Effect Of Dietary Astaxanthin On Growth,Physiology,Body Color,Transcriptome And Metabolome Profiling Of Juvenile Blood Parrotfish(Vieja Melanurus ♀ × Amphilophus Citrinellus ♂)

To investigate the effect of the presence and absence of dietary astaxanthin on growth,body color,biochemical parameters,histological characteristics,transcriptome,and metabolome profiling blood parrotfish juveniles with an initial body weight of 10.16 ± 0.38 g were assigned to three groups:(1)Control(CL),fed a diet without astaxanthin supplementation for 12 weeks;(2)Coloration(ASTA+),fed a diet containing 0.45 g/kg synthetic astaxanthin for 12 weeks;(3)Decoloration(ASTA-)fed the diet supplemented with astaxanthin for the first 6 weeks and then the control diet for the other 6.The weight gain rate and specific growth rate showed no significant difference between ASTA+ and CL at weeks 3 and 6 and among ASTA+,ASTA-and CL at weeks9 and 12.The ASTA+ group showed higher skin redness at weeks 3,6,9,and 12 and higher yellowness at weeks 6,9,and 12 than CL,and ASTA-at week 12.The ASTA+ group had higher concentrations of astaxanthin,HDL-C and LDL-C than the CL at weeks 3,6,9,and 12 and then ASTA-group at weeks 9 and 12.The concentration of pigment cells was higher in the ASTA+group followed by ASTA-and absent in CL at week 12.In addition,muscular thickness and villus height were significantly increased(P < 0.05)along the anterior-intestine,mid-intestine,and posterior-intestine at week 12.Furthermore,kupffer cells along the portal vein lining sinusoids were highly produced in the ASTA+ group than in the CL and ASTA-group.In contrast to the CL and ASTA-,more red pulp of the spleen was present in ASTA+ which indicates the removal of worn-out erythrocyte cells.Astaxanthin concentration was higher in the intestine,liver,and skin of the ASTA+ than in ASTA-and CL at weeks 9 and 12,respectively.Furthermore,skin astaxanthin,high-density lipoprotein cholesterol and low-density lipoprotein cholesterol increased.By comparing ASTA+ and ASTA-with CL,a total of 4250 differentially expressed genes(DEGs)were detected.Pathways,e.g.,PPRA signaling pathway,fatty acid degradation,and ABC transporters,of DEGs involved in carotenoid deposition were enriched.DEGs involved in absorption and transport(e.g.,upregulated lpl and pltp,and downregulated stard7),metabolism(e.g.,upregulated adh1 and dhrs7 cb,and downregulated cyp7b1,dhrs11,and si:ch211-113j14.1),and deposition of carotenoids(e.g.,downregulated apoa1 b and apodb)might be associated with skin coloration.Similarly,a total of 2007 metabolites were identified.OPLS-DA distinctly differentiated the skin metabolites between the coloration and decoloration group of blood parrotfish.Metabolites,including astaxanthin,all-trans-4-ketoretinoic acid,octadecanoic acid,myristic acid,1-oleoyl-2-myristoyl-sn-glycero-3-phosphocholine,(+)-.alpha.-tocopherol,and linoleic acid increased significantly in coloration group while prostaglandin i2,Pc 38:7,N-tetracose-noyl-4-shingenine,lauroyl-1-carnitine,and(z)-5,8,11-trihydroxyoctadec-9-enoic acid were decreased in decoloration group.Further analysis of the KEGG pathway showed significant changes in pathways such as ABC transporters,biosynthesis of amino acids,protein digestion and absorption,aminoacyl-t RNA biosynthesis,glycine,serine,and threonine metabolism were highly enriched in the coloration group whereas galactose metabolism,D-arginine and D-ornithine metabolism,taurine and hypotaurine metabolism were significantly enriched in decoloration group.This is the first time three pathways showing the integration of transcriptomic and metabolomic mechanisms underlying the color formation of juvenile blood parrotfish were established.Overall,the results of this study could help us to understand the physiology and molecular mechanism of body coloration and decoloration under the presence and absence of dietary astaxanthin in blood parrotfish.