Microalgae are photosynthetic microorganisms, whose size are between 2–200 µm, however they can grow autotrophically or heterotrophically. There are many types of organization: unicellular, filamentous or colonial. Cells can have external structures such as membranes, cell walls or silica exoskeletons (Randrianarison and Aqeel Ashraf 2017). These organisms are the simplest of the plant kingdom with a great capacity to adapt to different environments, they use the energy of light and can fix carbon dioxide (CO2) more efficiently than land plants, so they produce more quantities of biomass (Christaki et al. 2011; Gaignard et al. 2018). Currently, there are more than 100,000 species identified (Guiry et al. 2014) that live in almost all environments and are distributed around the world (Posten and Feng 2016; Geada et al. 2017).
The first records about the use of microalgae as food were around 2000 years ago, when Chinese people used the Nostoc genus to alleviate the famine of their people. Another reference on the application of microalgae in nutrition is associated with the treatment of patients with leprosy, who were included in their diet a soup enriched with Chlorella sp. and it was observed that they had an increase in their weight, energy and general health (Milledge 2011; Sigamani et al. 2016). The culture of microalgae began to be developed in Japan as a solution to the food shortage caused by the Second World War and there was a development of products enriched with microalgae. Thenceforth, many studies about biomass production have focused on obtaining biofuels, wastewater treatment and as a high protein food source for use in humans and animals, especially in aquaculture (Spolaore et al. 2006; Christaki et al. 2011; Yaakob et al. 2014; Garcia et al. 2017; Koyande et al. 2019).
Several studies have shown that microalgae can represent an attractive source of compounds with biological activity. For example, polyunsaturated fatty acids (PUFA), carotenoids, phycobilins, peptides and polysaccharides. In addition, they are a good source of A, B1, B2 and B12 vitamins (Skjånes et al. 2013; De Morais et al. 2015). Currently, several products are marketed in the form of tablets, powder, solution or in mixtures with snacks, cookies, noodles, drinks, candies, gums, wines and cereals (Sathasivam et al. 2017; Levasseur et al. 2020). The main countries that lead the world production are China, India, Taiwan, Germany and a few in Latin America (Koyande et al. 2019; Levasseur et al. 2020).
There are two well-known genus: Arthospira (commercially known as Spirulina) and Chlorella, both with a production of 12000 and 5000 tons per year, respectively. In last decades, many researchers have studied other species and produce biomass such as Haematococcus, Dunaliella, Botryococcus, Phaeodactylum, Porphyridium, Chaetoceros, Crypthecodinium, Isochrysis, Nannochloris, Nitzschia, Schizochytrium, Tetraselmis and Skeletonema. (Plaza et al. 2009; Sathasivam et al. 2017; Matos et al. 2017, Levasseur et al. 2020). However, only a small percentage of all species with potential has been studied. In the same way, research about the development of organoleptically acceptable products, their compounds, benefits, isolation techniques, performance improvement, determination of their bioactivity and toxicity are still scarce (Stengel et al. 2011; Buono et al. 2014; Levasseur et al. 2020).
In aquaculture, the protein supplied in the food of aquatic organisms comes from fishmeal; this ingredient increases its price due to the high demand worldwide and its limited production by fisheries (Amaya et al. 2007; FAO 2018; FAO 2020). As an alternative solution, new commodity markets have been developed such as high-quality processed animal by-products (hydrolyzed feather meal, blood meal, meat and bone meal), vegetables flour, protein concentrates obtained from oilseeds and legume grains. Similarly, it is known that in salmonid farming, fish oil in feed has been replaced by other fats of animal and vegetable origin, although these "second generation" ingredients are not without limitations (Hua et al. 2019).
This sector needs to grow, so several institutions have begun to investigate the use of "third generation ingredients", which is defined as ingredients that come from lower trophic levels (Shah et al 2018; Glencross et al. 2020). In this manner, microalgae biorefineries emerge as an option. There is an advantage in the reuse of industrial emissions, since their waste “outlets” (CO2, nutrients, heat) turn out to be the essential “inputs” for the microalgal culture, which would allow achieving rapid cell growth and a greater accumulation of biomass. In terms of input costs, microalgae-based ingredients produced for aquafeeds could have competitive advantages over terrestrial crops, due to it uses lower crop area, potential for wastewater remediation and carbon credits from CO2 conversion (Roy and Pal 2014, Allen et al. 2019; Perez-Velazquez et al. 2019; Levasseur et al. 2020).
Research in the field of microalgae has increased, which shows its potential. In Peru, studies on massive culture of native microalgae are scarce, therefore, it is important to investigate the biotechnological uses of microalgae in different industries such as in aquaculture, food, pharmaceuticals, renewable energy and others. For this reason, the present study evaluated the culture of the native microalgae Desmodesmus asymmetricus in greenhouse conditions, the aim was to determine the values of biomass productivity, protein and amino acids concentrations and its potential as ingredient in aquaculture industry.