This article discusses the types of deheading cuts used in fish processing. The cutting strength of deheading was also analyzed. Based on the potential stiffness difference of fish tissues, it was revealed that by steering the relief angle of the blade to the cut surface it is possible to make an efficient deheading V-cut with one knife instead of the two circular knives that have been used to date. The results of the theoretical analyses were confirmed by a study which was preformed on different tissue samples - the stiffness of backbone is 994 times bigger than the stiffness of muscle tissue measured in comparable conditions. This allows to construct a simple V-cutting deheading machine with one knife. (c) 2007 Elsevier Ltd. All rights reserved.