The high amount of starch in the LNSP feces, combined with the small particle size, was most likely the main reason for the high short-term degradability of LNSP feces. Approximately 25% of the COD present in the fecal waste was degraded within 1–2 h by the bacteria present in the incubation compared to 8% in the fecal waste deriving from the HNSP diet. Klas et al. (2006) reported a readily degradable COD fraction of 4% in solid waste collected at a fish farm,which corresponds well with the short-term degradability of 8%found in HNSP feces. The short-term degradability of HNSP feces was approximately three times less than LNSP, and substantiates the hypothesis that high NSP contents in feces limit carbon bioavailability. Both experimental diets are outside the common range of ingredients of current commercially produced diets. However, the contrast between the diets (type of carbohydrate) demonstrated that dietary composition can influence COD bioavailability in fecal waste.