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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.

A 10‐wk feeding trial was conducted in the laboratory during which channel catfish Ictalurus punctatus (average initial weight: 6.5 g/fish) were fed five practical diets containing either 0, 500, 1,000, 2,000, or 4,000 units of microbial phytase/kg diet. Fish fed diets containing 500 or more units of microbial phytase/kg consumed more feed and gained more weight than fish fed the basal diet without supplemental phytase. Feed conversion ratios (FCR) did not differ among treatments except the FCR for fish fed 1,000 units of microbial phytase/kg diet was lower than that of fish fed no supplemental phytase. Fish survival was not different among treatments. Contrast analysis showed that weight gain, feed consumption, bone ash, and bone phosphorus were higher and feed conversion ratio was lower for fish fed diets supplemented with phytase as compared to fish fed no supplemental phytase. The concentration of fecal phosphorus decreased linearly as phytase supplementation increased. Results from this study demonstrate that microbial phytase is effective in improving bioavailability of phytate phosphorus to channel catfish, which may eventually lead to a reduction in the amount of supplemental phosphorus added to commercial channel catfish feeds.

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