The effects of temperature on growth and survival of juvenile blackfoot abalone, Haliotis iris, were investigated. Animals of 10, 30 or 60 mm initial shell length were exposed to ambient (6–10°C), 14, 18, 22 and 26°C for 112 days in a flow-through culture system. Maximum growth occurred at 22°C for the 10 and 30 mm size classes and at 18°C for the 60 mm size class. Regression analysis identified the optimal temperature for growth (ToptG) at around 21°C for the 10 and 30 mm size classes and at 17–18°C for the largest size class. In a second experiment, the critical thermal maximum of H. iris was determined as a measure of thermal tolerance. Abalone were subjected to increasing water temperatures at a rate of 2°C h−1 until they detached from the substrate. Abalone of 10 mm displayed greater thermal tolerance than abalone of 30 and 60 mm in length. CT50 temperatures were 28.8, 27.7 and 27.8°C, yielding deduced ToptG values of 19.7, 18.3 and 18.4°C for the 10, 30 and 60 mm size classes respectively. The size-dependent nature of the relationship between growth and temperature could be capitalized upon in recirculating aquaculture systems.