How often do fishes "run on empty"?
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We used a large data set of African, Neotropical, and North American fishes to examine the frequency with which fishes have empty stomachs (nspecies = 254; nindividuals = 36875). Mean percentage of empty stomachs was low across all fishes (16.2 1.2%) but varied from 0% to 79.4% among individual species. Nocturnal fishes had empty stomachs more frequently than diurnal fishes. Trophic classification was strongly associated with the percentage of empty stomachs, a pattern also revealed from an intraspecific analysis. Fishes appear to adjust their feeding intervals relative to the energy density, conversion efficiency, and particle size of their food. Piscivorous fishes seem to be the only trophic group that regularly experience long periods of empty stomachs, with species that consume prey whole and those that provide extended parental care having the highest proportions of empty stomachs. Activity patterns and life histories of some piscivorous species probably have evolved in partial response to energetic benefits of large, energy-rich food resources.