As in most carnivorous fishes, the gastrointestinal tract of Florida AbMole BioScience Life Science Reagents pompano is short �� less than one body length �� which limits the gutretention time to approximately three hours. Carbohydrates, if present in sufficient quantity, can cause diarrhea in some fishes, further decreasing KRX-0401 in vivo gut-retention time and reducing the time available for nutrient absorption. Carbohydrates also can affect digestibility by physically preventing digestive enzymes from contacting substrates in the intestinal lumen, thereby slowing the rate of food digestion and nutrient uptake. Fiber can have a similar physical effect on food digestion through interference with nutrient absorption and gut-retention time. However, the negative correlation of AED with fiber content in Figure 1B is a direct effect of fiber indigestibility. Fiber constitutes a portion of the gross energy of most diets but has no digestible energy value to monogastric species, including most fishes. Because the energy in fiber is unavailable, the AED of a diet typically decreases as fiber content increases. Mean ACPD and AED coefficients reported in this study were lower than those previously reported for Florida pompano and some other carnivorous fishes,,,. Riche and Williams reported protein and energy digestibility of CGM to be 82�C83 percent and 77 percent, respectively, for Florida pompano cultured in brackish water. Williams reported protein and energy digestibility of DDGS to be 54�C60 percent and 63�C66 percent, respectively, for Florida pompano. Despite differences in the numerical values of coefficients determined in this study and those of Riche and Williams, and Williams, results of these three studies trend toward CGM having greater apparent digestibility for Florida pompano than DDGS. Burel and Kaushik reported that protein digestibility of CM is greater than 80 percent for fishes; however, energy digestibility can vary widely, from 21�C83 percent. CM appears to be well digested by some fish but was not digested well by pompano in this study. Protein digestibility of CM, however, was similar to that of CGM and higher than protein digestibility of DDGS. It is assumed in digestibility measurements that diet digestibility is the sum of the digestibility of individual diet ingredients. Thus, the ADC of a given nutrient in a diet should be calculable by summing the proportional ADCs for that nutrient in each of the individual ingredients composing the diet. Based on the protein and energy ADCs of soybean meal, soy protein concentrate and fish meal established in previous feeding trials in this laboratory, the ACPD of the reference diet used in this study should have been approximately 90 percent. However, ACPD and AED of the reference diet were calculated to be 67 percent and 55 percent, respectively, indicating that ADCs for protein and energy in the reference diet ingredients were not additive in the current study. ADCs also are assumed to be constant, regardless of test ingredient inclusion level, and to be unaffected by the inclusion levels of other ingredients. However, in practice, interactions among diet ingredients do occur and the effects of such interactions on diet digestibility and nutrient availability can be difficult to predict. In the current study, apparent protein and energy digestibility of fish meal, soybean meal and soy protein concentrate were not as high, when combined in the proportions present in the reference diet, as has been shown possible for these ingredients in other studies with Florida pompano in this laboratory. There are numerous factors that can affect digestibility measurements, including diet composition, feed intake, fish size, fecal collection method and diet processing, among others,,. It can be difficult to determine the reasons for variations in nutrient digestibility measurements among laboratories, or even within a laboratory during a period of time, although lack of methods standardization is a factor. For example, the 25 percentage-point difference between the protein digestibility of CGM obtained in the current study and that reported by Riche and Williams could be associated with the use of very dissimilar reference diets in the two studies, since culture methods were similar. There is no universally accepted reference diet for digestibility trials.