyte, and monocyte counts increased significantly at 5 g kg⁻¹ compared with the control (P ≤ 0.05) and remained stable across the 5–20 g kg⁻¹ range, while neutrophil counts were significantly elevated at 5–10 g kg⁻¹ (P ≤ 0.05). Overall, dietary garlic powder at 5–10 g kg⁻¹ appears optimal for balancing growth, feed efficiency, survival, and hematological stability, whereas higher levels may inhibit growth performance and physiological status in M. albus fry.