Phytotherapeutics for parasite control in global fish aquaculture: a review of anti-monogenean agents and their mechanisms

With the intensification of fish cultivation, also increased threat of parasitic diseases to fish health, growth, production, and productivity. This has had huge negative impacts and necessitate alternative therapeutics for the control and treatment of diseases. Medicinal plants have been integral to human life, utilized as a natural source of bioactive compounds for use in veterinary and human medicine. These plants produce diverse chemical compounds, such as alkaloids, saponins, phenolic compounds, tannins, terpenoids, steroids, flavonoids, and essential oils, which have been used in fish aquaculture. Thus, the present study aimed to synthesize papers published within the last eight years on the efficacy of different extracts, essential oils, and bioactive compounds derived from medicinal plants, as well as their potential modes of action on fish parasites, with an emphasis on fish parasitic monopisthocotylans and polyopisthocotylans (formerly monogeneans). Data on phytotherapeutic products, phytochemicals, targeted parasites, and in vitro and in vivo experiment outcomes were extracted from the literature and summarized. Additionally, the mechanisms by which these phytotherapics act on parasites were shown and discussed. The bioactivity of essential oils and crude herbal extracts in controlling and eliminating parasites is directly linked to the action of their major components, which demonstrate parasiticidal and anti-monopisthocotylans and polyopisthocotylans activity, even when isolated. This provides a wide range of options. Phytotherapeutic agents are an alternative to chemotherapeutic agents because they pose no risk of acute or chronic toxicity to host fish, nor do they contaminate handlers. They also do not cause parasitic resistance and are environmentally friendly. Therefore, they are recommended for use in management strategies to control and treat parasite infections in fish aquaculture due to their anthelmintic and parasiticide properties. Lastly, although the economic and aquaculture viability of phytotherapeutic agents is unknown, the environmental benefits are evident compared to the widespread use of chemotherapeutics.