Judgment on the degree of fatty liver in different color livers for edible grass carp,Ctenopharyngodon idella

Abstract

The degree of fatty liver in different color livers for edible grass carp(Ctenopharyngodon idella) was discussed.Liver moisture was determined by freeze-drying method,and liver crude fat was measured gravimetrically after ether extract using Soxhlet method.The hepatocyte lipid droplets were observed by light microscopy in oil red O staining for frozen sections.Based on the criterion of human's fatty liver,the degree of fatty liver in edible grass carp was then determined by the positive area ratio.Compared with normal livers of grass carp,the moisture contents of motley livers,blushing livers and yellowing livers were decreased by 6.30%,10.01% and 14.17%(P0.05),respectively;the crude fat contents were increased by 198.25%,331.00% and 485.59%(P0.05),respectively;the number of hepatocyte lipid droplets were significantly increased with the peak in yellowing livers,and the positive area ratios were 3.92,6.31 and 7.32 times of the normal liver(P0.05),respectively.The degree of hepatocyte fatty degeneration in normal liver,motley liver,blushing liver and yellowing liver was 1.10±0.30,2.30±0.20,3.40±0.50 and 4.00±0.20,respectively.After doing linear regression analysis,liver fat contents(Y) were negatively correlated with its moisture contents(X): Y=-1.089 9X+82.035 7,R2=0.989(P0.01);the positive area ratio(Y) were positively correlated with its crude fat content(X): Y=0.970 2X-0.209 0,R2=0.973(P0.05);the crude fat content(Y) were positively correlated with the degree of hepatocyte fatty degeneration(X): Y=3.662 4X-1.788 6,R2=0.985(P0.01);the positive area ratios(Y) were also positively correlated with the degree of hepatocyte fatty degeneration(X): Y=3.622 4X-2.130 6,R2=0.996(P0.01).These results confirm that the oil red O staining method for frozen sections is suitable for evaluating the degree of fish fatty liver.As a result,according to the positive correlation between the positive area ratio and the crude fat content or the degree of hepatocyte fatty degeneration,it is suggested that the liver in grass carp can be defined as fatty liver when its positive area ratio exceeds 2%.Correspondingly,the degree of fatty liver can be defined as mild when its positive area ratio ranges from 2% to 7%,as medium when ranging from 7% to 12%,and as serious when exceeding 12%.