Abstract
Aquafeed accounts for at least 75–90% of aquaculture’s operating costs. Traditional aquafeed ingredients such as fishmeal, fish oil, and soybean meal are unsustainable; further, their increasing cost necessities developing alternative feed ingredients. Microalgae-based aquafeed is not only environmentally friendly, but it can also be cost-effective with proper optimization. In addition, the nutrition profile of microalgae is similar to that of many fishes. The digestibility of a feed is one of the most important factors to consider in feed formulation. A highly digestible feed can lower production costs, reduce feed waste, and reduce the risk of eutrophication. This review discusses the digestibility of various nutrients such as protein, lipid, carbohydrate, amino acids, and fatty acids (including omega-3 fatty acids), dry matter, and energy of various microalgae in fish. Other commonly used aquafeed ingredients were also compared to microalgae in terms of nutrient and energy digestibility in fish. The intrinsic characteristics of microalgae, biomass pretreatment, and feed preparation methods are all discussed as factors that contribute to the nutrient and energy digestibility of microalgae in fish. Furthermore, methods for increasing the digestibility of microalgal biomass in fish are suggested. Finally, the review concludes with the challenges and prospects of using microalgae as a fish feed in terms of digestibility.
Highlights
This review summarizes the nutrient and energy digestibility of various microalgae in fish
The digestibility of protein for Schizochytrium sp., Isochrysis sp., Spirulina sp., Chlorella vulgaris, Nannochloropsis oceanica, and Nannochloropsis oculata was found to be higher than 80% in fish such as rainbow trout (Oncorhynchus mykiss), Nile tilapia (Oreochromis niloticus), European seabass (Dicentrarchus labrax), and African catfish (Clarus gariepinus) (Table 1)
In another study, the enzymatically processed Nannochloropsis oceanica had 11% higher energy digestibility than the same microalgae that had been treated with bead milling for European seabass juveniles (Dicentrarchus labrax) [34]
Summary
Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. The nutritional content of microalgae is of limited use in feed formulation because it does not provide information on the hydrolytic products available for growth after digestion [4]. This could be known through digestibility studies. Apart from fishmeal, commonly found ingredients in aquafeed are plant-based ones, including soybean meal, groundnut cake, rice bran, wheat gluten, wheat middlings, corn starch, and palm oil. Diets are formulated based on crude energy and nutrients due to a lack of proper information about a new ingredient’s digestibility From this perspective, this review summarizes the nutrient and energy digestibility of various microalgae in fish. Factors affecting microalgae digestion in fish as well as methods to improve microalgae digestibility in fish are discussed
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