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% and 75% of their initial P respectively. This suggests that previous egestion research that does not measure leaching underestimates fecal nutrient content. Foregut-hindgut analyses are unaffected by leaching and so effectively complemented incubations. These analyses provided enough hindgut material to estimate fecal %P and allowed us to estimate both dietary nutrient intake (when unknown) and the relative quantity of P in the diet and in the feces. Overall, we suggest that future researchers combine incubations and foregut-hindgut analyses to estimate aquatic animal waste production.

These data are measurements of P egestion/excretion, foregut-hindgut %P, and fecal %P leaching in threespine stickleback. Collection sites were: Sooke River (British Columbia) and Miami Creek (British Columbia).  We performed experiments at low temperatures (16 ± 2 ˚C) and at high temperatures (22 ± 1.5 ˚C). 

1. We incubated stickleback in 2L of water for 24h and measured their P excretion and egestion. This dataset shows how much P they excreted, how much they egested, and data on their gut clearance and morphology/stoichiometry. It also shows how much individual fish consumed immediately prior to experiments. All stickleback are from Sooke River in British Columbia. 

2. We collected stickleback from Sooke River and Miami Creek and dissected out their guts. We removed material from the stomach and hindgut (last 10mm) and took its P content. We also did this on a subset of fish from the experiment described in (1) that did not clear their guts. 

3. We collected hindgut contents from individuals that did not clear their guts in experiment (1) and from field-caught fish. We incubated this feces in water for indicated periods of time and recorded the difference in %P before and after this incubation to quantify fecal P leaching.