(1) Zooplankton, containing 80% of their lipid as wax esters, were fed to young rainbow trout for up to 3 months without any obvious ill-effects. Although these fish absorbed 90% of the dietary lipid, triacylglycerols were by far the major lipid present in the tissue of the pyloric caeca. Freshwater rainbow trout, which do not encounter large quantities of wax esters in their natural diet, assimilated wax esters as efficiently as herring, a seawater species that has a natural diet of wax ester-rich zooplankton. The efficiency of wax ester absorption did not change over 9 weeks of feeding the wax ester-rich diet. It appears, therefore, that the ability to assimilate these lipids is inherent and widespread among fishes. (2) Electron microscopy showed that the general morphology of the pyloric caeca of rainbow trout fed wax esters and the visible steps of lipid absorption resemble those documented for the mammalian small intestine and its absorption of triacylglycerols. The distribution of lipid in the pyloric caeca supports the hypothesis that this tissue is involved in lipid absorption and metabolism in fish fed wax esters. The trout could digest and absorb the zooplankton lipid within 18h, which is consistent with their being capable of deriving much of their carbon from dietary wax esters. (3) Hexadecanol, glucose and aspartate were all incorporated into tissue triacylglycerols and there was evidence for a link between hexadecanol oxidation and glycerol phosphate synthesis. The rates of triacylglycerol formation from the water-soluble and the hydrophobic substrates were similar. The water-soluble substrates (except glycerol) had a higher rate of CO2 production. There was no clear-cut effect of species or diet on the rate of substrate metabolism. (4) There was no evidence of fatty acid- or fatty alcohol-binding proteins in fish analogous to the fatty acid-binding protein of rat. The 'binding' of fatty alcohol, and to a lesser extent fatty acid, to high molecular constituent(s) of liver and caecal cytosols may be due largely to non-specific interactions with lipid. (5) A soluble NAD+-dependent ethanol dehydrogenase purified from trout caeca did not readily oxidize hexadecanol, in contrast to the crude cytosolic fraction. The greatest rate of hexadecanol oxidation in the pyloric caeca and liver of trout was achieved by an NAD+-dependent microsomal system. The microsomal fraction also contained an NAD+- dependent acetaldehyde dehydrogenase which may be involved in the further oxidation of aldehyde to acid. Feeding fish wax ester-rich zooplankton had no obvious effect on the activity of these enzyme systems. (6) The metabolic activity of the tissue slices and subcellular fractions were much less than the capacity of the intact fish to dispose of dietary wax ester. There are several possible reasons for this discrepancy, including the problems of studying enzyme catalysis in heterogeneous systems.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:449224 |
| Date | January 1978 |
| Creators | Bauermeister, Anne E. M. |
| Publisher | University of Aberdeen |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://digitool.abdn.ac.uk/R?func=search-advanced-go&find_code1=WSN&request1=AAIU446299 |
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