# A Review on the Use of Microalgae for Sustainable Aquaculture
## 3 Microalgae-Assisted Aquaculture
### Technologies for Biomass Harvesting
#### 3.4.2 Fungi-Assisted Harvesting  
Fungi-assisted microalgae harvesting refers to the addition of filamentous fungi, including either fungal pellets or fungal spores, into medium with microalgae. The study of [PERSON] et al. (2013) found that that microalgae cells could attach to or be entrapped in the fungal pellets, which could be harvested by simple filtration. It was discovered that the use of fungal pellets could harvest over 95% of microalgae biomass in 1.5 h, revealing the great performance of fungi in microalgae harvesting [67]. In practice, however, the production of fungal pellets has a strict requirement on equipment and fermentation conditions, which increase the total cost of harvesting. Recently, to further simplify the harvesting procedure, the co-cultivation of fungal spores with microalgae in wastewater or medium has been intensively studied. In some cases, the co-cultivation will not only harvest microalgae biomass, but also promote the nutrients recovery from aqueous phase, which has been fully confirmed by the study of [PERSON] et al. (2014) that co-cultivated _Aspergillus_ sp. with _Chlorella_ sp. in molasses wastewater. According to previous studies, the parameters that impact the fungal-algal pellet formation and determine the pellet size include inoculation ratio of fungi/algae, pH value, carbon content, cultivation temperature, and so on [67; 68; 69]. Table 3, which lists some examples of fungi-assisted microalgae harvesting, confirms that it is an efficient way to collect biomass from culture medium or wastewater by employing fungal spores or fungal pellets. For aquaculture practice, fungi used for microalgae harvesting should have a high safety level, meaning that they do not contain or secrete toxic components. Otherwise, harvested biomass used as aquaculture feed may threaten the survival of aquatic animals or even lead to the failure of aquaculture. Some fungal strains, such as _Aspergillus oryzae_ and _Monascus purpureus_, isolated from food production have a high safety \begin{table}
\begin{tabular}{c c c c} \hline \hline  & **Harvesting Cost** & **Safety Level** & **Time Consumption** \\ \hline \multirow{3}{*}{Centrifugation} & High (Energy-intensive & \multirow{3}{*}{High} & \multirow{3}{*}{Short} \\  & centrifugation & & \\  & equipment) & & \\ \hline \multirow{3}{*}{Filtration} & High (Frequent & \multirow{3}{*}{High} & \multirow{3}{*}{Short} \\  & replacement of filter & & \\  & blocked by algal cells) & & \\ \hline \multirow{3}{*}{Gravity-driven sedimentation} & \multirow{3}{*}{Low} & High & Long (Repulsive force \\  & & & among negatively charged \\  & & & algal cells) \\ \hline \multirow{3}{*}{Flocculation by chemicals} & \multirow{3}{*}{Low} & Low (Addition of toxic & \multirow{3}{*}{Short} \\  & & or unhealthy chemicals) & \\ \hline Harvesting by edible fungi & Low & High & Short \\ \hline Flotation & Low & High & Short \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Comparison of harvesting technologies for aquaculture. level and contain value-added compounds [69; 70]. However, beneficial effects of these fungi on aquatic animals have not attracted attention from researchers yet. In addition to the simplification of the harvesting process, co-cultivation of fungi with microalgae could promote nutrients recovery from aquaculture wastewater with high contents of solid organics. Previous work, which presented the metabolic mechanisms of fungi and microalgae, showed that fungal cells could convert high-molecular-weight organics to low-molecular-weight organics easily utilized by microalgal cells in the co-cultivation system [69]. At the same time, carbon dioxide released by fungi through heterotrophic metabolism could be assimilated by microalgae through photosynthesis, preventing the greenhouse gas emission and improving the carbon utilization efficiency. Such a synergistic relationship between microalgae and fungi has been proven by the study of [PERSON] et al. (2014).