Effects Of Eucommia Ulmoides Oliver Aqueous Extract On Growth,Muscle Quality Of Rainbow Trout(Oncorhynchus Mykiss)

In Guizhou province,fish constitutes an important food source due to its rich nutrient content.Consumers demand healthy,high-quality,natural,and fresh fish products.Rainbow trout（Oncorhynchus mykiss）is an important cold water fish species in gui zhou province.Recently,the quality of muscle from rainbow trout was obviously decreases in intensive culture.Therefore,the search for improving the quality of muscle from fish has been gained increasing interest in the research of aquaculture nutrition.Eucommia ulmoides Oliver,the sole species in the genus Eucommia and family Eucommiaceae,is a deciduous tree indigenous in China and widely cultured in eastern Asian countries.It is highly valued and commonly used in traditional medicines to treat various diseases,especially to relieve hypertension,protect the nervous system,treat diabetics,regulate lipid metabolism,inhibit oxidative stress.The inclusion of E.ulmoides Oliver in diet could improve the flesh quality of some fish.Until now,there has been no scientific report concerning the effect of E.ulmoides Oliver as a supplement in rainbow trout diet to improve flesh quality.Water is a main solvent of decocting medicinal herbs in traditional Chinese medicine.The objective of the present study was to investigate the effects of dietary aqueous extract from E.ulmoides Oliver on the growth performance,flesh quality and myogenic regulatory factors gene expression of rainbow trout,to supply some nutritional strategies for improving the flesh quality of cultured fish.1.Effects of E.ulmoides Oliver aqueous extract on growth,muscular nutrient composition of rainbow troutA 10-week feeding trial was conducted to evaluate the effects of dietary aqueous extract from E.ulmoides Oliver bark on growth and the nutritional composition of rainbow trout（Oncorhynchus mykiss）.The fish with an initial body weight of 145.56±4.12 g were fed one of the five diets,including 0 g kg^-1（control,0%）,5.00 g kg^-1（0.5%）,10.00 g kg^-1（1.0%）,20.00 g kg^-1（2.0%）and 40.00 g kg^-1（4.0%）bark extract.The results showed that:（1）FBW,WG,SGR,HSI,VSI,CF and SR show no significant difference among all treatment（P>0.05）.（2）The muscle lipid of fish in 4.0%was significantly higher than that in other groups（P<0.05）,and fish in 0%showed significantly lower muscle crude lipid content than that in 0.5%,1.0%,and 2.0%groups（P<0.05）.（3）Fish in 4.0%had significantly higher muscle Phe,Gly,Ala,delicious amino acids contents than that in 0%（P<0.05）,and fish in 2.0%had significantly higher muscle Ala content than that in 0%（P<0.05）.（4）Fish in 1.0%showed significantly higher 22:1n-9 content in muscle than that in 0%（P<0.05）.Contents of18:3n-6 in muscle of 0.5%and 4.0%groups were significantly lower than that of 0%group（P<0.05）.Fish in 4.0%had significantly higher 22:5n-3,22:6n-3,andΣPUFA_S n-3 contents than that in other groups（P<0.05）.In conclusion,dietary proper E.ulmoides Oliver aqueous extract supplemental level can improve lipid content,Phe,DAA andΣPUFAS n-3e in muscle and the nutritional value of rainbow trout.The regression model analysis shows that the optimal dietary E.ulmoides Oliver aqueous extract supplemental level which can make rainbow trout acquire the best WGR,SGR,Crude lipid and DAA is 0.75%¹.25%.2.Effect of E.ulmoides Oliver aqueous extract on muscle texture of rainbow troutThe results showed that:（1）There were no significant differences of the pH value in the pH_45min5min and pH_24h4h groups（P>0.05）;The rate of pH decrease in the 2.0%and 4.0%groups was significantly lower than that in the 0%group（P<0.05）;The decrease rate of pH in group 4.0%was significantly lower than that in the 0.5%and 1.0%groups（P<0.05）.（2）The rate of centrifugal water lossand frozen exudation rate had no significant differences among all groups（P>0.05）;Drip loss of the muscle in 1.0%group was significantly higher than that in other groups（P<0.05）.（3）The muscle elasticity and muscle tonicity of the 4.0%group was significantly higher than that of the 0%group（P<0.05）.The muscle adhesiveness and masticability of 4.0%group was significantly higher than that of the 1.0%group（P<0.05）.The muscle cohesion of 4.0%group was significantly higher than that of the 0%,1.0%,2.0%groups（P<0.05）.（4）Fish fed with 1.0%and 4.0%diets had significantly lower muscle fibre diameter than with 0%diet（P<0.05）,the density of muscle fibers increased with the increase of aqueous extract.and fish fed 0%diet had significantly lower muscle fibre density than fish fed other diets（P<0.05）.In conclusion,dietary proper E.ulmoides Oliver aqueous extract supplemental level can lower muscle fibre diameter and increase the density of muscle fibers and muscle elasticity of rainbow trout.The regression model analysis shows that the optimal dietary E.ulmoides Oliver aqueous extract supplemental level which can make rainbow trout acquire the best Chewiness,the density of muscle fibers and muscle fibre diameter is 1.03%².02%.3.Effect of E.ulmoides Oliver aqueous extract on MRFs expression of rainbow troutThe results showed that:The relative expression levels of Myf5,Myf6 and MyoD in the muscles of rainbow trout difference were not significantly（P>0.5）.MyoG expression was significantly higher in the 2.0%groups than in the 0%,0.5%,1.0%and2.0%groups and MyoG expression was significantly higher in the 2.0%groups than in the 0%,0.5%,1.0%.Generally,the above results suggest that adding 2.0%E.ulmoides Oliver aqueous extract to the diet significantly increased the expression of MyoG genes in rainbow trout muscle,thereby improving muscle quality.According to the comprehensive analysis of the indexes,the appropriate addition level of E.ulmoides Oliver aqueous extract in the diet of rainbow trout is 1.03%¹.25%.