Pre-hydrolysis improves absorption of neutral lipids in Atlantic halibut (Hippoglossus hippoglossus, L.) larvae

To investigate if digestion is limiting for absorption of dietary neutral lipids in Atlantic halibut (Hippoglossus hippoglossus, L.) larvae, absorption of triacylglycerol (TAG), diacylglycerol, (DAG), and monoacylglycerol, (MAG) as well as phosphatidylcholine (PC) was studied by tube-feeding larvae with radio-labelled lipids and tracing the radioactivity. PC was included to evaluate any difference in absorption of neutral versus polar lipids. The labelled lipids where deposited by tube-feeding before larvae were incubated individually for 18 h with collection of expired CO2. At sampling, the gut was separated from the body carcass and radioactivity traced in four different compartments, namely body carcass, gut, incubation water and CO2 expired from larvae. The relative (%) isotope distribution of each compartment was calculated and the dose size effect analysed by regression analysis.The results show that there is an increasing amount of evacuated unabsorbed neutral lipids as the complexity of the lipid increases (TAG > DAG > MAG). The larval faecal evacuation ranged from 66 ± 20% of TAG to 9 ± 6% of MAG. DAG was intermediate with 52 ± 21% evacuated. Of the labelled PC, 37 ± 16% was absorbed, but this can not be directly compared to the neutral lipids due to the different digestive enzymes that specifically hydrolyse neutral and polar lipids. Increasing the administered amount of lipids only slightly increased the total amount of labelled TAG and DAG that were actually absorbed, while there was a linear correlation between fed and absorbed MAG. The absorption of PC was also linearly related to the administered amount. The difference in net absorption of labelled TAG, DAG and MAG diets indicates that digestion is a limiting factor for absorption of neutral lipids in Atlantic halibut larvae.