Feed intake, growth, feed conversion, digestibility, enzyme activities and intestinal structure in Atlantic salmon (Salmo salar L.) fed graded levels of phytic acid

Duplicate groups of Atlantic salmon (36.4 +/- 0.1 g) were fed graded levels of phytic acid (IP6) for 80 days. The basal diet, to which different levels of sodium phytate were added to obtain 0, 1.0, 2.1, 4.7, 10.0 and 20.7 g IP6 kg(-1) contained fish meal, fish oil and wheat starch. The dose-response relationships between IP6 and feed intake, growth, feed conversion ratio, nutrient digestibilities and nutrient retentions were investigated. Trypsin activities, mucosal enzyme activities, bile acid concentrations and histopathological responses of the distal intestine were studied in fish fed diets with 0, 4.7 and 20.7 g IP6 kg(-1). Feed intake and growth responded negatively and dose dependent to dietary inclusion of IP6. The tolerance level of IP6 with regard to growth and feed intake was between 4.7 and 10.0 g kg(-1). No distinct dose-response relationship was seen for digestibility of nitrogen (N), lipid, and starch, whereas the digestibility of zinc (Zn) and magnesiunt (Mg) was reduced as the inclusion of IP6 increased. Whole-body retention of phosphorus (P) and Mg and lipid accretion decreased with increasing supplementation of IP6, while Zn retention increased, especially for the highest levels of IP6. Fish fed 20.7 g IP6 kg(-1) absorbed 14.6% of dietary TP6, rationalized by a tendency towards increased activities of mucosal alkaline and acidic phosphatase. The activities in tissue of mucosal enzymes such as leucine aminopeptidase and maltase did not correspond closely to the digestibilities of N and starch. The cumulative trypsin activity in intestinal chyme and the bile acid concentration in the pyloric intestine was significantly lowered in the fish fed 20.7 g IP6 kg(-1) compared to the control group. In fish fed diets with 4.7 g IP6 kg(-1) enzyme activities and bile acid concentrations along the gastrointestinal tract were similar to that of fish fed an unsupplemented diet. Inclusion of IP6 did not cause detectable morphological changes in the distal intestine. (c) 2006 Published by Elsevier B.V.