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This study was carried out to profile key characteristics of intestinal functions and health in wild-caught Ballan wrasse. To describe functional variation along the intestine, samples were collected from four intestinal segments, named from the proximal to the distal segment: IN1, IN2, IN3 and IN4. The sections showed quite similar structure, i.e. regarding mucosal fold height and branching, lamina propria and submucosal width and cellular composition and thickness of the muscle layers. Leucine aminopeptidase and maltase capacity decreased from IN1 to IN4, suggesting a predominant role of IN1 in digestion. Gene expression levels of vitamin C transporter (slc23a1) and fatty acid transporters (cd36 and fabp2) were higher in IN1 than in IN4, indicating a more important role of the proximal intestine regarding transport of vitamins and fatty acids. Higher expression of the gene coding for IgM heavy chain constant region (ighm) was found in IN4 than in IN1, suggesting an important immune function of the distal intestine. Other immune related genes il1b, il6, cd40, showed similar expression in the proximal and the distal part of the intestine. Parasite infection, especially the myxozoan parasite Enteromyxum leei, coincided with infiltration of lymphocytic and eosinophilic granular cells in the submucosa and lamina propria. The present study established reference information necessary for interpretation of results of studies of intestinal functions and health in cultured Ballan wrasse., (Copyright © 2021 Elsevier Inc. All rights reserved.)

Elevated levels of polycyclic aromatic hydrocarbons (PAHs) are detected in aquafeeds where fish oils are (partially) replaced by vegetable oils. The highly lipophilic PAHs solubilize readily in oil droplets and micelles in the intestinal lumen that can affect enzymatic lipid digestion by altering lipase activity. We therefore investigated the effect of two PAHs, benzo[a]pyrene (BaP) and phenanthrene (PHE), on bile salt-activated lipase (BAL) activity in desalted luminal extracts of the proximal intestine of rainbow trout (Oncorhynchus mykiss) using the triacylglycerides rapeseed oil and fish oil as substrates. The hydrolysis of rapeseed oil and fish oil measured at a calculated substrate concentration of 2.2mM, increased linearly up to 30min at 15°C. Substrate dependency under initial velocity conditions was described by simple Michaelis-Menten kinetics with a K m value of 1.2mM for rapeseed and fish oil. Rapeseed oil hydrolysis was inhibited by 1nM BaP and 10nM PHE. The hydrolysis of fish oil was only inhibited by 10μM BaP. The in vitro lipase activity data were corroborated by TLC/HPLC analysis of the reaction products, showing that in the presence of BaP and PHE, 46-80% less free fatty acids (FFA) were hydrolysed from rapeseed and fish oil triacylglycerides. The presence of low concentrations of BaP and PHE decreased rapeseed oil hydrolysis by BAL whereas fish oil hydrolysis was not affected. The replacement of fish oil by rapeseed oil in aquafeeds introduces PAHs that could affect lipid digestion., (Copyright © 2017 Elsevier Inc. All rights reserved.)

The major neutral lipase excreted by the pancreas in fish, is bile activated lipase (BAL). Here we present evidence that cod have a functional BAL and a non-functional pancreatic lipase related protein (PLRP). The Atlantic cod genome does not seem to contain colipase which is essential for pancreatic lipase activity. During the larval stages, the gene expression of BAL was low until the point when pyloric caeca started to differentiate and develop (approximately 20mm standard length (SL)). Then the expression increased until approximately 50mm SL. The PLRP gene was expressed but showed very little regulation. The activity of neutral lipase did not increase in parallel to gene expression. The mismatch between activity and gene expression measurements may be partly explained by the unspecific analytical method, when analysing lipase activity in larva whole body. There is neutral lipase activity in numerous tissues in the fish larvae and the lipase activity in the gut, relatively to activity in the whole body, decreased with age. Furthermore, neutral lipase activity in rotifers was ten times higher than in whole cod larvae with full guts. Activity originating from the live prey may therefore explain the high whole body lipase activity from 3 to 20dph. The results also indicate that "adult type" digestion of neutral lipid develops late in the larval period (from 20mm SL), while other mechanisms of lipid uptake are active at the early larval stage., (Copyright 2010 Elsevier Inc. All rights reserved.)