General empirical models for predicting the release of nutrients by fish, with a comparison between detritivores and non‐detritivores

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Summary1. We derived models of nutrient release [nitrogen (N) and phosphorus (P)] by fish based on studies that directly measured the release rates from 56 species across a broad range of fish mass, feeding histories and temperature.2. We developed four separate models of nutrient release from multiple regression analysis: detritivore release rates of N and P, and non‐detritivore release rates of N and P.3. Fish mass explained most of the variance (78–92%) in release rates.4. Our predicted rates of release of P by fish (g ha−1 day−1) were similar to observed rates in the literature from other lakes.5. The influence of a shift in diet (planktivory to detritivory) by a single species (gizzard shad, Dorosoma cepedianum, a facultative detritivore) on nutrient release rates was estimated. During periods of detritivory, gizzard shad accounted for on average 39% (<1–96%) of all nutrients released by the fish assemblage, and increased total fish assemblage release rates on average by 59% (<1–331%) compared to when gizzard shad were modelled as planktivores.6. These models provide a rapid means for predicting the release of nutrients by fish assemblages and may facilitate more comprehensive comparisons of nutrient cycling by fish with other internal pathways.