mogrunda mogruda can have a yellow base dorsal with a white tip dorsal. Cant really tell much of anything from the pics you posted especialy dealing with a family of fish that have so many almost identical species. I havent heard or seen any such sp volcano in any of my goby research. The one on the rocks favors adspersa they are from volcanic lakes and somtimes when people get fish they souldnt have they make up names like sp volcano. The colorless one on the bottom could be almost any mogruda sp. I say let them settle in take some better pics and try again.