Abstract
Medicinal plants are increasingly used in aquaculture owing to their beneficial impacts on the health status of farmed fish. The current study was conducted to investigate the effect of nutmeg (Myristica fragrans) extract on growth, immunity, antioxidant parameters, and resistance of common carp (Cyprinus carpio) against Aeromonas hydrophila. In addition, in vitro antibacterial activity of the skin mucus of fish fed on nutmeg extract was evaluated against three major fish pathogenic bacteria through the standard disk diffusion method. Fish (17.27 ± 0.11 g) were divided into four groups and fed on experimental diets containing different levels of nutmeg extract, including zero (control), 0.5% (M1), 1% (M2), and 2% (M3) per kg diet. Results showed that nutmeg significantly enhanced growth parameters after a four-week feeding trial. Feed conversion ratio was remarkably reduced with the lowest value reported for the M3 group, whereas weight gain was notably increased in M2 and M3. No significant effect was found on the hematological profile, including mean corpuscular hemoglobin concentration, mean corpuscular hemoglobin, mean corpuscular volume, and hematocrit, while the highest levels of red blood cells and white blood cells were found in the M3 group. Stress biomarkers, including glucose and cortisol, were the lowest in the M3 group. Serum and skin mucus immunological and antioxidant parameters were significantly higher in M3, followed by M2, where the highest resistance was also observed. In addition, skin mucus samples effectively inhibited Streptococcus iniae, Yersinia ruckeri, and Aeromonas hydrophila. Overall, the present results suggest that dietary nutmeg (20 g/kg diet) could be used as a growth promotor and immunostimulant in common carp.
Highlights
Aquaculture supplies more than 60% of the world’s food fish, and its further expansion seems inevitable
Including final weight, weight gain, and specific growth rate compared to other treatments
The lowest feed conversion ratio was recorded in the M3 group, while other treatments showed no significant difference when compared to the control
Summary
Aquaculture supplies more than 60% of the world’s food fish, and its further expansion seems inevitable. Feed additives have been evaluated for the improvement of feed utilization, growth performance, immune responses, and resistance against various pathogens [1–4]. Natural feed additives, such as medicinal plant extracts, have been demonstrated to be efficient in reducing the need for chemical treatments or antibiotics, decreasing metabolic waste production, and improving fillet quality [5–13]. Nutmeg (Myristica fragrans) is a dark-leaved evergreen tree cultivated for two spices derived from its seed (nutmeg) and seed covering (mace). It is a commercial source of essential oils and nutmeg butter [14].
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