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.

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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.

Because of its high nutritional value, palatability and increased digestibility, fishy meal is widely used as an animal protein source in the aquafeed industry. However, the resource shortages and rising prices seriously restrict the use of fish meal (FM) in aquaculture. In this light, much efforts have been conducted to seek the sustainable supplies of protein sources to substitute FM. Due to their relatively low protein content and palatability, the presence of anti‐nutritional factors (ANFs) and unbalanced amino acid profiles, the plant protein sources have been limited in aquafeed, whereas the animal protein sources can replace FM in aquafeed due to their high protein content, total digestible dry matter and lack of ANFs. The fermentation process was recognized for its role in improving the nutritional quality of animal and plant protein sources. The protein sources can be treated with appropriate microorganisms to preserve its nutrients and finally incorporated into aquafeed, which would reduce feed costs and environmental pollution. Fermented meals showed better nutrient efficiency and could improve the nutritional value of aquafeed. This review was intended to present more updated information about the application of fermented ingredients in aquafeed industry. Based on the data collected, this review will contribute to further research into the production of fermented feed as a functional feed for sustainable aquaculture.

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The aim of this study was to assess the impact of a commercial probiotic, Sanolife PRO‐F, on water quality, growth performance, blood profiles and intestinal morphometry of monosex Nile tilapia. A field trial was conducted for 10 weeks in which tilapia fingerlings (20 ± 1.26 g) were randomly distributed into three replicate ponds which were subdivided into three treatment groups, receiving Sanolife PRO‐F at 0 (B0), 0.1 (B1) and 0.2 (B2) g/kg diet, respectively. The results showed a significant improvement in growth performance, feed conversion ratio and blood profiles in tilapia fed on treated diets. The whole intestinal lengths, anterior and terminal intestinal villi heights and anterior goblet cells count were greater in tilapia fed on treated diets. There were no noticeable differences in growth and intestinal morphology between tilapia fed on B1 and B2 diets. The ammonia concentration in water was lower with B1 diet while electric conductivity, salinity and total dissolved solids were higher with the B2 diet. The pH level of pond water was enhanced by both diets, B1 and B2. In conclusion, application of Sanolife PRO‐F at 0.1–0.2 g/kg diet might have beneficial effects on growth, immunity, stress responses and gut health and function as well as the water quality of farmed Nile tilapia.

Vitamins are organic compounds that can be synthesized from other essential nutrients; however, they are required in trace amounts from an exogenous source for normal growth, reproduction and health. Vitamin C (ascorbic acid, AA) is an essential micronutrient for normal growth and physiological function of most aquatic animals. In terrestrial animal nutrition, vitamin C has recently spurred scientific interest because of the increasing knowledge on vitamin C involvement in gene expression, cell cycle and reproduction in mammals; in addition, recent advances in molecular biology techniques allow the more effective estimation of the effect of vitamin C on metabolism and physiology. In contrast, this information is scarce in aquatic animal nutrition, as studies have essentially focused on the estimation of minimum vitamin C requirement for maximum growth and immune response as well as for the formulation of least‐cost diet. This scarcity of information is also due to the lack of well‐established indicators of vitamin C status in aquatic organisms. The present review summarizes and discusses information about vitamin C sources, bioavailability, deficiency and requirement in aquatic animals to plan further studies. In the future, vitamin C nutrition studies in aquaculture should also include immune responses, histopathology of the gills, liver, gonad development, gamete quality and quantity, fecundity, larvae survival and gene expression. Dietary vitamin C requirements should be estimated at every life‐history stage of cultured species. All this information will allow a better understanding of the essentiality of vitamin C in aquatic animal growth, development, reproduction and health.