Effect Of Fasting And Dietary N-3HUFA Levels On Body Composition,Fatty Acid Profiles And Biochemical Parameters Of Large Yellow Croaker Larmichthys Crocea

The present study was performed to investigate the effects of fasting and dietary n-3 HUFA level on body composition,fatty acid profiles and biochemical parameters of commercial-size Larmichthys crocea,which will help to understand the nutrients metabolism and physiological adaptability of Larmichthys crocea during fasting period.Base on the results of this study,we evaluated the possibility of using the fasting combined with adujusting dietary n-3 HUFA level to improve flesh quality of farmed Larmichthys crocea.The results of present study will provide theoretical basis for flesh quality manipulating of farmed Larmichthys crocea.The results are summarized as follows:1.Effect of fasting on body composition,muscle fatty acid profiles and biochemical parameters of liver and serum of Larmichthys crocea105 net-cage cultured healthy fish with similar body weight?249.07±7.28 g?were selected for fasting experiment.The muscle,liver and blood were sampled from experimental fish after 0,3,7,14,21,28,35,42 and 49 days of fasting for chemical analysis,respectively.The results showed that moisture and crude ash content of fish muscle increased and crude lipid content decreased during fasting period.The protein content significantly decreased at day 21 of fasting and then remained constant.Saturated fatty acid?SFA?and monounsaturated fatty acid?MUFA?content in muscle showed no significant change?P>0.05?,while the total polyunsaturated fatty acid?PUFA?and n-3 high unsaturated fatty acid?n-3HUFA?contents significantly decreased at the end of experiment?P<0.05?.The content of glucose?GLU?,protein,lipid and metabolic enzymes activities in serum fluctuated decrease with prolongation of fasting,while Na⁺ and Clcontent fluctuated increase.The total antioxidant capacity?T-AOC?,catalase?CAT?and superoxide dismutase?SOD?activities as well as malonaldehyde?MDA?content in liver fluctuated periodically during fasting.The activities of serum enzymes were significant lower at day 49 compared to initial value.These results suggested that Larmichthys crocea main used body lipid as energy source during fasting period.The nutrient metabolism intensity showed wave-like fluctuated and turn weak as fasting time going by.But the immunity and metabolism function of fish were not significantly harmed by long time fasting.Considering the large fluctuation of biochemical parameters in serum and liver of Larmichthys crocea were obseved from 7 d to 21 d and 14 d to 21 d respectively might relate to nutrition metabolism and energy supply.We suggested the duration of fasting for adjusting muscle composition of farmed Larmichthys crocea should be controled?19.48±0.52 ??in 2³ weeks.2.Effect of dietary n-3HUFA levels on body composition,fatty acid profiles and biochemical parameters of serum of Larmichthys crocea during fasting and refeedingFirstly,400 net-cage cultured healthy fish with similar body weight?260.60±4.26 g?were transfer into indoor concrete tanks for 2-week fasting.Then fish were randomly divided into four groups,which fed four kinds of isonitrogenous and isocaloric diets?D1-D4?with different n-3HUFA levels?30.80% ? 24.84% ? 19.92% ? 13.72%?by mixing different proportions of soybean oil and fish oil contained 34.60% of HUFA?The ratio of fish oil to soybean oil were 4:0,3:1,2:2,1:3 for D1-D4,respectively?.The muscle,liver and blood were sampled from experimental fish after 7,14 and 21 days of fasting for chemical analysis,respectively.The results showed that fish fed D1 had significantly higher muscle protein and lower lipid and ash contents compare to that of fed other diets at day 21 of refeeding?P<0.05?.Namely high inclusion level of dietary n-3 HUFA resulted in high protein and low lipid content of fish muscle.The muscle fatty acids profiles were no significantly different among the all groups.That is meaning fatty acids composition of experimental diet did not affect muscle fatty acids composition during 21 d of refeeding.To some extent,fatty acid compositions of fish liver reflect fatty acid compositions of experimental diets.The content of C18: 1,C20:1 and ?MUFA in the liver elevated with the decreasing of dietary n-3HUFA level.The content of C20:5?C22:5?C22:6 and?50?n-3HUFA in liver of fish in D1 and D2 groups were significantly higher compared to that of D3 and D4 groups.There was no significant difference in C20:5 content of fish liver between D1 and D2 group.While C22: 6 and?50?n-3HUFA contents of fish liver in D1 group was significantly higher than that of D2 groups?P<0.05?.NO significant difference was observed in C20:5,C22:5,C22:6 and?50?n-3HUFA content in the liver of fish between D3 and D4 group?P > 0.05?.The activity of AST,ALP,LDH in the serum of fish in D1 group were significantly higher than other groups?P<0.05?.The serum GLU level kept relative stable among the all groups.But Serum protein?TP,ALB,GLB?and lipid?TG,CHOL,HDL?of Larmichthys crocea in D1 and D2 groups were the lowest and had significant difference with other groups?P<0.05?.Fish in D1 group had significant higher serum K⁺,Na⁺ and Cl-content,lower Ca²⁺ content compared to that of other groups.