Microscopy in combination with image analysis for characterization of fishmeal material in aquafeed

The aim of this study was to investigate the use of microscopy in combination with image analysis (IA) measurements for the characterization of fish bone lacunae in aquafeed-extracted material. For this purpose two experiments have been conducted. In experiment (exp.) 1, six samples of fish meal based aquafeed were analyzed by the microscopic method, according to Annex VI of Regulation 152/2009. Sediment fractions of each sample were observed with a compound microscope at ×40. Two hundred and fifty eight bone fragment lacunae images were recorded and processed through IA software. Accordingly, on each lacuna 30 geometric variables have been obtained and measured. The geometric variables have been grouped in two main families, namely size descriptors and derived shape descriptors. In exp. 2 measurements obtained from 1081 bone lacunae (644 for mammals and 437 for poultry) acquired from 14 mammalian and 7 poultry samples have been merged with the aquafeed dataset (258 bone lacunae). Results obtained in exp. 1 indicated that nearly two thirds of the descriptors presented differences among the analyzed samples. Differences in observed values were not systematically distributed among the six samples. Nevertheless, in all analyzed samples features of lacunae have shown an overlap. By contrast the comparison of fish bone lacunae with avian and mammalian bone lacunae (exp. 2), has revealed a large gap between terrestrial and aquatic animals in the case of several descriptors (16 primary and 8 secondary descriptors). Therefore, it can be concluded that combining light microscopy and image analysis: (i) fish material in aquafeed appears quite homogenous in term of bone features; (ii) fish material can be distinguished from avian and mammalian materials by selecting specific descriptors.