Observations on the biology of Rhabdochona kidderi texensis, a parasite ofNorth American cichlids

An examination of a sample of benthic invertebrates collected from the Uppe r San Marcos River in southwestern Texas, USA in September 1999 revealed th at the nymph of the ephemeropteran Tricorythodes curvatus served as natural intermediate host of the nematode Rhabdochona kidderi texensis (Nematoda: Rhabdochonidae), an intestinal parasite mainly of the Rio Grande perch (Cic hlasoma cyanoguttatum) in this locality; the prevalence of the parasite's t hird- and fourth-stage larvae in mayflies was 6.8% with the intensity of 1- 2 larvae per nymph. Live R. kidderi texensis eggs collected from nematodes recovered from C. cyanoguttatum in Texas were transported to the Czech Repu blic, where they were used to experimentally infect nymphs of the palaearct ic mayfly species Paraleptophlebia submarginata; the development of infecti ve third- and fourth-stage larvae in this experimental intermediate host wa s completed after approximately 10 days at 19 degreesC. Infected nymphs wer e fed to aquarium-reared fishes, four Cichlasoma Nigrofasciatum and one Ore ochromis niloticus, of which only three of the former became infected. The last (fourth) moult of a male nematode was observed in C. nigrofasciatum 23 days p.i. and adult males and gravid females with not fully mature (non-em bryonated) eggs in uteri on days 40 and 51 p.i. The prepatent period of R. kidderi texensis is approximately two months.