A fluidized bed filter is described and claimed. The filter is exemplified for use in an aquaculture system under hydraulic pressure. A preferred embodiment of the filter of the subject invention comprises a closed cylinder having an inlet port and an outlet port at or near one end. Water is pumped into the inlet port and through a hollow delivery tube positioned within the cylinder and ending a short distance from the closed end of the cylinder. The force of the water contacting the closed end of the cylinder causes the water to change direction drastically creating a flow pattern within the cylinder. This flow pattern exerts a force sufficient to fluidize filter medium within the cylinder. Filtered water escapes the system via the outlet port.