The Robert Maltby in the immigration index didn't arrive in Vic., having died at sea 1863 on the "Queen of the South".

I assume your Thomas Karran Maltby is the one on the IGI extracted entry born 10 Nov.1835, bapt Marown, son of Thomas MALTBY & Esther KARRAN?

Government Gazettes, Victoria 1861-1875 have:
MALTBY Thomas Karran 1873 Sandon Parish Victoria (Aus)
MALTBY Thomas Karran 1875 Clare Inn Victoria (Aus)
MALTBY T K 1864 Victoria (Aus)
MALTBY T K 1865 Carisbrook Victoria (Aus)
MALTBY T K 1865 Majorca Victoria (Aus)
MALTBY T K 1872 Carisbrook Victoria (Aus)
MALTBY T K 1875 Goornong Victoria (Aus)
MALTBY T K 1875 Pay Office Castlemaine Victoria

Sue