Abstract
Examination of 35 barramundi (Lates calcarifer) from aquaculture cages in Setiu Wetland, Malaysia, revealed a single fish infected with three Henneguya spp. (Cnidaria: Myxosporea). Characterization of the infections using tissue tropism, myxospore morphology and morphometry and 18S rDNA sequencing supported description of three new species: Henneguya setiuensis n. sp., Henneguya voronini n. sp. and H. calcarifer n. sp. Myxospores of all three species had typical Henneguya morphology, with two polar capsules in the plane of the suture, an oval spore body, smooth valve cell surfaces, and two caudal appendages. Spores were morphometrically similar, and many dimensions overlapped, but H. voronini n. sp. had shorter caudal appendages compared with H. calcarifer n. sp. and H. setiuensis n. sp. Gross tissue tropism distinguished the muscle parasite H. calcarifer n. sp. from gill parasites H. setiuensis n. sp. and H. voronini n. sp.; and these latter two species were further separable by fine-scale location of developing plasmodia, which were intra-lamellar for H. setiuensis n. sp. and basal to the filaments for H. voronini n. sp. small subunit ribosomal DNA sequences distinguished all three species: the two gill species H. setiuensis n. sp. and H voronini n. sp. were only 88% similar (over 1708 bp), whereas the muscle species H. calcarifer n. sp. was most similar to H. voronini n. sp. (98% over 1696 bp). None of the three novel species was more than 90% similar to any known myxosporean sequence in GenBank. Low infection prevalence of these myxosporeans and lack of obvious tissue pathology from developing plasmodia suggested none of these parasites are currently a problem for barramundi culture in Setiu Wetland; however additional surveys of fish, particularly at different times of the year, would be informative for better risk assessment.
Highlights
Myxosporeans (Cnidaria: Myxosporea) are common, diverse parasites of marine and freshwater fishes (Lom and Dyková 2006)
Remarks: We identified H. setiuensis n. sp. as a new species based on host, site of development, morphology and morphometrics
Discovery of the Henneguya infections in gills was not unexpected, as this organ is a common site of myxobolid infections; H. calcarifer n. sp. is the first myxosporean with a preference for muscle in a species of Lates
Summary
Myxosporeans (Cnidaria: Myxosporea) are common, diverse parasites of marine and freshwater fishes (Lom and Dyková 2006). H. ictaluri Pote, Hanson et Shivaji, 2000, causes proliferative gill disease in cultured channel catfish (Ictalurus punctatus Rafinesque) with up to 50% mortality (Bowser and Conroy 1985; Bosworth et al 2003), and H. lateolabracis Yokoyama, Kawakami, Yasuda et Tanaka, 2003, is the causative agent of fatal cardiac henneguyosis in cultured Japanese seabass (Lateolabrax spp.) (Pote et al 2000; Yokoyama et al 2003). Exposure of the fish host to other stressors can exacerbate disease effects of the parasite, for example, under stressful or aggregated conditions, mortality of 95–100% has been reported in farm-reared channel catfish (Bowser and Conroy 1985; Minchew 1972)
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