The use of antibiotics in the aquafeeds to mitigate infectious diseases or to boost growth performance is commonly practiced. Recently, the prophylactic use of antibiotics and chemotherapies have been criticized which eventually led to their ban in aquaculture by law on many countries. In view of the current restrictions on antibiotic use, there is a critical need to evaluate other possible alternatives. One potential substitute for antibiotics in aquafeeds is the use of functional feed additives. The present review is a comprehensive and an updated compilation of the available works on different feed additives, their examples, modes of action and useful applications for improving aquafeeds. It highlights several functional feed additives including probiotics, prebiotics, synbiotics, immunostimulants, organic acids, nucleotides and medicinal herbs. Apart from boosting aquafeeds and safeguarding general health of aquatic animals, some of these substances have been found to possess beneficial immunostimulant and anti‐stress relieving properties. Furthermore, the use of these natural substances increases the consumer confidence of farmed fish. Due care has been taken to cover the on‐going trends and recent advances with a perspective vision and their holistic usages and beneficial applications in aquatic animals’ systems. The current study also shed light regarding the management and production aspects of aquatic animals which will enlighten farmers and producers for better economic growth.

Intensive culture systems are usually employed to increase the production, but we suspect that, in such systems, fish suffer infection and stress, which weakens their health. However, such systems may fail due to lack of resources or difficulty in controlling the rearing conditions' optimization. When intensive culture systems fail, aquatic animals gradually stop feeding. Accordingly, their physiological status deteriorates, and their immunity is suppressed. Through some strategies, it is possible to protect fish from disease by providing balanced food that maintain intestinal health and improve digestion, thereby increasing immunity. Protecting the health of the intestinal barriers is the primary guarantee of fish health. The local immunity of the intestine is associated with the innate and adaptive immunity of the fish's entire body. Thus, it is necessary to understand the interaction between the gut microbiota and the general immune system, as well as the most important reasons that can increase or suppress intestinal immunity. Many studies have confirmed that balanced diets containing basic nutritional requirements are the primary factor for maintaining intestinal health in aquatic animals. Another strategy for improving the intestine's local immunity is to use some non-nutritional food additives that increase the activity of beneficial bacteria and the secretion of digestive enzymes and decrease the harmful bacteria. This review article aimed to clarify the relationship between a balanced aquafeed and the intestinal health of aquatic animals by discussing the findings of related studies. Awareness of this correlation between diet and intestinal health is expected to aid the aquaculture industry to develop proper nutritional strategies that ensure the protection of fish health.

Aquaculture, which constitutes one of the largest food production sectors in the world, is preferably practiced with natural organic products rather than with synthetic chemicals or antibiotics. In addition to the daunting challenge of providing food and livelihood to the exponentially increasing world population, the aquaculture industry is key to ensuring that development is based on environmentally sustainable practices, specifically in the production of aquafeeds. Terrestrial microorganisms that act as natural defence systems of cultured species have been identified as the main producer for the beneficial bacterial candidates. Probiotics have recently gained popularity as beneficial microbes candidates in cultured organisms to maintain the health condition and well-being of different aquatic animals. This review aimed to understand the necessity of using probiotics as a sustainable alternative to regulate the growth performance, feed utilisation and general health condition for sustainable aquaculture. Also, explanatory discussion about the host microbiota and its ability to produce different probiotic strains and the probiotic functionality to ameliorate the host immunity to provide the interactive effects on the host-derived probiotics. By presenting the results obtained from the previous studies about the ability of probiotics to sustain the aquatic animal's performances, this study condensed the current knowledge and information for future research and development of the probiotic application in aquaculture.