Gut evacuation and absorption efficiency of walleye larvae

Gut evacuation and absorption efficiency in zooplanktivorous walleye Stizostedion vitreum larvae (10–19 mm; 0.53–6.8 mg dry weight) were examined in the laboratory. The decline in dry weight of whole digestive tract contents was examined at 15, 20, and 25) C in discontinuous feeding larvae. The observed relationship between short-term evacuation rate and gut fullness indicated that evacuation approximated most closely an exponential decline. When gut evacuation rate, R , was calculated as the slope of loge gut fullness v . time there were significant effects of temperature and walleye size on R . Gut evacuation rate was higher at 20° C than at 15 or 25° C and declined with increasing walleye dry weight. Absorption efficiency at 20° C was examined by qualitative analysis of food and faeces. Apparent digestibility, D _a, of crustacean zooplankton increased with gut retention time and declined with walleye dry weight. Maximum D _a was estimated to be 79% of organic matter from food retained in the gut for 6 h.