*3.2.2. Fungi*

Fungi are a group of eukaryotic organisms that include unicellular microorganisms, such as yeasts and molds, as well as multicellular fungi. Most yeasts reproduce asexually by mitosis and many others by the asymmetric division [38]. Typically measuring 3–4 μm in diameter, they are widely distributed in freshwater and saltwater (*Candida*, *Cryptococcus*, *Rhodotorula*, and *Debaryomyces*). Some marine species live at temperatures as low as −13° and at deeps of 4000 m; some others can nearly saturate brine solutions. Seawater normally contains 10–100 yeast L−1, but in estuarine environments, the number significantly increases [39]. Brown et al. [33] evaluated seven species of yeast to determine their nutritional value and found 25–37% of protein, 21–39% of carbohydrate, and 4–6% of lipid, as well as complete profile of essential amino acids. Yeasts are strictly chemoorganotrophic and require organic forms of carbon which are quite diverse and include sugars, polyols, organic and fatty acids, aliphatic alcohols, and various heterocyclic and polymeric compounds [39].

Fungi, especially yeast (chemoorganotrophic microorganisms), are also reported in biofloc. They use organic compounds as a source of energy. Carbon is obtained mostly from hexose sugars, such as glucose and fructose. In a biofloc culture of tilapia, Monroy-Dosta et al. [40] reported the presence of the yeast *Rhodotorula* sp. during the fifth week, which increases its biomass by the end of the culture period.
