Gastric evacuation of formulated feeds in brook trout

Abstract

Gastric evacuation rate (GER) can be used to estimate stomach fullness in fish at any postprandial time, to predict return of appetite and optimize feeding regimes. The influences of meal size, fish size L (cm), temperature T (°C), dietary energy density E (kJ g–1) and feed storage conditions (frozen, ambient conditions), on GER of brook trout fed a single meal of commercial pellets were studied. In addition, the effect of a second meal on GER was examined. Small (15 cm) and large (23 cm) fish were fed three meal sizes (close to satiation, 50% and 25%). GE was analyzed using a general power function, and data indicated that the square root function best described GE in brook trout independently of meal size. GER experiments performed at 12.5° C, 13.2° C, 15° C, 16.8° C, 18.6° C and 20° C revealed an exponential increased in GER from 12.5° to 18.6° C and then a sharp decline at 20° C. The effect of dietary energy density was determined using meals of 12.6 kJ g–1, 17.7 kJ g–1, and 22 kJ g–1. GER increased with decreasing energy density of the meal. Neither feed storage conditions nor the arrival of a second meal influenced GER. The GER model for brook trout fed commercial pellets was 〖dS〗_t/dt= -0.000860L^1.31 〖E^(-0.41) e〗^(0.08 T) (1-e^1.82(T-20.6 ) )√(S_t ) (g h-1), where St is current stomach mass (g) and t is time (h). This GER model was used to calculate the amount of food that should be present in the stomach of a brook trout that had been fed on three consecutive days. The predicted values were similar to the observed (r2 = 0.987). The GER model can be used to predict stomach content in fish that have been fed repeatedly and should have applications in the development of feeding routines for brook trout.