Natural abundance of ¹⁵N and ¹³C in fish tissues and the use of stable isotopes as dietary protein tracers in rainbow trout and gilthead sea bream
BELTRÁN, M. | FERNÁNDEZ-BORRÁS, J. | MÉDALE, F. | PÉREZ-SÁNCHEZ, J. | Kaushik, S. | BLASCO, J.
For developing efficient diets, two sets of experiments examined whether the use and allocation of dietary protein can be traced by labelling with stable isotopes (¹⁵N and ¹³C) in two culture fish (Oncorhynchus mykiss and Sparus aurata). In the first experiment, natural abundance and tissue distribution of these isotopes were determined, by measuring the δ¹³C and δ¹⁵N values by isotopic ratio mass spectrometry, in fingerlings (14-17 g) adapted to diets differing in the percentage of fish meal replacement by plant protein sources. For both species, δ¹⁵N and δ¹³C were greater in tissues with higher protein and lower lipid content. Delta ¹⁵N of diets and tissues decreased as replacement increased, suggesting δ¹⁵N can be used as a marker for dietary protein origin. The ¹⁵N fractionation (δ¹⁵N fish - δ¹⁵N diet) differed between groups, and could thus be used to indicate protein catabolism. In the second experiment, fish (75-90 g) of each species ingested a diet enriched with ¹⁵N-protein (10 g kg⁻¹ diet) and ¹³C-protein (30 g kg⁻¹ diet). These proportions were suitable for determining that the delta values of tissue components were high enough above natural levels to allow protein allocation to be traced at 11 and 24 h after feeding, and revealed clear metabolic differences between species.
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