Methods of Fecal Collection and Nutrient Leaching in Digestibility Studies

Abstract

Quantitative data are presented on nutrient leaching from fish feces remaining in water for varying periods. Rainbow trout (Salmo gairdneri) were fed a multicomponent diet and feces produced were collected from the trough sediment with a fine-mesh net after 1, 4, 8, and 16 h. Removal of fecal samples from the lowest 2.5 cm of the intestine followed by 1 h water immersion gave digestibility coefficients comparable to those of feces netted from trough sediment at 1-h intervals. This relation suggested that absorption of nutrients was completed before the materials moved into the lower 2.5 cm of intestine. Most leaching of nutrients from feces occurred during the first hour in water. Storage of feces in trough water for 1 h increased digestibility estimates for dry matter, protein, and lipid by 11.5, 10.0, and 3.7 percentage points, respectively. A gradual increase in leaching of nutrients continued up to 4 h, but little or no leaching occurred between 4 and 16 h after defecation. In a second experiment, four methods of fecal collection were compared after rainbow trout were fed pelleted herring meal. Collection of the lowermost fecal pellet by intestinal dissection or anal suction gave equivalent digestibility coefficient values for dry matter, crude protein, and crude lipid. Netting of fecal sediment up to 1 h after defecation gave values for dry matter and protein that were elevated by about 5%, whereas samples collected by the stripping technique gave values 5% lower than those for samples collected by intestinal dissection and anal suction.