Life-Cycle and Biology of Prototransversotrema-Steeri Angel, 1969 (Digenea, Transversotrematidae)

Abstract

A population of Prototransversotrema steeri Angel, 1969 is recorded from the introduced fish Gambusia affinis and the native species Pseudomugil signifer and Mugil cephalus in fresh water in Queensland, Australia. Adults of P. steeri are considerably smaller than adults previously described from marine fish. This appears to be a host-related phenomenon, possibly reflecting the size of the subscale niche offered by the host. The intermediate host is Posticobia brazieri, a hydrobiid snail. It is suggested that different hydrobiid snails may act as intermediate hosts in other parts of Australia. The miracidium develops into a mother sporocyst which produces a single mother redia. Mother rediae produce daughter rediae which may produce further daughter rediae or cercariae. Cercariae emerge from the redia while still embryonic and develop independently in the tissues of the snail. Upon emergence the cercariae attach directly to the definitive host and commence egg-production within 6 days. Gambusia affinis, Xiphophorus rnaculatus, X. helleri, Craterocephalus marjoriae and Mugil cephalus were all infected experimentally. I discuss various theories concerning the phylogenetic position of the Transverso- trematidae within the Digenea and conclude that the family occupies an isolated position not closely allied with any other group.