Discrimination between endogenous and exogenous water sources in juvenilerainbow trout fed extruded dry feed

摘要

A tracer (Cr-51-EDTA) study was undertaken with juvenile (20 g) freshwater rainbow trout, Oncorhynchus mykiss, using an experimental design that minimized stress effects during feeding and drinking trials. A calculation procedure was developed, where feed intake (pellet number), tracer intake (mL, water in stomach contents (g) and drinking rate (mL-kg(-1).h(-1)) are essential to discriminate between the major stomach water sources prandially and postprandially: water bound in food; initial water absorption of pellets prandial water intake; postprandial water intake and endogenous stomach secretion. We put forward the hypothesis that intake of dry food with a minor water content (10 %) may impose a demand for water to moisture the feed up to the level in natural feed (75 %) as preparation for gastric emptying, whereafter food is ready to pass from the stomach through the pyloric sphincter. Moisture content of pellets increased from 9.4 to 24.9 % in the pre-meal period. The pellets were ingested with 4.0 to 19.3 muL water per pellet, reflecting high inter-individual variation. Prandially moisture content rose to 52 % and further increased to 56 % in the delay period. Moisture content was ca. 65 %, when pellets began to disintegrate and move through the sphincter in accordance with the hypothesis. Stomach secretion contributed 34-44 % of the stomach water and ingested water 25-35 %, The sampling and calculation procedure gave convincing evidence for the detailed stomach water budget and this individual,approach can be very useful in comparisons of artificial and natural diets.