A Review on the Application of Phytogenics as Feed Additives for Aquatic Animals

Feed preparation is the most expensive part of the aquaculture industry. In recent years, studies have been conducted on the utilization of plants’ wastes and by-products (such as peel, pulp, and kernels) as phytogenetic materials and sources of protein and nutrients for preparing feed in the aquaculture industry, which have yielded promising results. These wastes are recycled by processing as feed additives and returned to the feed chain, and because they are waste products of plants and fruits, prepared phytogenic feed additives cannot be regarded as feed sources for humans. In the future, there will be large quantities of fruit and vegetable waste, which have the potential to be recycled and returned to the feed chain by being processed as additive feed for aquatic animals. Phytogenics encompass a wide range of substances that can be classified based on plant origin, the processing method, and composition but generally found in the form of herbs and spices, or as plant extracts, essential oils, and oleoresins. The phytogenic properties of plants are related to the various secondary metabolites produced by them. These metabolites are used as growth and appetite stimulants. Furthermore, these metabolites induce the secretion of bile and other digestive enzymes. They are not a threat to the environment, and their benefits as substitutes for antibiotics have been promising. The antioxidant, anti-cancer, analgesic, antimicrobial and antiparasitic effects of these products have been proven so far but the main function reported for these compounds in the host is to improve gastrointestinal microbiota and immune function (modulating cytokine production by epithelial cells). However, the mechanisms of action of these products are not yet completely understood, and further studies are needed to divulge the potential side effects of phytogenic substances on the host, the environment, and on gastrointestinal microbiota. Understanding these mechanisms will ensure us about the safety of these herbal additives for fish, consumers, and the environment. Despite some applications of plant materials in aquaculture, their widespread use for feed preparation is still limited due to the lack of sufficient knowledge on the mechanisms of action of phytogenic materials. So, a better understanding of the effects of these compounds, which are derived from plant and fruit wastes, on the host’s physiology will provide us with the opportunity to use these substances more widely in the aquaculture industry. In the present review, we discuss the studies conducted on the use of phytogenic materials as feed additives for aquatic animals, as well as their effects, advantages, and disadvantages.