# Microalgae: Potential for Bioeconomy in Food Systems
## 4 Animal Feed  
Some microalgal species have been used in animal feed, aquaculture, and beekeeping owing to their bioactive compound content [51, 52, 53]. The source of microalgal biomass can be either cultures destined to produce nutritional supplements or residual biomass from pollutant-free industrial processes, such as biofuel production [54, 55, 56, 52]. In pig farming, the use of biomass supplements or microalgae oils has been shown to strengthen the immune system and improve animal health, thus enhancing the sensory characteristics and lipid composition of the meat [15, 57, 51, 58]. Nutrition in pregnant sows and fattening pigs could be optimized using species such as _C. vulgaris_, _Arthospira_ sp., _Aurantiolytrium limacinum_, and _Desmodesmus_ sp. ; in addition, production increases and the composition of fatty acids in meat improves, thus increasing the DHA content [57, 59, 60]. In ruminants, food supplementation with meal or oil from some species of microalgae has been explored [51, 61, 62]. As a result, improved organoleptic properties and fatty acid composition of meat and milk were observed in bovines [63, 64, 65]. Microalgae, such as _A. platensis_, were shown to be a good replacement for plant supplements, and improving the quality of milk [66]. Nevertheless, different species and concentrations need to be studied in bovines to avoid possible alterations in the organoleptic characteristics of meat [56, 67]. In sheep, supplementation with _A. platensis_ increased growth and development of animals, and _Schizochytrium_ sp. improved meat quality [68, 69]. Extracts from _C. sorokiniana_ and _D. tertiolecta_ exerted positive effects on anti-inflammatory activity and immunomod, enabling reduction in the use of antibiotics in pregnant or postpartum females [70, 71]. Finally, supplementation with _C. vulgaris_ in the diet of goats reduces oxidative stress, improving the quality of the milk since it has greater stability and better organoleptic characteristics [72]. In chickens and hens, food supplementation with microalgae has also shown beneficial effects on animal health and meat and egg production [15, 51]. For instance, improved growth and meat quality, as well as a decrease in chronic diseases in broiler chickens, were observed after supplementation with _C. vulgaris_, _A. platensis_, _Starosira_ sp., _Schizochytrium_ sp., _Aurantiochytrium_ sp. and _Amphora coffeaferminis_[51; 73; 74; 75; 76]. In laying hens, supplementation with _A. platensis_, _Nannochloropsis gaditana_, and _Porphyridium_ sp. improved animal nutrition and health, as well as reduced cholesterol levels and enhanced organoleptic properties of the eggs [77; 78; 73]. Positive effects have also been observed in rabbits. _C. vulgaris_ and _N. oceanica_ improved the health, growth, and meat quality of animals [79; 80]. The enormous potential of microalgae has also been studied in bees. The productivity, physiology, and health of honeybees improved when fed with microalgae [53]. In 2018, fish farming production accounted for 271,610 million USD and is estimated to generate 376,480 million USD by 2025. Therefore, the production of fish, crustaceans, mollusks, and algae is one of the most promising industries, with algae being extremely valuable [81]. Microalgae are essential in the feeding of aquatic animals [52]. The implementation of microalgae in fish farming is an environmentally friendly alternative to the non-sustainable fishmeal and fish oil-based feeds currently used. Microalgae have been successfully tested in salmon, trout, tilapia, ornamental fish, and crustaceans [51; 82]. In farmed shrimp, feeding with _T. chuii_, _Dunialella_ sp., _A. platensis_, _Hypnea cervicornis_, and _Cryptonemia crenulata_ improved both immunity and production [52; 83]. Salmon and carp fed with _Nanofrustulum_ sp., _Tetraselmis_ sp., and _Haematococcus pluvialis_, and tilapia fed with _N. oculata_, and _Schizochytrium_ sp. showed improved health and higher nutritional value compared to the meat [84; 85; 86; 82].