Effect of dietary vitamin C dosage on rearing performance and hematological indices in swamp eel ( <i>Monopterus albus</i> Zuiew, 1793) juveniles

The swamp eel ( Monopterus albus ) is a freshwater species widely cultured in Southeast Asia due to its high nutritional and economic value. Vitamin C is required for antioxidant defense, immune function, and collagen synthesis as a cofactor for fish health and growth. This study examined the effects of five dietary vitamin C (L-ascorbic acid) supplement levels (0, 80, 140, 200, and 260 mg/kg) in pellet feed on the growth performance and hematological indices of M. albus juveniles. A 60-day feeding trial was carried out using a completely randomized design with three replicates on the juveniles (initial average sizes of 5.61 g and 18.69 cm) in rectangular Styrofoam basins with a volume of 16.4 liters. From day 15 onward, most of the weight growth parameters progressively increased with dietary vitamin C levels (80–260 mg/kg), with significant improvement at ≥200 mg/kg (P ≤ 0.05); however, there was no difference between 200 and 260 mg/kg (P ≥ 0.05). Length growth parameters did not differ significantly at vitamin C levels of 80–200 mg/kg (P ≥ 0.05), but significant differences in length means, daily length gain, and specific length growth rate were observed between 260 and 0 mg/kg (P ≤ 0.05). There was no significant difference in most hematological indices at the treatments (P ≥ 0.05), except for mean corpuscular hemoglobin, which declined significantly at ≥ 200 mg/kg (P ≤ 0.05). Mid-sized cells and granulocytes showed no consistent response to the tested vitamin C levels. The findings indicate that dietary vitamin C had minimal effects on hematological indices, with 200 mg/kg recommended as the optimal supplementation level for rearing M. albus juveniles under the study conditions.