The aquaculture industry is expected to grow in the coming decades to feed a growing population with delicious and nutritious fish and seafood. However, this rapid expansion faces a significant obstacle: diseases.
Traditional methods often heavily rely on antibiotics, raising concerns about environmental pollution and the emergence of antibiotic-resistant bacteria. Fortunately, there is a powerful and ecological solution: medicinal plants.
Researchers from the University of South Bohemia in Ceske Budejovice published a scientific review providing an overview of recent evidence on the benefits of using medicinal plants to promote growth and strengthen the immune system in aquatic animals used in aquaculture.
Medicinal plants among the best alternatives
Medicinal plants contain substances with biological modulation functions, such as promoting growth, anti-stress effects, appetite stimulation, disease resistance, and antimicrobial activities.
The study discusses the adoption of plants in the form of roots, leaves, flowers, and processed forms, including active compounds, extracts, raw forms, and combinations.
Medicinal plants and aquaculture
According to the study, many of the antimicrobial substances in medicinal plants are potential candidates to combat a wide range of pathogenic microorganisms. Studies have reported that plant compounds have been used to combat pathogenic bacteria, fungi, and viruses.
Medicinal plants are also used as chemotherapeutics and food additives. These plants can be administered in various ways, either as a whole plant or in parts (leaf, root, seed, fruit), and can be applied fresh or as herbal extracts prepared with different solvents (water, methanol, chloroform, ethyl acetate).
Biological activity of plants in fish
“The main target organs of fish influenced by medicinal plants are the thymus, spleen, kidneys, and intestines, promoting the development of the immune system. Medicinal plants can directly improve antibody production and specific immune response,” the study reports.
The researchers highlight that the biological activity of medicinal plants is attributed to their secondary metabolites, such as essential oils, saponins, phenols, tannins, alkaloids, polypeptides, and polysaccharides.
The study reports that medicinal plants can stimulate appetite and promote weight gain by increasing digestive enzymatic activity.
Some experiences cited in the study include the use of sissoo spinach (Alternathera sessilis), false daisy (Eclipta alba), and devil’s backbone (Cissus quadrangularis) to improve the protease, amylase, and lipase activities of freshwater prawns. Additionally, the addition of wormwood extract (Artemisia annua) had a growth-promoting effect on rainbow trout, largemouth bass, and carp.
Anti-stressors and immunostimulants
Several studies recommend the use of natural compounds to defend fish against stress induced by external signals (e.g., poor water quality). The anti-stress effects of medicinal plants have been mentioned in various scientific studies.
On the other hand, several studies have focused on using plant extracts as immunostimulants in fish. “According to scientific studies in fish species, intraperitoneal injection or oral administration of plant extracts improves phagocytic and lysosomal function, respiratory burst, complement activity, and serum protein levels,” the study cites.
Various in vitro and in vivo studies have demonstrated the potential of medicinal plants against a wide range of marine pathogens.
According to the study, the antiviral activity of some plant species has been reported in different diseases, such as white spot syndrome virus (WSSV), grouper iridovirus (GIV), grass carp reovirus (GCRV), spring viremia of carp virus (SVCV), and cyprinid herpesvirus 2 or 3 (CyHV).
Medicinal plants can be considered an alternative to treat ectoparasites. The study presents several examples where extracts of peppermint (Mentha piperita) were used to treat tilapias affected by parasites.
Moreover, studies have shown that white spot disease caused by Ichthyophthirius multifiliis can be controlled with ginger (Zingiber officinale), sweet wormwood (Artemisia annua), tea tree (Melaleuca alternifolia), English lavender (Lavandula angustifolia), among other plants.
“Medicinal plants exhibit promising potential for the current needs of intensive and large-scale production in the aquaculture industry and are a substitute for chemotherapy in treating fish disease outbreaks,” conclude the study’s authors. In this regard, medicinal plants become an important alternative to the use of antibiotics in aquaculture.
However, scientists warn that the toxicological effects of medicinal plants and their modes of action need to be studied, as well as their combination with other inputs such as probiotics.
The study was funded by the Ministry of Agriculture of the Czech Republic and the Ministry of Education, Youth, and Sports of the Czech Republic.
University of South Bohemia in Ceske Budejovice
Ceske Budejovice, Czech Republic
Reference (open acces)
Dadras F, Velisek J, Zuskova E. An update about beneficial effects of medicinal plants in aquaculture: A review. Vet Med-Czech. 2023;68(12):449-463. doi: 10.17221/96/2023-VETMED.