Application And Evaluation Of Beef Tallow In The Feed Of Juvenile Turbot And Tiger Puffer

With the repaid development of the aquaculture industry,the stable supply of fish oil(FO)has become a major challenge for the aquaculture feed industry.Therefore,there has been an urgent need to reduc the use of fish oil and find alternative terrestrially-sourced oils.Among the many terrestrially-sourced oils,beef tallow(BT)has proved to be a promising alternative oil source.The aim of this research is to investigate the effects of beef tallow replacing fish oil(including different replacement strategies)on the growth performance,energy metabolism,muscle quality and gene expression related to lipid metabolism in two important aquaculture species,turbot(Scophthalmus maximus)and tiger puffer(Takifugu rubripes).1.Effects of FO replacement by different levels of BT on growth performance,fatty acid profile and energy metabolism of turbot.A 12-week feeding trial was conducted to investigate the effects of dietary FO substitution with BT on the growth performance,fatty acid profile and energy metabolism of turbot(average initial weight,19.6g).The control diet contained 6% added FO(of dry matter,Diet FO-C).Beef tallow was supplemented into diet FO-C at a 25% gradient,designated as 25 BT,50BT,75 BT,and 100 BT,respectively.The feeding experiment was conducted in a flow-through seawater system.Each group was randomly assigned to triplicate tanks with 30 fish in each tank.The results showed that that a cubic regression relationship was observed between weight gain and dietary FO replacement level.Although total FO replacement by BT significantly reduced the growth of juvenile turbot,no significant difference was observed between FO-C and 75 BT.Diet BT decreased the whole-body crude lipid content but increased the whole-body moisture and ash contents.Dietary BT regulated the proximate composition of fish tissues in a dose dependent manner.High dietary BT levels did not reduce the n-3 LC-PUFA content(% total fatty acid)in the muscle.Partial FO replacement(25 and 50%)by BT even significantly increased the muscle DHA content.The fatty acid composition of the liver,subcutaneous adipose tissue around the fin,and intestine generally reflected those of the diets.No significant difference was observed in muscle and liver mitochondrial DNA copy number among groups,indicating the similar general energy supply status.Dietary BT significantly reduced the concentration of triacylglycerol,cholesterol and malondialdehyde in the serum.In conclusion,beef tallow can replace 75% added FO(appr.45% of total FO including the residual FO in fishmeal)in the diets of turbot,without reducing fish growth.Dietary BT significantly affected the body and muscle composition.2.Effects of different BT substitution levels for FO and different substitution strategies on growth performance,fatty acid profile and genes expression related to lipid metabolism of tiger puffer.A 12-week feeding experiment was conducted to evaluate the effects of FO replacement with BT on tissue proximate composition,fatty acid composition and the expression of lipid metabolism genes of tiger puffer(Takifugu rubripes).Two replacement strategies were used: a standard Graded Dietary Replacement of FO with BT(GDR strategy)and Alternate Feeding between FO-and BT-based Diets(AFD strategy).The positive and negative control diets were formulated with 6% FO(FO-C group)or BT(BT-C group)as the sole added lipid source.In the GDR strategy,three experimental diets were formulated,with 25,50,and 75% of the added FO in the FO-C diet replaced with BT,named 25 BT,50BT,and 75 BT,respectively.In the AFD strategy,alternated feeding patterns between the FO-C and BT-C diet,namely,1,2,and 3 weeks with BT-C followed by 1 week feeding with FO-C(1BT-1FO,2BT-1FO,and 3BT-1FO,respectively),were applied.Each diet or feeding strategy was allocated to triplicate tanks.The results showed that dietary BT inclusion reduced the contents of LC-PUFA in both muscle and liver(edible tissues for this species)of the experimental fish,and the liver displayed a more drastic decrease than the muscle.The trend was consistent between the LC-PUFA content and decreasing dietary FO levels in the GDR strategy.However,in the AFD strategy,a linear relationship was not observed between the LC-PUFA content and the FO feeding duration.The 3BT-1FO treatment resulted in higher LC-PUFA content than 2BT-1FO.When comparing two strategies with the same final FO administration level,namely,50 BT vs 1BT-1FO,and in particular,75 BT vs 3BT-1FO,the AFD strategy resulted in higher LC-PUFA contents in both muscle and liver than the GDR strategy.Although the variations in gene expression were comparatively mild,some changes were worth discussion.Dietary BT inclusion up-regulated the expression of vlc,acox3,acaa1 and mgll,which are key genes of glyceride hydrolysis and fatty acid β-oxidation,and downregulation the expression of glyceride biosynthesis gene dgat1 in the liver.The present result suggested that the 14-18 C fatty acids in BT could be efficiently β-oxidized in the liver,and the triacylglycerol may be better utilized.In conclusion,when FO was replaced with BT in the diets,alternate feeding between FO-and BT-based diets resulted in higher LC-PUFA content than the standard direct replacement.Three weeks feeding with BT-C followed by one week feeding with FO-C appeared to be a good alternate feeding pattern.This study provided a promising strategy of FO sparing in fish farming when the LCPUFA were maintained as high as possible.3.Effect of BT and FO as lipid sources in diet on the composition of volatile compounds in marine lean fish species,turbot and tiger puffer.The concentration of volatile compounds in fish fillet is a key quality indicator.Many volatile compounds are metabolites of fatty acids,and thus could be readily regulated by dietary lipid sources.Gas chromatography-ion mobility spectrometry(GCIMS),a simple and efficient analysis method for volatile compounds,is currently less used in fish.In this experiment,the differences of volatile components in turbot and tiger puffer muscle using BT and FO as feed lipid sources were evaluated using GC-IMS and electronic nose(E-nose).The results are as follows: GC-IMS detected 64 compounds and verified 40 compounds.The main components contained aldehydes(21),alcohols(8),ketones(6),esters(4)and furan(1).Higher abundance of 2-pentanone appeared in the muscle of BT group of both species,in addition to relatively high abundance of 2-methylbutanal and 2-butanone monomer in 100 BT group of turbot.The PCA analysis and Euclidean distance analysis showed that the volatile compounds in the fillets of BT and FO groups of both fish species were significantly different.The E-nose was tested only with the fillets of tiger puffer.The main variations in the volatile compound profile of the fillets from the BT and FO groups were ethanol and alkanes.The experimental results revealed that the effect of BT on muscle volatile profile was complex,and BT reduced the amount and content of aldehydes and alcohols produced by oxidation of n-3 and n-6PUFA in the muscles of turbot and tiger puffer.