Prebiotics Have Limited Effects on Nutrient Digestibility of a Diet Based on Fish Meal and Soybean Meal in Goldfish

Abstract

This study evaluated four prebiotics: GroBiotic-A (a mixture of partially autolyzed brewers yeast, dairy ingredient components and dried fermentation products), mannanoligosaccharide (MOS), galactooligosaccharide (GOS), and the fructooligosaccharide (FOS) inulin on digestibility of diets based on fish meal and soybean meal by goldfish Carassius auratus. A basal diet was formulated with 50% of the protein provided by dehulled, solvent-extracted, soybean meal and the other 50% by menhaden Brevoortia sp. fish meal. Each prebiotic was supplemented to the basal diet at 1% by weight. A diet containing all of its protein from menhaden fish meal also was prepared as a control diet. Chromic oxide was added to the diets at 1% by weight. Each diet was fed to adult goldfish in duplicate 110-L aquaria for 8 weeks. The dried fecal material from each aquarium was pooled over time and analyzed for protein, lipid, organic matter, and chromium in order to compute coefficients of apparent digestibility. Genomic DNA of luminal gut microbiota also was isolated from the fecal samples of goldfish fed the various diets and was subjected to PCR using bacteria-specific PCR primers. Then, denaturing gradient gel electrophoresis (DGGE) of the resulting amplicons was conducted as a means of assessing diversity of microbiota in the gastrointestinal (GI) tract. Results revealed that none of the prebiotics affected apparent digestibility coefficients of the diet based on fish meal and soybean meal compared with the basal diet, although the diet supplemented with MOS consistently yielded the lowest values. In addition, goldfish digested the fish-meal–soybean-meal-based diets as well as the control diet. No differences in microbiota of goldfish fed the various prebiotics were revealed by DGGE. These results are in contrast to those obtained with carnivorous fish species such as the red drum Sciaenops ocellatus in which the prebiotics increased digestibility coefficients of diets based on fish meal and soybean meal and altered GI tract microbiota.

Received July 19, 2011; accepted December 21, 2011