Observation Of Body Color Development Process And Transcriptomic Study Of Black Spots In The Spotted Scat(Scatophagus Argus)

Fish have colorful body colors,and the complexity of fish body colors is associated with multiple factors,among which genetic factors are the decisive factor regulate the body color development.Spotted scat(Scatophagus argus)is important marine economic fish with both ornamental and edible value.Body color is an important trait determining ornamental and economic value of spotted scat.However,there are no reports on the basic biological research of the body color formation of spotted scat.This study investigate the types and distribution of pigment cells on the body surface of spotted scat,and track the changes in the pigmentation and body color from embryo to adult at different developmental stages by biological microscopy technology.Meanwhile,the submicroscopic structural analysis and molecular mechanism of black spot formation in spotted scat were investigated by transmission electron microscopy and transcriptome sequencing.The main results as follows:1.In this paper,the pigmented cells of fins,scales and skin of spotted scat were observed microscopically and submicroscopically,and the body color values(a*,b*,L*)of the back and abdomen of farmed fish under different light levels were determined by chromometer.The results showed that there are four types of pigment cells in the body color of spotted scat,which are melanocytes,xanthophores,iridophores and erythrophores.The proportion of different pigment cells in the body color surface of spotted scat was different.The results of transmission electron microscopy showed that the number of melanocytes and iridophores were the most abundant and widely distributed in the skin.The key reason for the formation of black spots is the result of the massive aggregation of melanosomes and melanocytes,as well as the large aggregation of iridescent pigmented cells around them and forming a sharply circumscribed boundary.The results of chromatic aberration meter showed that there was no significant difference in the chromatic aberration value of black spots on the back skin under different light conditions,while the brightness value(L *)of non spots on the abdomen skin was significantly different,indicating that the weaker the light,the brighter the abdominal skin.2.In this study,the pigment deposition and body color changes of the spotted scat were observed were six stages: embryonic pigment development,early larvae,latelarvae,juveniles,juveniles and adult fish.It was found that melanocytes occurred earliest in the embryonic development stage,followed by xanthophores and erythrophores,and the iridophores occurred the latest,which were not observed until the late stage of larvae.From the early stage of the larvae to the later stage of the larvae,the body color of the torso of the larvae(0-24 dph)showed an interesting process of first becoming transparent and then black,the whole body of the larvae changes to dark black at 24 dph,and a large number of iridophores appear in the skin at 30 dph.The faintly visible pigment bands evolve into multiple black spots until the juvenile stage formed clear black vertical stripes,and finally the whole change process of body color stable deposition in the adult spotted scat.3.In this study,the black spotted skin,non-spotted skin and caudal fin transcriptomes of spotted scat were comparatively analyzed.The results show that the transcriptomes results showed that a total of 2,357 differentially expressed genes(DEGs)were identified among the three groups,including seven genes related to pigment synthesis and pigmentation,namely tyrp1,mitf,pmel,slc7a2,tjp1,hsp70 and mart-1.GO analysis showed that some proteins related to actin cytoskeleton and cytoskeleton were significantly enriched in black spotted skin.KEGG analysis found that more differential expression genes in tyrosinase metabolism,melanin synthesis,Wnt signaling pathway,and mitogen-activated protein kinase(MAPK)signaling pathway are involved in the formation of black spots in the skin.In summary,this study identified the types of pigment cells and the submicroscopic structure of black spots formation by the body color of spotted scat,and systematically tracked the changes law of the pigment cells and body color of spotted scat from embryonic to adulthood,it provides a reference for the age identification of wild populations of spotted scat,and the transcriptome results will broaden our understanding of the molecular mechanism of important genes of body color and the pathways which related to the formation of pigment patterns,and provide a certain theoretical basis for the molecular breeding of spotted scat.