Editorial for the Special Issue on the Pivotal Roles of Feed Additives for Fish

Nutrition plays a vital role in the aquaculture industry, particularly in fish farming, as it significantly influences operational costs, zootechnical performance, animal health, product quality, and the sustainability of production systems. The nutrition of aquaculture species has become a major focus for researchers worldwide, with a substantial body of research published in recent years. Providing balanced diets for farmed aquatic animals can improve feed conversion efficiency, reduce operational costs, and minimise disease-related losses. Furthermore, appropriate nutritional strategies can decrease the excretion of nitrogenous and phosphorus wastes into the environment, thereby mitigating ecological impacts and promoting industry sustainability [Contributions 1–5].

This Special Issue (SI), entitled “Pivotal Roles of Feed Additives for Fish”, was launched to advance understanding of the role of feed additives in fish nutrition. The collection has received over 15,000 page views, underscoring the growing global interest in fish nutrition research. Five articles were ultimately included in this issue. The research article entitled “Pivotal Roles of Fish Nutrition and Feeding: Recent Advances and Future Outlook for Brazilian Fish Farming” [Contribution 1] has attracted over 7800 views and received 17 citations within just 12 months of publication, earning its inclusion in the Editor’s Choice Articles of Fishes.

Fish farming plays a central role in global aquaculture, generating employment, income, and broader economic benefits. Scientific and technological advances in aquafeed development have contributed significantly to improvements in production efficiency. The use of feed additives, supplements, and alternative ingredients has enhanced fish performance, health, and welfare. In countries such as Brazil, nutritional strategies are fundamental to the advancement of fish farming practices, with a marked increase in research initiatives aimed at developing more sustainable and efficient feeds. Such progress is crucial for the future of sustainable aquaculture. However, these innovations must be effectively adopted by the aquafeed industry in order to foster continued sectoral growth and long-term sustainability [Contribution 1].

Recent breakthroughs have demonstrated that fish feed additives, such as probiotics, can enhance the efficiency of integrated animal–plant aquaculture systems, particularly in aquaponics. Probiotic preparations are increasingly recognised for their capacity to regulate pathogen proliferation in aquaculture systems, thereby improving water quality, increasing the survival rates of aquatic organisms, and stabilising hydrochemical conditions in recirculating aquaculture systems. A novel class of probiotics derived from eurytopic soil bacteria of the genus Bacillus is now being introduced into aquaponic systems. These probiotics possess a distinctive capacity to adapt to and thrive in diverse environments under varying conditions, offering the potential to optimise productivity across all aquaponic components, including animals, plants, and microbial communities [Contribution 2].

The use of fishmeal in the aquafeed industry remains a major source of controversy in aquaculture. Although fishmeal constitutes a high-quality protein source for farmed fish, the overexploitation of small pelagic fish stocks raises significant ecological, social, and economic concerns at a global scale. The replacement of fishmeal with alternative protein sources represents a considerable challenge, particularly in the nutrition of carnivorous species. Several studies have suggested that fermented soybean meal may serve as a nutritionally viable alternative to fishmeal in aquafeeds. However, evidence indicates that its inclusion as a replacement can affect nutrient utilisation efficiency in aquatic species. Notably, dietary supplementation with fermented Lentinus edodes has been shown to alleviate hepatic and intestinal damage, enhance antioxidant capacity, and improve immune responses in Japanese eel (Anguilla japonica) when fishmeal was substituted with fermented soybean meal. In addition, this feed additive has been reported to reduce splenic inflammation, thereby contributing to improved overall health [Contribution 3]. Although the replacement of fishmeal with alternative protein sources, such as fermented soybean meal, continues to present limitations associated with digestibility and nutrient utilisation efficiency, complementary nutritional strategies have demonstrated promising potential.

Nutritional engineering in aquaculture can be applied to aquafeeds to formulate diets that enhance the performance, health, and nutritional status of aquatic animals, while also producing end-products with added nutritional value for consumers. Trace elements, for instance, are essential for a wide range of physiological and biochemical functions in the human body. Strontium, a trace element structurally and chemically similar to calcium, has been associated with roles in bone regeneration and the management of osteoporosis, exhibiting antibacterial and anti-inflammatory properties. Consequently, aquaculture products enriched with strontium may attract increasing consumer interest. This potential was demonstrated in a study involving hybrid sturgeon (Acipenser baerii ♀ × Acipenser schrenckii ♂), in which juveniles were fed diets supplemented with graded levels of strontium chloride for eight weeks. Although dietary strontium did not significantly influence growth performance or survival rates, tissue strontium concentrations increased in accordance with dietary inclusion levels. These findings suggest that controlled strontium enrichment in hybrid sturgeon may enhance the nutritional value of their fillets [Contribution 4]. Overall, this evidence highlights the potential of feed-based nutritional engineering as a practical strategy to improve the functional attributes of aquaculture products, while aligning with human health considerations and evolving consumer preferences.

Likewise, current research has increasingly focused on sustainable ingredients capable of enhancing the health, performance, and resilience of farmed fish, while preserving the nutritional quality of the final product. A notable example is the incorporation of seaweeds as functional ingredients or dietary supplements in aquaculture. Seaweeds contain a range of bioactive antioxidant compounds, including sulphated polysaccharides, peptides, vitamins, and pigments, which contribute to cellular defence mechanisms against oxidative damage. However, fish are generally unable to access intracellular antioxidant compounds in macroalgae due to the absence of specific enzymes required to degrade complex cell wall polysaccharides. One strategy to overcome this limitation involves the use of pretreated seaweed biomass. The dietary inclusion of high-solid-loading pretreated Codium tomentosum was evaluated in juvenile European seabass (Dicentrarchus labrax) over an 11-week feeding trial. Alkaline pretreatment (30 or 60 min) under high-solid-loading conditions mitigated the effects associated with dietary inclusion of C. tomentosum, reducing markers of intestinal oxidative damage and positively modulating basal immune responses, without significantly altering intestinal microbial diversity [Contribution 5].

In conclusion, recent advances in aquaculture nutrition, such as those published in this SI, emphasise the importance of feed formulation and functional additives in enhancing the health, performance, and welfare of farmed aquatic species. The incorporation of innovative nutritional strategies, such as probiotics, trace element enrichment, seaweeds, and alternative protein sources, holds considerable promise for improving growth efficiency, immune function, and the overall nutritional value of aquaculture products. Furthermore, these approaches support the sustainability of aquaculture by reducing environmental impacts, optimising feed utilisation, and promoting the development of resilient and efficient production systems. Continued research in aquafeed innovation not only addresses the specific nutritional requirements of different species but also aligns with consumer expectations and public health considerations. The ongoing application of nutritional engineering in aquaculture is therefore pivotal for producing high-quality, sustainable, and nutrient-rich aquatic foods to meet the demands of a growing global population.

This Special Issue, Pivotal Roles of Feed Additives for Fish, of Fishes was made possible through the collective efforts and dedication of the entire editorial team. I would like to convey my sincere appreciation to all those involved for their hard work and commitment.