Abstract: Disclosed are pellets for use in a fluidized bed type of system to provide optimum surface configuration and maximum effective surface area per unit volume for the culture of microorganisms. The pellets are of low density, preferably plaster, having a buoyancy relative to the liquid in which they are fluidized substantially neutral or slightly positive. The pellets preferably have indentations on its surfaces to enhance the growth of microorganisms. The pellets are manufactured by either cutting discs from an extruded filament or punching discs from sheets of the appropriate material, with indentations being formed during the process.Also disclosed is an aquaculture apparatus and system in which the pellets are preferably used.