Different expressions of trypsin and chymotrypsin in relation to growth in Atlantic salmon (Salmo salar L.)

Abstract

The expressions of trypsin and chymotrypsin in the pyloric caeca of Atlantic salmon (Salmo salar L.) were studied in three experiments. Two internal (trypsin phenotypes, life stages) and three common external factors (starvation, feeding, temperatures) influencing growth rates were varied. Growth was stimulated by increased temperature and higher feeding rate, and it was depressed during starvation. The interaction between trypsin phenotype and start-feeding temperature affected specific activity of trypsin, but not of chymotrypsin. Trypsin specific activity and the activity ratio of trypsin to chymotrypsin (T/C ratio) increased when growth was promoted. Chymotrypsin specific activity, on the other hand, increased when there was a reduction in growth rate whereas fish with higher growth had higher chymotrypsin specific activity resulting in lower T/C ratio value. During a rapid growth phase, trypsin specific activity did not correlate with chymotrypsin specific activity. On the other hand, a relationship between specific activities of trypsin and chymotrypsin could be observed when growth declined, such as during food deprivation. Trypsin is the sensitive key protease under conditions favouring growth and genetically and environmentally affected, while chymotrypsin plays a major role when growth is limited or depressed. Trypsin specific activity and the T/C ratio value are shown to be important factors in the digestion process affecting growth rate, and could be applicable as indicators for growth studies of fish in captive cultures and in the wild, especially when food consumption rate cannot be measured.

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growth hormone (Lemieux et al. 1999), gene manipulation (Sunde et al. 2001; Blier et al. 2002), and by vaccine type (unpublished work).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.

Figure 2

Effect of starvation on expressions of pepsin, trypsin, and chymotrypsin in the digestive tract of Atlantic salmon. Arrows with probability values indicate first observations of significantly changing in the enzyme expressions. The values with asterisk (*) are significantly different (p<0.05). The enzyme specific activities are expressed as µmol tyrosine h⁻¹ mg protein⁻¹ for pepsin in the stomach, and as µmol p-nitroaniline h⁻¹ mg protein⁻¹ for trypsin and chymotrypsin in the pyloric caeca.

Figure 3

Relationships of weight with trypsin, chymotrypsin, and with the activity ratio of trypsin to chymotrypsin (T/C ratio) during the first winter in Atlantic salmon parr, regardless of rearing temperatures and trypsin phenotypes. The enzyme specific activities of trypsin and chymotrypsin are expressed as µmol p-nitroaniline h⁻¹ mg protein⁻¹.

Figure 4

Effects of water temperature and routine feeding on the relationships of trypsin with chymotrypsin and with the activity ratio of trypsin to chymotrypsin (T/C ratio) in Atlantic salmon parr reared at 6 °C (×) and 10 °C (D), regardless of trypsin phenotypes (a) and (b), and according to trypsin phenotypes at 6 °C (c) and 10 °C (d). The enzyme specific activities of trypsin and chymotrypsin are expressed as µmol p-nitroaniline h⁻¹ mg protein⁻¹. ns, not significant.

Figure 5

Effects of temperature and post-feeding on the relationships of trypsin with chymotrypsin and with the activity ratio of trypsin to chymotrypsin (T/C ratio) in Atlantic salmon parr reared at 6 °C (×) and 10 °C (D), regardless of trypsin phenotypes (a) and (b), and according to trypsin phenotypes at 6 °C (c) and 10°C (d). The enzyme specific activities of trypsin and chymotrypsin are expressed as µmol p-nitroaniline h⁻¹ mg protein⁻¹.