Lipid absorption in different segments of the gastrointestinal tract of Atlantic salmon ( Salmo salar L.)

Abstract

Gastrointestinal lipid absorption in Atlantic salmon was studied following force-feeding with a standard grower diet to which isotope-labelled free fatty acid (FFA) [1- 14C]-decanoic acid ( 14C-10:0) and triacylglycerol (TAG) [9,10- 3H(N)]-triolein (trioleic acid; 3H-18:1) were added. Following force-feeding, the 15 fish, with an average weight of 704 g, were kept in five circular tanks, three fish per tank, supplied with seawater (salinity, 32 g l −1). At 3, 6, 12, 18 and 48 h, the fish from one tank were killed, and the gastrointestinal (GI) tract was removed and divided into six segments: stomach (ST), anterior, mid, and distal pyloric ceca (PCA, PCM, and PCD, respectively), mid intestine (MI), and distal intestine (DI). The levels of radioactivity (dpm [disintegrations per minute] μg −1 tissue) from the 14C-10:0 and the 3H-18:1 substrates were measured in tissue samples from each segment, allowing an estimation of the amounts of fatty acid substrates absorbed from the lumen into the intestinal cells. The highest levels of radioactivity from both fatty acid substrates were measured in tissue from pyloric ceca (PC) 12 to 18 h after force-feeding. The level of radioactivity from the 14C-10:0 substrate was significantly higher in the PCA than in the PCM and PCD, while there was no clear difference in the level of radioactivity from the 3H-18:1 substrate measured among the different PC tissue segments and the level measured in MI. The level of radioactivity in tissue from DI was negligible to low for both fatty acid substrates. Total lipid accumulation in tissue from PCM, MI and DI was quantified morphometrically at each sampling point using light microscopy and image analysis. These results confirmed the findings from the isotope study, where the highest levels of fat were present at 12 and 18 h following force-feeding. In conclusion, PC was the most important site for fatty acid absorption in the GI tract of Atlantic salmon.