The genera Preptetos Pritchard, 1960 and Neopreptetos Machida, 1982 are redefined. The following species are described and/or recorded from marine fishes. From the Great Barrier Reef: Preptetos caballeroi Pritchard, 1960 in Naso annula-tus, N. brevirnslris and N. vlamingii·, P. xesuri (Yamaguti, 1940) in Zebrasoma veliferum and Z. scopas; Preptetos cannoni Barker, Bray et Cribb, 1993 in Siganus dolialus and S. fuscescens', Preptetos laguncula sp. n. in Naso unicornis (type-host); P. impar sp. n. in Lutjanus erythropterus (type-host) and L. malabaricus·, Neopreptetos arusettae Machida, 1982 in Pomacanthus semicirculatus·, and N. kurochkini (Toman, 1989) in Chaetodontoplus meredithi. From southwestern Australia: Preptetos rotto sp. n. in Nelusetta ayraudi (type-host), Neosebastes pandus, Oplegnathus woodwardi and Pagrus auratus. The new combination Preptetos trulla (Linton, 1907) (originally Distomum then Lepocreadium) is made and the species Lepocreadium areolatum (Linton, 1900) is considered likely to belong in Preptetos.