Effect of water temperature and diet on cell membrane fluidity and fatty acid composition of muscle, liver, gill and intestine mucosa of adult and juvenile steelhead trout, Oncorhynchus mykiss

Wijekoon, Manjusri Pandula Atapattu (2012) Effect of water temperature and diet on cell membrane fluidity and fatty acid composition of muscle, liver, gill and intestine mucosa of adult and juvenile steelhead trout, Oncorhynchus mykiss. Doctoral (PhD) thesis, Memorial University of Newfoundland.

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Abstract

Chapter I highlights the significant role of lipids in fish as a source of metabolic energy for growth, reproduction, movement and health. Dietary lipids also influence the fatty acid composition in various tissues including cellular membranes altering composition and function. Fish oil (FO) derived from capture fisheries is the main source of lipid in aquaculture feed to provide the essential fatty acids for maricultured fish. However, limitations in FO availability have prompted the investigation of the use of vegetable oil and animal fat as substitutes for fish oil and are investigated in this study. -- Chapter 2 reports the results of investigation of the effect of FO substituted commercial and experimental diets on muscle lipid class and fatty acid composition in adult and juvenile steelhead trout (Oncorhynchus mykiss). Study (i) compared herring oil (HE) diets with those containing medium levels of omega 3 fatty acids (M-ω3) and lower ω3 levels (L-ω3), and study (ii) compared HE with sunflower oil (SF) and flax seed oil (FLX). The results of both studies indicate the possibility of substitution of FO without compromising growth, feed efficiency or health once the minimal essential fatty acid requirements are met in the diet. HE diets with higher ω3 levels (H-ω3) in both studies significantly increased the ω3 highly unsaturated fatty acid composition in muscle tissue with a corresponding decrease in plant terrestrial fatty acid composition (p ≤ 0.045). However, fish fed M-ω3, L-ω3, SF and FLX diets selectively accumulated DHA (docosahexaenoic acid) in muscle tissue minimizing the dietary differences in both adult and juvenile fish. All M-ω3, L-ω3 and SF diets were rich in linoleic acid and increased the ω6 composition in muscle tissue altering the ω6:ω3 ratio. In contrast, both HE and FLX diets had similar ∑ω3 and ω6:ω3 ratios due to the high availability of linolenic acid in FLX feed. Triacylglycerols were the main neutral lipid stored in muscle tissue (above 80 - 90% total lipid). Changes in water temperature had minimal effects on muscle lipid composition in both adult and juvenile fish. -- Chapter 3 investigated the effect of H-ω3, M-ω3 and L-ω3 diets and changes in water temperature on liver membrane fluidity, lipid class and fatty acid composition in adult fish. Fish were sampled from the initial (l3.5°C), middle (18.0°C) and final (13.5°C) experimental temperatures used in study (i). The membrane fluidity was determined by measuring the CH₂ symmetric stretching bands in Raman spectroscopy at 2850 cm⁻¹. The stretching frequencies were obtained by subjecting the liver lipid to a temperature range of 2 to 30°C in increments of 4°C. The physical properties of the liver membrane lipid in fish fed H-ω3 diets was the least influenced by quickly adapting to either an increase or decrease in water temperature. The membrane fluidity of fish fed M-ω3 diets at 18.0°C, was similar to fish fed H-ω3. The liver membranes of L-ω3 diet fed fish sampled at both 18.0 and 13.5°C became increasingly more fluid than both H-ω3 and M-ω3 fed fish during the Raman trial. The fatty acid proportion of 20:3ω6 and 20:4ω6 at 18.0°C and 20:3ω6 at 13.5°C (final) was significantly higher in fish fed L-ω3 diets and may have influenced the increased fluidity in liver cell membranes. Both M-ω3 and H-ω3 fed fish have the capability to withstand a broader temperature range without undergoing complete phase separation of membrane lipids. -- Chapter 4 evaluated the lipid composition of gills, intestine mucosa and liver tissue of juvenile steelhead trout using HE, SF and FLX diets, during a water temperature increase from 8 to 18.0°C. The lipid class composition of gill tissue was not affected by diet or temperature. Both SF and FLX diets significantly increased the terrestrial fatty acid composition and ω6:ω3 ratio in gills of juvenile steelhead trout. The variation in diets also influenced the storage and selection of fatty acid substrates for β-oxidation in juvenile steelhead trout. Fish fed HE diets deposited a higher amount of saturated fatty acids in the liver while monounsaturated fatty acids were significantly higher in both SF and FLX diet fed fish. Both SF and FLX diets stimulated chain elongation and desaturation in steelhead juveniles. The SF diet stimulated the production of arachidonic acid while eicosapentaenoic acid production was promoted by the FLX diet.

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