*3.2.4. Zooplankton*

*3.2.2. Fungi*

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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,

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

Photoautotrophic community (microalgae) also play an important role in the biofloc system. Microalgae assimilate mainly ammonia and nitrate to produce biomass, additionally consume carbon dioxide, and produce oxygen. The divisions of microalgae reported in biofloc cultures are Chlorophyta, Chrysophyta, and Cyanophyta. These microorganisms catch the solar energy,

In biofloc cultures the microalgae can live as free cell into the water column or could form aggregates. In some cases the aggregations of chrysophytes and cyanophytes can measure up to 2 mm in diameter [41]. Their sizes are highly variable, with cells of less than 10 μm to

Chlorophytes are green microalgae that are the most numerous and diverse in the freshwater; they can reproduce massively forming blooms, but, at difference of the cyanophytes, are nontoxic. This division presents a high plasticity and is able to colonize diverse habitats; they are

Chrysophytes are the most representative organisms that correspond into the Bacillariophyceae class (diatoms), which is divided in centric and pennate. The planktonic species are mainly centric; meanwhile, the pennate are commonly benthic. All centric species are marine, while most of the pennate live in freshwater [43]. In aquaculture, diatoms are considered as beneficial algae because they are a source of food and nutrients for most aquatic animals [44].

Cyanophytes are known as the most ancient photosynthetic organisms; they possess a high morphologic and structural variability. During its evolution they have developed various

to produce chemical energy (carbohydrates), which is used in their metabolic process.

aliphatic alcohols, and various heterocyclic and polymeric compounds [39].

biomass by the end of the culture period.

spherical or oblong and may have flagella or not [43].

*3.2.3. Microalgae*

more 50 μm [42].

Protozoa is one of the most relevant microorganism groups in BFT system. They play an essential role (together with bacteria) recycling the organic matter in the system. Both groups are the "basis" of the trophic transfer of energy to the next levels. Protozoa have different body shapes (spherical, oval, and elongated) and often have one or more whip appendages called flagella or many short hair-like structures called cilia. Protozoa are abundant in many types of environments and often are found on the surfaces of submerged rocks, free living into the water column or colonizing the sediment. Ciliates are the largest group of protozoa in nature; they eat bacteria (including cyanobacteria) and small phytoplankton. Some are carnivorous and feed on zooplankton [53].

In nature, ciliates have importance as a live food source for juvenile stages of aquatic animals including small invertebrates. Pandey et al. [54] carried out the analysis of the ciliate *Fabrea salina* to evaluate proximate and biochemical composition. The moisture, protein, fat, carbohydrate, and ash content from natural sources were 86.66%, 56.66%, 36.66%, 1%, and 4%, respectively. Gas chromatographic analysis revealed the presence of fatty acids such as oleic, palmitic, palmitoleic, linoleic, and stearic.

Ballester et al. [14] registered concentrations from 39 to 169 ciliates/mL, in postlarvae *Farfantepenaeus paulensis* biofloc culture. Maicá et al. [52] found an average concentration of 164, 64, and 29 ciliates mL−1 in water salinities of 2%, 4%, and 25%, respectively. Furthermore, Monroy-Dosta et al. [40] observed minimum and maximum concentrations of 13 and 39 and also noted a variation in species according to the culture age.

Rotifer belongs to the smaller group of metazoans. Most rotifers are 0.1–0.5 mm long. Their body shape varies widely between groups: they can be spherical, cylindrical, or elongated. The body can be soft or may have a firm covering called lorica. The cilia surrounding a rotifer's mouth form a circle, called a corona or wheel organ. The rapid movements of the cilia create water currents for swimming and feeding [53]. Their diets consist on microalgae, bacteria, yeast, and protozoa [55].

The rotifers are the group of organisms that probably have been largely used to replace *Artemia* as exogenous natural food in larval culture of crustaceans and fish. Campaña-Torres et al. [56] evaluated the proximal composition of the rotifer *Brachionus rotundiformis* cultured in laboratory and reported a dry content of carbohydrate of 15.9–22.7%, lipid 21.4–24.12%, protein 45.7–61.3%, and ash 4.5–4.6%.

Loureiro et al. [57] indicate that rotifers can fragment the flocs and consume bacteria. The mucilage produced by their excretions contributes to new flocs formation [58]. Ballester et al. [14] registered concentrations form 4.6 to 151 org/mL in seawater; besides, Monroy-Dosta et al. [40] reported concentrations between 28 and 96 org/mL in freshwater.

Copepods comprise two main groups: calanoids and cyclopoids. Calanoid copepods have an elongated body and the first pair of antennae is long, whereas cyclopoid have a robust body and a first pair of antennae is short. In general, both use the appendices near the head to create streams to filter or collect food. They feed on bacteria, phytoplankton, detritus, or any other organic material [53].

Farhadian et al. [59] evaluated the proximate composition of copepod *Apocyclops dengizicus* and reported protein levels between 39 and 42% and lipid between 16 and 19%, indicating that nutritional properties varied according to the microalgae used as feed.

Cladocerans posses a body covered by a transparent shell, although it may be yellowish or brown. A pair of appendages called thoracic members are inside the shell, and are important for the capture and transfer of food particles in the mouth. In general, cladocerans eat a wide variety of phytoplankton and suspended matter. They can greatly reduce the abundance of phytoplankton in the water column [53].

in nature; they eat bacteria (including cyanobacteria) and small phytoplankton. Some are car-

In nature, ciliates have importance as a live food source for juvenile stages of aquatic animals including small invertebrates. Pandey et al. [54] carried out the analysis of the ciliate *Fabrea salina* to evaluate proximate and biochemical composition. The moisture, protein, fat, carbohydrate, and ash content from natural sources were 86.66%, 56.66%, 36.66%, 1%, and 4%, respectively. Gas chromatographic analysis revealed the presence of fatty acids such as oleic,

Ballester et al. [14] registered concentrations from 39 to 169 ciliates/mL, in postlarvae *Farfantepenaeus paulensis* biofloc culture. Maicá et al. [52] found an average concentration of 164, 64, and 29 ciliates mL−1 in water salinities of 2%, 4%, and 25%, respectively. Furthermore, Monroy-Dosta et al. [40] observed minimum and maximum concentrations of 13 and 39 and

Rotifer belongs to the smaller group of metazoans. Most rotifers are 0.1–0.5 mm long. Their body shape varies widely between groups: they can be spherical, cylindrical, or elongated. The body can be soft or may have a firm covering called lorica. The cilia surrounding a rotifer's mouth form a circle, called a corona or wheel organ. The rapid movements of the cilia create water currents for swimming and feeding [53]. Their diets consist on microalgae, bac-

The rotifers are the group of organisms that probably have been largely used to replace *Artemia* as exogenous natural food in larval culture of crustaceans and fish. Campaña-Torres et al. [56] evaluated the proximal composition of the rotifer *Brachionus rotundiformis* cultured in laboratory and reported a dry content of carbohydrate of 15.9–22.7%, lipid 21.4–24.12%,

Loureiro et al. [57] indicate that rotifers can fragment the flocs and consume bacteria. The mucilage produced by their excretions contributes to new flocs formation [58]. Ballester et al. [14] registered concentrations form 4.6 to 151 org/mL in seawater; besides, Monroy-Dosta et

Copepods comprise two main groups: calanoids and cyclopoids. Calanoid copepods have an elongated body and the first pair of antennae is long, whereas cyclopoid have a robust body and a first pair of antennae is short. In general, both use the appendices near the head to create streams to filter or collect food. They feed on bacteria, phytoplankton, detritus, or any other

Farhadian et al. [59] evaluated the proximate composition of copepod *Apocyclops dengizicus* and reported protein levels between 39 and 42% and lipid between 16 and 19%, indicating

Cladocerans posses a body covered by a transparent shell, although it may be yellowish or brown. A pair of appendages called thoracic members are inside the shell, and are important for the capture and transfer of food particles in the mouth. In general, cladocerans eat a wide

al. [40] reported concentrations between 28 and 96 org/mL in freshwater.

that nutritional properties varied according to the microalgae used as feed.

nivorous and feed on zooplankton [53].

98 Water Quality

palmitic, palmitoleic, linoleic, and stearic.

teria, yeast, and protozoa [55].

organic material [53].

protein 45.7–61.3%, and ash 4.5–4.6%.

also noted a variation in species according to the culture age.

As the other zooplankton groups, the cladocerans play an important role into the natural food webs. They could supply a high amount of protein into the biofloc cultures. Berberovic [60] evaluated the elemental composition (CHN) of two *Daphnia* species, reporting the following: C, 46.1%; H, 6.5%; N, 9.7%; and ash, 23.8%, which permit to estimate a protein content of 60.6%. This group of organisms was reported in biofloc system by Emerenciano et al. [61]. Moreover, in a postlarvae culture of *L*. *vannamei* reared in zero-water exchange, Ferreira-Marinho et al. [62] reported *Cladocera* abundance from 0.89 to 1.16 ind mL−1 represented by the genus *Bosmina* (0.39–0.53 ind mL−1) and *Daphnia* (0.50–0.69 ind mL−1).

Nematoda is the other essential group in BFT. The body of these organisms is perfectly cylindrical, coated by a relatively thick noncellular cuticles secreted by the underlying epidermis. The cuticle is composed primarily of collagen [63]. They continuously ingest bacteria and other microbenthic organisms; almost all particles which fit into the buccal cavity are ingested, hinting at a selection mechanism based primarily on particle size. Moens and Vincx [64] proposed six major nematode feeding strategies: (a) microvores; (b) ciliate feeders, (c) deposit feeders sensu stricto, (d) epigrowth feeders, (e) facultative predators, and (f) predators.

Ray et al. [50] mentioned that nematodes are an important group in the biofloc systems, whose abundance is determined by the presence of various ciliates that serve as food. In other studies, Monroy-Dosta et al. [40] observed the appearance of nematodes around the fourth week with average of 25 org mL−1 with a maximum of 125 org mL−1, and their abundance were correlated with the ciliates' presence. Loureiro et al. [57] reported the presence of nematodes in the stomach contents of fish grown in the biofloc and suggest that they are a rich source of live food in situ.
