The use of medicinal plants as immunostimulants in aquaculture: A review

Medicinal plants have been known as immunostimulants for thousands of years. The application of medicinal plants as natural and innocuous compounds has potential in aquaculture as an alternative to antibiotics and immunoprophylactics. The growing interest in these plants has increased world-wide because they are easy to prepare, cheap, and have few side effects on animals and the environment. A wide range of medicinal plants such as herbs, spices, seaweeds, herbal medicines, herbal extracted compounds, traditional Chinese medicines, and commercial plant-derived products has been studied in various aquatic animals. The whole plant or its parts viz. roots, leaves, seeds, flowers or extract compounds can be used. The extraction process is simple, with ethanol and methanol being commonly used. Various chemicals used to extract compounds may lead to different degrees of effects on aquatic animals. Application methods can be either single or in combination, or even in a mixture with other immunostimulants, via water routine or feed additives and enrichment, where single administrations are as practical as combinations. The dosages and duration of time varies and the optimal levels have not been considered. Medicinal plants show their main properties as growth promoters, immune enhancers, where they act as antibacterial and antiviral agents to the host immune system. Unfortunately, the mechanisms are not fully understood. Therefore, most authors did not recommend that their results be used directly, while suggestions are proposed for further investigations.