Full length articleEffects of dietary marjoram, Origanum majorana extract on growth performance, hematological, antioxidant, humoral and mucosal immune responses, and resistance of common carp, Cyprinus carpio against Aeromonas hydrophila
Introduction
Aquaculture importantly participates in global protein supply and suppresses the catch pressure on natural resources of aquatic organisms. Sustainable aquaculture activity directly correlates to fish farm profitability, which could be augmented by increasing growth rate and preventing diseases losses [1].
Aeromonas hydrophila, as a gram-negative bacterium, is an opportunistic fish pathogen that infects many species [[2], [3], [4]]. The outbreak of the disease is associated with stressful conditions and deteriorated fish health [5]. Antibiotics are used to cure it, but there are several reports about the rise of antibiotic-resistant isolates [6,7], the accumulation of residual antibiotics in aquaculture products [8], environmental pollution and detrimental effect on the microbial biodiversity [9]. Therefore, due to the complicated problems that the overuse of antibiotics has created, since the beginning of this century, strictly regulates have been enacted by some countries and international institutions to restrict the use of antibiotics. For example, according to the United States Food and Drug Administration and European Agency for the Evaluation of Medicinal Products, the use of several antibiotics has been prohibited in food-producing animals and animal-feed products [10,11]. Therefore, the best choice to counteract the disease is managerial issues, which suppress stress and increase health and immune of fish, enabling them to resist against A. hydrophila. One of the practical methods to achieve these goals is use of dietary supplements with growth-promoting, stress-mitigating, immunostimulating, and antioxidant properties [12,13]. Among the various feed supplements, herbal agents have recently gained a great attention due to the presence of various bioactive compounds [[14], [15], [16]]. For example, dietary supplementation with Olea europea [17], Quercus castaneifolia [18], Lavandula angustifolia [19], Camellia sinensis [20], and Ocimum sanctum [21] leaf extract have remarkably improved fish growth performance, immune and antioxidant functions, and/or resistance against A. hydrophila in different fish species.
The family Labiatae includes several plants such as Thymus vulgaris and Origanum vulgare, well-known plants with growth-promoting, antioxidant and immunostimulating effects in fish [[22], [23], [24], [25], [26], [27], [28], [29], [30], [31]]. However, little is known about the potentials of marjoram, Origanum majorana, another Labiatae plants, in aquaculture. The plant extract was found to prevent growth of different fungi and bacteria [32], including antibiotic-resistant strain of a fish pathogen, Pseudomonas aeruginosa [33]. It was found anxiolytic in rat [34] and contains high amount of phenolic compounds, sabinene and terpinen-4-ol [35,36], which have been recognized as antioxidant and antibacterial compounds [[36], [37], [38], [39]]. According to the above-mentioned health effects of marjoram, it is worthy to assess its potential in fish growth and health boosting.
Common carp, Cyprinus carpio, is one of the key aquaculture species in the world, with annual production of more than 4.1 million tons in 2017. There are reports about A. hydrophila outbreak in carp ponds [4], which rise a need for research on this topic. Accordingly, and considering the importance of this species, the goal of this research was investigating the growth-promotion, antioxidant, immunostimulant effects of oregano in common carp and their association to fish resistance against A. hydrophila infection.
Section snippets
Diet preparation and feeding trial
Marjoram leaves were purchased from a local shop and washed with deionized water. After drying against a fan blow, the leaves were powdered and mixed with 80% ethanol at a portion of 1:3 (Weight/Volume). The mixture was occasionally shaken throughout a three-day period; then filtered through a Whatman paper to obtain alcoholic extract. The extract was concentrated in rotary and kept at −20 °C until use [40]. There were four diets in this experiment, containing 0 (control), 100, 200, and
Results
According to the results (Table 2), there were significant effects of dietary marjoram extract on growth performance of the fish. Dietary supplementation with 200 mg kg−1 marjoram extract resulted in significantly higher final weight and weight gain, compared to the other treatments. FCR in the fish fed the diets supplemented with 100–400 mg kg−1 marjoram extract was significantly lower than the control treatment; the highest value was observed in the fish fed 200 mg kg−1 marjoram extract. The
Discussion
Phytotherapy is a useful means to augment fish growth performance via improvement of gut morphology, microbial community, and activity of digestive enzymes [50]. There is no study on the effects of dietary marjoram on growth performance of fish; however, other Labiatae plants including T. vulgaris and O. vulgare were found to improve fish growth rate and such improvements seem to be due to changes in gut morphology [28], microbial community [31,51] or increase in digestive enzymes’ activity [31
Conclusion
In conclusion, dietary marjoram extract seems a suitable feed additive in common carp that improve the fish growth, antioxidant and immune power, and resistance against Aeromonas septicemia. According to the results, 200 mg marjoram extract kg−1 is suitable for common carp feed formulation.
Author statement
Seyed Hossein Hoseinifar conceived and designed the experiments. Hamed Ghafarifarsani and Ghasem Rashidian performed the experiments. Hien Van Doan analyzed the data. Morteza Yousefi wrote and revised the paper. All authors read and approved the final manuscript.
Declaration of competing interest
Authors have no conflict of interest to declare for the publication of the present work.
Acknowledgment
This paper has been supported by the RUDN University Strategic Academic Leadership Program. This research work was partially supported by Chiang Mai University.
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