Several Marine Aquaculture Fish Lipid Metabolism And Transport Of Fatty Liver Symptoms

Liver lipid over deposition is a serious and usually fatal progressive issue that commonly occurs in the sea-caged, farm-raised large yellow croaker. The aim of the present experiment was to determine the impact of structure and fatty acid profile alterations in the large yellow croaker liver on hepatic lipogenic enzymes and antioxidant enzyme. Sampled in the East China Sea, fish livers were divided into three groups: normal liver, mild lipid deposition liver and lipid over deposition liver, according to gross and histological examination. The liver fatty acid profile and the activities of enzymes were determined respectively.The results indicated, as the hepatic lipid deposition increased, saturated fatty acid and n-3 polyunsaturated fatty acids (PUFA) significantly decreased, but mono-unsaturated fatty acids and n-6 PUFA increased. The ratio of n-3/n-6 is the highest in normal liver, decreased about 4-fold in mild lipid deposition group and 8-fold in lipid over the deposition group.NADPH-generating enzyme, ICDH and 6PGDH were inhibited in the early stage of lipid accumulation, but increased significantly in the latter stage. The liver lipid deposition level had no significantly effect on G6PDH (P > 0.05). As the liver lipid deposition increased, the antioxidant enzyme, SOD and CAT, and also the lipid peroxidation product, malondialdehyde (MDA), significantly increased (P<0.05). Atlantic halibut, cod and haddock are important farmed marine fish in Canada. However, limited information is available on their essential fatty acid requirements and tissue lipid composition. Most marine fish are incapable of synthesizing polyunsaturated fatty acids de novo and these fatty acids must be supplied in the diet. In present studies show that wide variation exists in the ability of these fish to utilize and accumulate dietary lipid in liver, muscle and other tissues. This study was conducted to determine the differences in muscle and liver lipid composition of halibut, haddock and cod to obtain basic information for designing future studies on EFA requirements and effective use of alternative lipid sources to replace marine fish oil in their diets.Three groups of halibut (3704±221 g), haddock (538±83 g) and cod (276±61 g) were maintained on commercial feeds mainly based on fish meal and marine fish oil for 12 weeks prior to sampling. The lipid content of the gadoid (cod and haddock) and halibut diet was 14.7% and 17.6% respectively. The fatty acid composition of muscle and liver was determined by GC/FID after derivitization of extracted lipid into their fatty acid methyl esters (FAME). Lipids were also fractionated into neutral lipid (NL) and polar lipids (PL) using a Waters silica Sep-Pak?. The phospholipid fraction was further separated into PA, PC, PE, PI and PS by HPTLC and the FAME profile obtained.Cod and haddock are lean fish and their total muscle lipid content was 0.8 and 0.7%, respectively, and PL constituted 83.6 and 87.5% of this lipid. Total liver lipid content of cod, haddock and halibut was 40.6, 67.2 and 30.7% respectively, however, NL lipid made up the major fraction (88.1–97.1%) of total lipid. Halibut muscle lipid content (8%) was significantly higher than that of the gadoid fish and NL constituted 75.1 and 88.1% of muscle and liver lipid respectively. In all three fish species, liver fatty acid composition mirrored that of the diet. The FAME profiles of muscle, liver and their neutral and polar fractions from cod, haddock and halibut will be presented. Polar lipid classes further separated by HPTLC will also be discussedConclusions:As lean fish, cod/haddock deposited lipid mostly in their liver, whereas halibut stored lipid in both liver and muscle.Haddock and halibut liver indicated de novo synthesis of DHA from EPA or the fish selectively consumed EPA and accumulated DHA in this tissue. Cod liver did not show this ability.Cod and haddock muscle contained more cholesterol than halibut muscle.Gadoid fish, such as cod and haddock, muscle did not store energy in the same way as halibut muscle.Fatty acid profile of neutral lipid from fish liver reflected that of the diet.Cod and halibut showed a similar fatty acid composition for PC, PE, PI from the phospholipid fraction for both liver and muscle.