Effect of temperature on the gastric evacuation in sprat Sprattus sprattus

Gastric evacuation of groups of juvenile (mean 63 mm total length, LT, 0.283 g dry mass, MD) sprat Sprattus sprattus feeding on brine shrimp Artemia sp. nauplii was studied at six temperatures (7.5, 10, 13, 16, 19.5 and 21.5 degrees C) in the laboratory. Gastric evacuation was best described with a general model: St=S0(1-B)-R(1-B)t)1-B(-1), with St=stomach content at time t, S0=stomach content at time 0, t=time , R, B=constants. The shape parameter was estimated as B=0.668. For comparison with other studies, an exponential model was fitted also to the data. The evacuation constant (R) of the general gastric evacuation model increased exponentially with temperature between 7.5 and 16 degrees C. The slope of the increase was reduced between 16 and 19.5 degrees C and a slight decrease was observed between 19 and 21.5 degrees C. Additionally, the effect of mean MD (range 0.286-1.025 g) was examined. A simple power function (R=R'MDC) described the influence of predator mass on exponential evacuation constant with C=0.503. The results of this investigation were integrated into a consumption model for the calculation of daily rations of S. sprattus: C24=0.0177e0.0775T/S0.668 MD0.503 (1-{1[1+e(-0.659)(T-23.989)](-1)})24/S0.668, with T=ambient temperature (degrees C) and /S0.668= mean of field stomach contents (g dry) individually raised to the power of 0.668.