Bacterial Populations in the Gut of the Silver Carp (<i>Hypophthalmichthys molitrix</i>)

Abstract

Abstract Young silver carp (Hypophthalmichthys molitrix) were allowed to feed alternately on manure-silt (M–S) and algal (A) food sources for 1-h periods to determine the retention times and digestibility of those foods and the numbers and types of bacteria in them as they passed through the gut. Food was retained in the gut for 4–5 h at 28.5°C. Feeding rates were similar for M–S and A, but the fish assimilated an average 52.4% of the organic matter in M-S and only 25.6% of the A mixture. The most common aerobic bacterium in the gut was Aeromonas hydrophila. Significant increases in numbers of bacteria occurred from foregut to midgut of fish eating both M–S and A foods, followed by significant decreases in numbers in the hindgut (analysis of variance; P < 0.05); this finding suggests that bacterial populations may increase and then be digested, thereby providing high-quality protein for silver carp. Because fish fed on relatively low-quality agricultural wastes (e.g., swine manure) may grow at rates similar to those of fish fed commercial rations, these data may have valuable implications for feeding and management practices in aquaculture ponds.