Differentiation of Neotropical Fish Species with Statistical Analysis of Fourier Transform Infrared Photoacoustic Spectroscopy Data

Fourier transform infrared photoacoustic spectroscopy (FTIR-PAS) was applied to nineteen fish species in Brazil's Upper Paraná River basin to identify differences in the structural composition of their scales. To differentiate the species, a canonical discriminant analysis was used to indicate the most important absorption peaks in the mid-infrared region. Significant differences were found in the chemical composition of scales among the studied fish species, with Wilk's lambda = 5.2 × 10⁻⁶, F_(13,18,394) = 37.57, and P < 0.001, indicating that O–CH₂ wag at 1396 cm⁻¹ can be used as a biomarker of this species group. The species could be categorized into four groups according to phylogenetic similarity, suggesting that the O–CH₂ 1396 cm⁻¹ absorbance is related to the biological traits of each species. This procedure can also be used to complement evolutionary studies.