J. Horppila, Diel changes in diet composition of an omnivorous cyprinid - a possible source of error in estimating food consumption, HYDROBIOL, 400, 1999, pp. 33-39
Diel changes in diet composition of omnivorous roach (Rutilus rutilus (L.))
and the effects on food consumption estimates given by a bioenergetics mod
el were studied. In all length groups of roach, the percentage of zooplankt
on in the diets was higher and the percentage of zoobenthos, plants and det
ritus lower during daytime than during the night. As a result, compared wit
h sampling throughout the day, consumption of zooplankton was overestimated
(by 6-11%) and the consumption of other food categories underestimated (by
up to 200%) when only daytime samples were taken into account. The error c
aused by the diurnal diet variation was larger than that caused by a 10% de
viation in the digestibility of prey and energy contents of predator and pr
ey. The results suggest that diurnal changes in diet composition may consid
erably bias food consumption estimates for fish species that feed both on a
nimal prey and plant material. Additionally, estimates for fish-mediated nu
trient recycling may be biased by inaccurate determinations of fish diets.