Atlantic salmon (Salmo solar) fillets were partial frozen in an impingement freezer at -30 degrees C and 227 W/m2.K for 2.1 min prior to storage at a superchilling storage temperature of -1.7 +/- 0.3 degrees C for 28 days. The aim of this article is to study the microstructure of the red and white muscles during superchilling process and during superchilled storage. The histology and microscopic analysis of the red and white muscles were carried out. It was found that the size of the ice crystals formed in the red muscles was smaller than those formed in the white muscles. The equivalent diameters of the intracellular ice crystals obtained upon superchilling (day 0) were 17 +/- 2 and 29 +/- 1 mu m for the red and white muscles, respectively. Significant differences were initially observed between the size of the ice crystals formed during the superchilling process and after 1 day of storage. However, after temperature equalisation (day 1), there was no significant change in the size of the ice crystals. (C) 2012 Elsevier Ltd. All rights reserved.