Dietary fish oil augments the function and fluidity of the intestinal brush‐border membrane of the carp

Two groups of carps were raised on a commerical nutritionally complete diet: one was the control group, the other was fed the same diet enriched with 7% fish oil. The experiment lasted seven months (July through February), during which time the environmental temperature dropped gradually from 25°C to 13°C. Intestinal microvillus membranes were isolated after four and seven month feeding and examined for fluidity by fluorescence polarization with 1,6‐diphenyl‐1,3,5‐hexatriene. The functionality of the membrane was assessed by the activity of the intrinsic enzyme alkaline phosphatase. The experimental group exhibited increased membrane fluidity and elevated enzyme activity only when the environmental temperature decreased to 13°C. These changes in the membrane properties seemed to correlate with alterations in the fatty acid profile of the membrane phospholipids. Whereas the control group showed some increase in the n−3 C20∶5, C22∶5, and C22∶6 fatty acids most likely due to cold adaptation, the membranes isolated from the group fed fish oil showed a considerably higher level of these fatty acids reflecting the combined effect of the dietary manipulation and cold adaptation.