Essential oil of Curcuma aromatica as a dietary supplement: Evaluation of its effect on growth, haematology, immune response and histopathology in Channa punctata challenged with two pathogenic aeromonads

A seven-week feeding trial was conducted to examine the effect of dietary inclusion of Curcuma aromatica essential oil (CAEO) as supplementary feed additive on growth performance, haematological parameters, immunological responses and histological changes in Channa punctata. A total of 675 fish (initial body weight of 4.44 ± 0.23 g) were randomly distributed in 27 tanks with 25 fish per tank (3 treatments with 3 replications) and fed with diets containing essential oil extracted from rhizome of Curcuma aromatica (CAEO) at concentrations 0.00, 0.25 and 2.00 mL per kg feed. Each of the experimental feeding groups was further divided into 3 sub-groups C: not challenged with bacteria, RD-01: challenged with Aeromonas veronii, RD-05: challenged with Aeromonas hydrophila. The first experimental phase consisted of feeding fish for the first four weeks, and in the second phase, the fish were challenged with LD₅₀ of A. veronii (2.6 × 10⁴ CFU/fish) and A. hydrophila (1.6 × 10⁴ CFU/fish) with continued feeding for remaining three weeks. The final weight gain and specific growth rate were found to be significantly increased (P < 0.05) in the group fed with supplemented diet containing 2.00 mL/kg concentration. Cumulative mortality was recorded for 3 weeks post-challenge which showed higher percentage of survival rate (>95 %) in groups fed with 2.00 mL CAEO/kg diet, where RD-01 and RD-05 sub-groups had a survival rate of 98 % and 96 %, respectively. The haematological values were significantly higher in both challenged and unchallenged groups fed with 2.00 mL CAEO/kg diet. The total protein content, total immunoglobulin concentration and lysozyme activity significantly increased in groups fed with 2.00 mL CAEO/kg diet, in which RD-05 showed the highest values. Comparable histological differences were prominent in liver and kidney tissues of fish fed with 0.00 and 2.00 mL/kg diets. The study illustrated that the dietary supplementation with 2.00 mL CAEO/kg feed is highly effective to enhance growth and health in Channa punctata and increase bacterial resistance to Aeromonas species.