Comparison of diatom community structure from epilithon and fish guts: implications for inferring past changes in water quality

The sampling skills of three common European fish species (Barbus barbus, Chondrostoma nasus and Squalius cephalus) were tested to assess their potential as biomonitors of past changes in river water quality through the analysis of diatoms in fish guts. The study was performed on three rivers with different chemical and physical conditions. Comparison of similarity indices revealed low diatom assemblage resemblance between epilithic samples and samples collected from fish guts at the same locality. In contrast, a mixed-effect linear model identified significant differences between locations through comparison of diatom-based water quality indices. Among fish species, diatom indices calculated from gut samples of B. barbus and C. nasus were in most cases not significantly different from those from epilithic samples while those from S. cephalus were often significantly different. The results of the study demonstrate that diatom analysis of fish guts provides a clear distinction between eutrophic and hypereutrophic rivers. Finer nutrient variations within hypereutrophic conditions were also found to be significant for some diatom indices. In this context, choice of appropriate diatom water quality index proved to be crucial in maximizing the sensitivity of the method.