The availability of high quality water source enables construction of a fish farm based on a flow through or recirculating aquaculture systems (RAS). The trend in Slovenia is to use flow through systems; however, recently an increase in use of RAS was noticed. Financially speaking flow through systems are cheaper than RAS, but on the other hand RAS enables higher production at the same quantity of used water. Further advantages of RAS can be observed in better and easier monitoring of the water parameters such as oxygen, CO2, pH levels and the level of nitrates etc. as well as in lesser negative environmental impact. The dimensions of fish farm are results of a study complexity of the system which is based on several conditions where the water treatment technology, fish breeding conditions and feeding strategy are the most important. The diploma task presents the design of flow through and recirculation fish farm for salmonid fish. The first model with flow through system is identified maximum capacity of fish breeding and quality of discharge water. The second model uses RAS. In this case the quality of process and outlet water has to be checked for certain breeding capacity in order to establish what water treatment system should be designed in order to enable water to be reused as many times as possible and for the water that does not meet the quality criteria to be released back to nature.