The growth properties of juvenile spotted wolffish Anarhichas minor reared at 4, 6, 8 and 12° C, and a group reared under ‘temperature steps’, (T-step)i.e. with temperature reduced successively from 12 to 9 and 6° C were investigated. Growth rate and feed efficiency ration was significantly influenced by temperature and fish size. Overall growth rate was highest at 6° C (0·68% day−1) and lowest at 12° C (0·48% day−1), while the 4 and 8° C, and the T-step groups had similar overall growth rates, i.e. 0·59, 0·62 and 0·51% day−1 respectively. Optimal temperature for growth (Topt G) and feed efficiency ratio (Topt FCE) decreased as fish size increased, indicating an ontogenetic reduction in Topt G and Topt FCE. The results suggest a Topt G of juvenile spotted wolffish in the size range 135–380 g, dropping from 7·9° C for 130–135 g to 6·6° C for 360–380 g juveniles. The Topt FCE dropped from 7·4° C for 120–150 g to 6·5° C for 300–380 g juveniles. A wider parabolic regression curve between growth, feed efficiency ratio and temperature as fish size increased, may indicate increased temperature tolerance with size. Individual growth rates varied greatly at all time periods within the experimental temperatures, but at the same time significant size rank correlations were maintained and this may indicate stable size hierarchies in juvenile spotted wolffish.