Measuring egestion, excretion, fecal leaching, and foregut-hindgut %P in threespine stickleback

Most aquatic research on animal waste production evaluates excretion and not egestion, as it is difficult both to collect feces and to accurately analyze its nutrient content. This limits our understanding of how individuals process their dietary nutrients and how animal waste production impacts ecosystems. In this study, we systematically analyzed whether incubation experiments effectively quantify egestion (at high and low temperatures), estimated fecal phosphorus (P) leaching, and evaluated foregut-hindgut analyses as a complementary method. Incubations were superficially effective but were flawed. Although 82% of fish in high temperature incubations and 75% of fish in low temperature incubations egested in 24h, a minority of fish cleared their guts (38% at high temperatures and 6% at low temperatures), making analyzing full nutrient input and output impossible. Furthermore, feces leached P rapidly and variably; a field population’s and an experimental population’s feces leached 41% ...