Fish intestine plays various physiological functions and its integrity is essential to guarantee fish growth and
welfare. Several laboratory techniques have been proposed for studying morpho-physiology of fish intestine, but
classical histology still represents one of the gold standards. Nevertheless, this technique is time consuming and
does not provide comprehensive information on the biochemical composition of tissues. The present study,
introduces a new approach for studying fish intestine, the Fourier Transform Infrared (FTIR) spectroscopy. This
is a fast, label-free analytical technique, which analyses the vibrational transitions induced on tissues by the
interaction with the electromagnetic radiation. On the base of vibrational features of some functional groups
classes and molecular bonds, FTIR allows the analysis of the macromolecular composition of the sample.
Rainbow trout (O. mykiss) represents an important species for modern aquaculture and deeper knowledge about
its intestine anatomy and macromolecular composition is desirable. In the present study, besides the traditional
histological analysis, the biochemical building of the intestine mucosa was analyzed for the first time by FTIR.
Spectral data can be considered a complement to traditional histological analysis.
