Overpopulation and lack of resources have become serious problems in recent years. Therefore, there is an urgent need to find renewable sources of food to confront this problem. Aquaculture is an inexpensive and important source of protein, as aquaculture have increased significantly, especially during the past two decades. The wastewater produced from those farms includes many harmful elements such as ammonia (NH3), organic matter (OM), phosphorous(P) and dissolved organic carbon (DOC). So, it has become necessary to find an appropriate method to treat the wastewater produced from those farms. There are many ways to treat wastewater from fish farms, including physical, chemical or biological methods. Biological treatment is one of the best methods used in wastewater treatment from aquaculture, as it is environmentally friendly and less expensive than other methods. The biofiltration process depends on the use of microorganisms that convert ammonium (NH4+) to nitrite (NO2-) and then to nitrate (NO3-), and this is done using a Recirculating Aquaculture Systems (RASs). The main component of the biofilter is the filter media, which can be compost, wood chips, beads, other organic or inorganic materials. There are many types of microorganisms used to treat wastewater like Microalgae, bacteria, fungi, yeast. The choice of the type of microorganism used depends on the chemical nature of the pollutants.