Figure 1.

Diagram showing the importance of trypsin for a series of growth mechanisms through its role as the key enzyme in protein digestion process. Trypsin expression and the protease activity ratio of trypsin to chymotrypsin (T/C ratio) in the pyloric caeca, affecting nutrient influx that subsequently influences capacity for protein synthesis and immune system and growth, is influenced by temperature and dietary quality (Rungruangsak Torrissen and Male 2000; Sunde et al. 2004; present work) as well as by light regime (Sunde et al. 2001), growth hormone (Lemieux et al. 1999), gene manipulation (Sunde et al. 2001; Blier et al. 2002), and by vaccine type (unpublished work). Transport rate and level of free amino acids to target tissues (affecting plasma insulin secretion and protein synthesis in the white muscle) indicate protein utilisation efficiency and flesh quality of the fish. Details of the effects of trypsin expression on protein utilisation and muscle capacity for protein synthesis and on growth were described in Rungruangsak Torrissen and Male (2000) and Sunde et al.