The apparent dry matter digestibility (ADMD), apparent protein digestibility (APD), and apparent amino acid digestibility (AAAD) of thirteen feedstuffs used for marine shrimp diets were determined for the marine shrimp, Penaeus vannamei. The feedstuffs evaluated were casein, corn starch, gelatin, soy protein, wheat gluten, fish meal, rice bran, shrimp meal, soybean meal, squid meal, cellulose, chitin, and diatomaceous sand. Each feedstuff comprised 88% of the experimental diets. The ADMD values ranged from 91.4% to -21.4%.The purified feedstuffs were more efficiently digested than the practical feedstuffs. The dietary fillers (cellulose, chitin, and diato maceous sand) were either poorly digested or not digested.The APD values ranged from 99.1% to 3.0%. There were no differences in APD due to animal or plant feedstuff origin. The AAAD were determined for arginine, lysine, leucine, iso leucine, threonine, valine, histidine, phenylalanine, glutamate, aspartate, glycine, proline, serine, tryrosine, and alanine. The digestibility trends observed for APD were similar for AAAD. The high AAAD for chitin suggested that the low APD was due to the low digestibility of the amine fraction of the chitin structure and not a low protein digestibility. Arginine, lysine, and glutamate were most efficiently digested, while alanine had the lowest apparent digestibility value.

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Adult red swamp crayfish (Procambarus clarkii) were held in fecal collection chambers and fed common feedstuffs isosubstituted in experimental diets. Apparent dry matter digestibility (ADMD) and apparent crude protein digestibility (ACPD) coefficients were determined by the total collection and indicator (chromic oxide) methods. Feedstuffs tested were menhaden fish meal, soybean meal, alpha‐soy protein, casein, gelatin, wheat bran, rice bran, wheat gluten, shrimp meal, crab chitin, cellulose, squid meal, corn starch and diatomaceous sand. Rate of consumption of plant feedstuffs was generally higher than feedstuffs of animal origin. Consumption of fish meal and shrimp meal was low (0.59 and 0.44% body weightlday, respectively). Fecal chromium concentrations were lower than chromium concentrations of experimental diets and precluded calculation of realistic coefficients by the indicator method. Analysis of refused feed samples indicated that crayfish did not consume the indicator in the same proportion as the remainder of the diet; therefore, the total collection method was judged the better approach to determining digestion coefficients. ADMD and ACPD coefficients of plant feedstuffs were generally higher than coefficients determined for animal feedstuffs. ADMD coefficients indicated substantial carbohydrate digestion by crayfish.