The study investigated organic acids and organic acid salts as growth promoters in cultured South African abalone Haliotis midae when incorporated as feed additives in formulated feed. Two blends of organic acids (1% acetic acid+1% formic acid, and 1% benzoic acid+1% sorbic acid) and one of organic acid salts (1% sodium benzoate+1% potassium sorbate) were evaluated in South African abalone (23mm initial mean length), and tested against a negative control and positive control containing 30ppm avilamycin as antibiotic growth promoter (AGP). Experiments were performed at controlled water temperatures under optimal (Phase 1) and sub-optimal (Phase 2) temperatures. During Phase 1 the organic acid and organic acid salt blends significantly enhanced mass growth rate (both linear weight increase [AGRW] and specific growth rate [SGR]) compared to both controls. Linear length increase (AGRL) was significantly higher than the negative control. SGR was increased by 15.8%–17.9% relative to the negative control; AGRW and AGRL were between 12.9%–22.9% and 11.7%–13.5% higher, respectively. No significant growth enhancement was observed during Phase 2. Avilamycin had no effect on growth and none of the treatments had significant effects on feed conversion ratio (FCR), relative incidence cost (RIC, relative to negative control) or feed intake during either phase. The mode of growth enhancement could not be established; it could not be shown that the acid and salt treatments or the AGP had any effects on intestinal microflora, but possible energy effects of the acids were eliminated as potential mechanism; it is unclear what role gut acidification played in the enhanced growth performance.