Starvation and low feeding levels result in an enrichment of ¹³C in lipids and ¹⁵N in protein of Nile tilapia <i>Oreochromis niloticus</i> L.

Abstract

The influence of different feeding levels below and slightly above maintenance on whole body δ 13 C and δ 15 N values of Nile tilapia Oreochromis niloticus was examined. The energy budget of each fish was determined by indirect calorimetry. The δ 13 C values of the lipid‐free material of Nile tilapia fed below and slightly above maintenance level did not differ between the feeding groups, but the δ 13 C values in the lipids and the δ 15 N values of the lipid‐free material showed small but significant differences. Those fish with a negative lipid retention had significantly higher δ 13 C values in the lipid fraction compared to fish that synthesized fatty acids. There was a significant negative correlation between the amount of energy metabolized by the fish and both the δ 13 C values in the lipids and the δ 15 N values of the lipid‐free material. Fasting and feeding below the maintenance level may influence the isotopic composition of animals and should therefore be considered in ecological and nutritional studies.