| Exp.1 Effects of dietary sodium chloride on growth and flesh quality of juvenile grass carpTo investigate the effects of adding sodium chloride(Na Cl)in diets on the growth performance and flesh quality of grass carp,five diets were prepared with Na Cl inclusion at 0(control diet),10,20,30,40 g/kg and fed to grass carp with an initial body weight of(12.26±0.03)g.After 60 days of feeding,10 and 20 g/kg Na Cl groups showed the similar growth to the control,while 30 g/kg and 40 g/kg Na Cl groups had lower weight gain and higher feed conversion ratio than the control.No significant differences were observed in flesh proximate composition except ash among all the groups,and the ash content increased with the increasing Na Cl level.The water-holding capacity was significantly decreased by the supplementation of Na Cl except in thawing loss of 10 g/kg Na Clgroup.The inclusion of 10 and 20 g/kg Na Cl increased the total free amino acids contents,but the supplementation of 20,30,40 g/kg Na Cl significantly decreased the contents of free Glu and Asp in flesh.Dietary Na Cl decreased the flesh hardness and the supplementation of 30 and 40 g/kg Na Cl decreased the flesh chewiness,but there was no significant difference in elasticity and recovery among all the groups.In intestinal histology,the villus height and the villus width of 30 and 40 g/kg Na Cl groups were significantly lower than those of the control,and the supplementation of Na Cl significantly increased the muscular thickness.In conclusion,the supplementation of Na Cl(10-40 g/kg)in diet did not improve the growth performance and flesh quality of grass carp.Exp.2 Effects of dietary sodium chloride on growth and flesh quality of adult grass carpTo investigate the effects of adding sodium chloride(Na Cl)in diets on the growth performance and flesh quality of adult grass carp,five diets were prepared with Na Cl inclusion at 0(control diet),10,20,40 and 60 g/kg,and fed to adult grass carp with an initial body weight of(980.3±20.6)g.After 60 days of feeding,no significant differences were observed in growth and flesh proximate composition among all the groups.The inclusion of 60 g/kg Na Cl decreased the total free amino acids contents,and all Na Cl supplemented groups showed significantly lower contents of free Asp in flesh(P<0.05).The muscle fiber density of 40,60 g/kg Na Cl groups was significantly decreased,while muscle fiber diameter increased(P<0.05).The water-holding capacity was significantly decreased by the supplementation of Na Cl(except 10 g/kg Na Cl group),and dietary Na Cl significantly increased the flesh hardness and the flesh chewiness(P<0.05).The intestinal protease of 60 g/kg Na Cl group and amylase of 40,60g/kg group were significantly lower than those of the control group(P<0.05).The muscle potassium ion and chloride ion contents of Na Cl groups were significantly higher than control group,while the serum sodium ion content was significantly lower than control group(P<0.05).There was no significant difference in content of muscle sodium ion,serum potassium ion and chloride ion among all the groups.In conclusion,the supplementation of Na Cl(10-60 g/kg)in diet did not improve the growth performance of adult grass carp,but the flesh texture quality including hardness and chewiness could be promoted by dietary Na Cl.Exp.3 Effects of starvation and flowing water on growth and flesh quality of grass carpTo investigate the effects of starvation and water movement on the growth performance and flesh quality of grass carp,4 groups were prepared as: flowing water with starvation group(FWS)? still water with starvation group(SWS)?flowing water with feeding group(FWF)and still water with feeding group(SWF).A total of 180 grass carp with an initial body weight of(96.7±2.5)g were randomly distributed into12 cages,and the trial lasted for 30 days with three stages of 10 days per stage.As time goes on,the weight of FWS and SWS groups decreased,while the weight of FWF and SWF groups increased.FWS group and SWF group had the lowest and highest body weight at the end of trial,respectively.In terms of muscle composition,the muscle water content of FWS group and SWS groups increased,and the crude lipid content decreased(P<0.05),while the water and crude lipid content of the SWF group increased(P<0.05)with the extension of time.At the 30 th days,the muscle water content of the starved groups were significantly higher,while crude protein content were significantly lower than those of feeding groups(P<0.05).The muscle fiber density of FWS group was significantly higher than other groups(P<0.05),and the muscle fiber diameter of flowing water groups was significantly lower than still water groups(P<0.05).In terms of muscle texture and water-holding capacity,the chewiness of the FWS group increased,while steaming loss decreased(P<0.05);the muscle hardness,chewiness,and steaming loss of the FWF group increased(P<0.05),and the muscle hardness and chewiness of the SWF groups decreased(P<0.05)as time goes on.At the 30 th day,the SWS group had the highest muscle hardness and chewiness(P<0.05).During the whole period,the starving groups showed significantly higher MDA content than the feeding groups(P<0.05),and the CAT activity of in SWS group was significantly lower than that of other groups(P<0.05).In conclusion,starvation can improve the flesh quality of grass carp when fed in flowing water. |
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