Improving estimates of trophic shift (Δδtrophic) for diet reconstruction studies using enzyme activities

For diet reconstruction studies using stable isotopes, accurate estimates of trophic shift (Δδtrophic) are necessary to get reliable results. Several factors have been identified which affect the trophic shift. The goal of the present experiment was to test whether measurements of the activities of enzymes could improve the accuracy of estimation of trophic shift in fish. Forty-eight Nile tilapia (Oreochromis niloticus) were fed under controlled conditions with two diets differing in their protein content (21 and 41%) each at four different levels (4, 8, 12 and 16 g kg− 0.8 d− 1). At the end of the feeding experiment, proximate composition, whole body δ13C and δ15N as well as the activities of enzymes involved in anabolism and catabolism were measured. Step-wise regression specified contributing variables for Δδ15N (malic enzyme, aspartate aminotransferase and protein content) and Δδ13Clipid-free material (aspartate aminotransferase and protein content). Explained variation by using the significant main effects was about 70% for Δδ15N and Δδ13Clipid-free material, respectively. The results of the present study indicate that enzyme activities are suitable indicators to improve estimates of trophic shift.