The aim of this study was to analyse the digestibility and viability of diatoms following gut passage through Aegla uruguayana. Crabs (n=28) and diatom samples were collected from Las Pencas Stream (Entre Ríos Province, Argentina). Organisms were allowed to graze on the source, then they were placed in aquaria to defecate. Samples of faecal and source material were analysed microscopically to quantify 'live', 'dying' and 'dead' diatoms, and inoculated onto Chu 10-infused agar cultures to observe cell viability. Significant differences were found among source and faeces content of 'live' and 'dead' cells (p<0.01). Nevertheless, the percentage of digestion after gut passage was only 11.5 %. Both agar cultures produced colonies that increased in cell density over time with significantly higher enhancement in faecal treatment (p<0.05). Evidence of digestion resistance and reproductive stimulation by gut passage could be tested in this experience.