Abstract Critical concentrations of tissue nitrogen and phosphorus for growth rate and yield in the freshwater blue-green alga Microcystis aeruginosa Kütz. were investigated to facilitate its production in aquaculture ponds. Growth-curve and yield experiments in flask cultures of Microcystis confirmed earlier predictions of reductions in assessed yield-derived critical concentrations caused by culture-ageing effects. Yield-derived critical levels for 90% saturated response were 4.1% N and 0.28% P. A derivation which assumed a Droop equation parameterization of growth enabled conversion of the yield-derived values to growth-rate critical concentrations. For 90% saturated growth rate these were N ≤ 5.4% and P ≤ 0.42%. Field and culture pond measurements commonly found in excess of these values and the well-known ability of algae to remove nutrients from water indicate that fertilizer applications sufficient to maintain tissue levels in excess of the critical levels would be an efficient strategy for maximum Microcystis production in culture ponds.