The quality and price of feed ingredients and additives used to feed aquatic products directly impact the feed, which can be considered the most significant expense in production. In other words, a large portion of the cost of the fish presented to the market stems from the feed given to them. Therefore, it is crucial for farmers to carefully evaluate the quality of feed ingredients and additives and make appropriate choices within their budgets. While there are raw materials and additives of every quality available in the market, those of higher quality can enhance the digestibility of feeds and also be more nutritious. However, these advantages will also increase the cost. Even the cost per unit alone requires farmers to make considerable efforts to find suitable resources. Continuous research is being conducted to find the most beneficial, highly digestible, and least residue-inducing feed in order to reduce costs.

Using feeds that appear cheap but are low in quality in terms of functionality may seem important for cost reduction and valuable for budget management. However, it carries significant risks for the health of the fish under the aquaculture operation and the resulting growth after feeding. Ultimately, if the benefits obtained from the feed are low, the cost of aquaculture can become higher than initially calculated. The most important thing to remember here is that the quality of the feed and its cost are directly proportional, meaning they increase or decrease together.

Feeds are prepared using appropriate and necessary raw materials, along with additives that can enhance the quality and value of the feed. Among these additives, functional feed additives have gained attention due to their ability to increase the feed's quality and value compared to other components used in feeds. They have become noticeable for being more environmentally friendly, sustainable, and cost-effective options. Functional feed additives, which can be classified as a promising development in aquatic animal feeds, positively improve the growth performance of the crops fed with supplemented feeds and play a significant role in maintaining the health and stability of these crops under cultivation. The proper use of feed additives is an important part of adopting a sustainable approach in aquaculture. 

When selecting and including these additives in feeds, attention should be paid to their interactions and synergy with each other.

Diseases are undesirable occurrences that are expected to be minimized in aquaculture operations. The cost of treating a disease is generally higher than preventing its occurrence. Therefore, improving aquaculture conditions and preventing the conditions that lead to diseases in facilities are desired. The easiest and fastest way to provide resistance against diseases and strengthen the immune system is to incorporate substances that enhance resistance, essential nutrients, and bioactive compounds into the fish's immune system. After this incorporation, fish can better combat pathogens that cause diseases and environmental stress. This leads to increased survival rates and higher productivity in aquaculture.

In the context of aquaculture focusing on human consumption, functional feed additives can also be used to improve and enhance the nutritional values of fish. A prime example of this is increasing the amounts of essential nutrients such as omega-3 fatty acids and vitamins per unit mass in fish. By feeding fish with a high-quality and nutritious diet in terms of content, healthy and sustainable seafood production can be achieved for the target audience of the cultivated species.

Another application of functional feed additives is to enhance the absorption of nutrients in the intestines of fish, thereby strengthening the digestion of the feed. In the process of digestion, it is important to maintain the health of the intestine, which is the most important organ in the fish's body, and increase its resistance to stress. Any disruption in the intestine, where many bacteria that assist in digestion are present, can lead to uncontrolled growth of certain bacterial groups, resulting in illness. Functional additives help protect the intestinal health of fish, increase their resistance to stress factors, and strengthen their immune systems.

Among functional feed additives, the most notable ones include prebiotics, probiotics, seaweeds, fungi, microalgae, enzymes, organic acids, mycotoxin binders, yeasts, essential oils; steroids, terpenoids, phenolics, pigments, flavonoids, and alkaloids, which are collectively referred to as phytogenic or phytochemical compounds. These compounds have managed to find their place in the feed industry. Prebiotics promote the growth of beneficial bacteria in the fish intestine, maintain gut health, and enhance disease resistance and reduce the presence of potentially harmful bacteria in the feed and increase the population of beneficial bacteria in the fish intestines. The main objective here is to protect the intestinal health of fish in aquaculture and prevent them from falling disease by strengthening their immune system.

Functional feed additives that can be used to cope with inflammation resulting from protection and microbial activities, there are micro and macroalgae, fungi, and yeast. These substances are added to feeds due to their antioxidant, anti-inflammatory, and antimicrobial benefits. They are particularly noteworthy for their potential to reduce the use of antibiotics and other chemotherapeutics, which have negative effects on the perception of aquaculture in terms of resistance formation, environmental pollution, and food safety. They are rapidly progressing as efficient alternatives to therapeutic drugs. Furthermore, compounds derived from seaweeds, such as resins, alginates, and carrageenans, are used to position the feed underwater, promoting more appetitive consumption by fish.

Understanding the biochemical and physiological functions of functional feed additives in animals, their integration and widespread use in feeds, are important for making aquaculture more sustainable and environmentally compatible.