A multi-tracer approach using stable isotopes and elements to assess provenance of Arapaima gigas

Commercially valuable fish face intense pressure from capture fisheries with demand for fish protein, whether farmed or wild-caught, growing globally. Consequently, the provenance of fish is increasingly vital to regulatory bodies, market chain actors, and consumers. The limitations of current fish provenance methods can be overcome using complementary techniques. Here, we applied a multi-tracer approach combining stable isotope ratios (δ¹³C and δ¹⁵N) and trace element mass fraction to assess the provenance of the Amazonian pirarucu (Arapaima gigas) in Brazil. Dorsal muscle samples from 79 individuals of known origin and management were analysed, including wild-caught fish from the Amazon and Tocantins-Araguaia river basins and farmed fish from intensive aquaculture systems. To evaluate the method under real market conditions, additional 52 samples obtained from commercial establishments in the Brazilian Federal District were included. Stable isotope analysis effectively differentiated management regimes and river basins, with δ¹³C providing the strongest discrimination. Trace element analysis revealed significant differences in cesium (Cs) and strontium (Sr) mass fractions between wild fish from the two basins, reflecting underlying geological and hydrological contrasts. Linear discrimination analysis (LDA) integrating isotopic and elemental data demonstrated a high discriminatory capacity of both isotopic and elemental tracers for distinguishing pirarucu samples according to origin and management category. Although the reference groups showed complete discrimination under cross-validation, commercial samples displayed broader dispersion within the discriminant space, suggesting heterogeneous sourcing patterns and potentially mixed supply chains. These findings demonstrate that the combined use of isotopic and elemental tracers offers a robust framework for assessing the provenance of freshwater fish and represents a valuable tool for fisheries monitoring and the enforcement of conservation measures.