Characteristic Analysis Of Fatty Acids In Wild Freshwater Fish And Their Diet From Poyang Lake

The muscle fatty acids compositions of seven cultured and Poyang Lake’s wild freshwater fish, M. piceus, C. idellus, H. molitrix, H. nobilis, C. auratus, C. carpio, and P. hypophthalmus, were studied, respectively. Besides, the discriptors of the polyunsaturated fatty acids (PUFA) and odd-branched chain fatty acids (OBCFA) linking fish and diet fatty acids compositions in M. piceus, C. idellus, H. molitrix, and H. nobilis were ascertained. Short packed silica gel column chromatography was performed to optimize the production of triacylglycerols (TAG), phosphatidylethanolamine (PE) and phosphatidylcholine (PC) from fish lipid with95%ethanol as mobile phase and high separation efficiency was achieved; then, the refined PE and PC were identified by high-performance liquid chromatography/ultraviolet detector (HPLC-UV). Afterwards, the fatty acids compositions and positional distributions in TAG, PE, and PC of four wild freshwater fish (M piceus, C. idellus, H. molitrix, and H. nobilis) from Poyang Lake were studied. The main results were as follows:1. Compared with the cultured fish, the amounts of total PUFA and total OBCFA in the wild fish were both higher. In all studied species, wild C. carpio had the highest content of total PUFA (39.53%); the contents of18:2n-6in both wild C. auratus and C. carpio were more than27%; wild M. piceus was richest in20:4n-6(11.68%);20:5n-3was highest in cultured H. nobilis, with the level of6.27%; the levels of22:5n-3in both cultured and wild H. molitrix were richer than any other fish, with2.41%, respectively; wild H. nobilis and M. piceus were richest in22:6n-3(12.24%) and total OBCFA(7.65%), respectively. All the fish studied were contained an amount of total conjugated linoleic acids (CLA), with0.28-1.59%for the cultured fish and0.32-2.67%for the wild fish. It is interesting to note that the contents of total PUFA in H. molitrix and H. nobilis are higher than that of some marine fish. The gas chromatography (GC) results revealed that high linear correlations between dietary and fish fatty acids composition were reported for PUFA (r>0.8) and OBCFA(r>0.6), respectively. Fatty acids taken up directly from the diet could be highly retained in the body. The percentages of20:5n-3、22:6n-3、total n-3long chain PUFA (total n-3LCPUFA, C≥20) declined with the order of zooplankton> phytoplankton> spiral shells> aquatic plants, so the contents of these fatty acids decreased with the order of H. nobilis (fed by zooplankton)> H. molitrix (fed by phytoplankton)> M. piceus (fed by spiral shells)> C. idellus (fed by aquatic plants); the percentage of22:5n-6declined with the order of zooplankton (0.91%)> spiral shells (0.83%)> phytoplankton (0.66%)> aquatic plants (not detected), so the contents of22:5n-6decreased with the order of H. nobilis (3.46%)> M. piceus (1.87%)> H. molitrix (1.13%)> C. idellus (0.77%); the percentages of total OBCFA declined with the order of spiral shells (11.27%)> phragmites communis (10.09%)> zooplankton (8.52%)> phytoplankton (3.31%), so the contents of total OBCFA decreased with the order of M. piceus (7.65%)> C. idellus (5.59%)> H. nobilis (5.30%)> H. molitrix (4.96%).2. Short packed silica gel column chromatography was performed to optimize the production of TAG, PE and PC from fish lipids of P. hypophthalmus with low/no toxic solvents. The effects of mobile phase compositions, silica type, sample loading amount and dimension of the glass chromatotube were investigated and high separation efficiency was achieved:500mL95%ethanol to fractionate PE and PC after TAG removed by200mL ethyl acetate,40mm silica gel (54-74um) bed height of the chromatotube with22mm inner diameter (ID), and0.25g sample loading amount at a flow-rate of1.4mL/min. By this procedure,5.13g PE and1.58g PC per100g fish lipids of P. hypophthalmus were obtained, respectively. The refined PE and PC were identified by HPLC-UV with purity over96%. The phospholipids (PL) products obtained in this study with high purity (over96%) are suitably applied in the fields of nutrition, pharmacology and cosmetics.3. For TAG of the four studied wild fish from Poyang Lake, H. nobilis had the highest content of n-3PUFA (32.52%) and the lowest ratio of n-6/n-3(0.26). PL characterized high content of PUFA, which declined in the order of PE> PC> TAG. In the four studied wild fish, total CLA accounted for0.54-2.85%for TAG and0.27-1.48%for PL; total OBCFA accounted for4.19-5.33%for TAG and3.03-4.36%for PL, respectively.The study revealed that the distribution of fatty acids among the sn-positions was not random:for TAG,16:0,18:2n-6,22:5n-6,22:5n-3and22:6n-3preferred position2, wherease18:0,18:1n-9,18:2n-6,18:3n-3,20:4n-6and20:5n-3mainly distributed in positions1and3; for PL,16:0,18:0,18:1n-9,18:2n-6and18:3n-3preferred in position1, whereas LCPUFA,20:4n-6,22:5n-6,20:5n-3,22:5n-3and22:6n-3, mainly distributed in position2. Total monounsaturated fatty acids (total MUFA) and total PUFA preferred in positions1and3and total saturated fatty acids (total SFA) in position2of TAG while total SFA and total MUFA predominated over sh-1-PL and PUFA over sn-2-PL.