Henneguya setiuensis

Type host: barramundi, Lates calcarifer (Bloch 1790).

Description of spores: Spores symmetric, with two equal caudal appendages, fusiform sporebody, two equal-sized pyriform polar capsules (Fig. 1). Spore wall thin (0.3 – 0.4 μm), smooth and composed of two equal valves. Apical end of spore body blunt, caudal end tapered and extends into the caudal appendages. Fresh myxospores 36 – 41 μm long, spore length 8.9 ± 0.4 (8.3 – 9.5) μm, width 5.9 ± 0.3 (5.8 – 6.0) μm and thickness 4.1 ± 0.1 (4.1 – 4.2) μm. Two polar capsules, pyriform, blunt at the posterior end and taper anteriorly, length 3.3 ± 0.2 (3.1 – 3.5) μm and width 2.1 ± 0.1 (2.0 – 2.2) μm. Polar tubules coiled in 6 turns perpendicular to the long axis of the polar capsules. Sporoplasm binucleate with a small iodinophilous vacuole. Caudal appendages straight, tapering, 30.5 ± 1.6 (28.0 – 32.0) μm. Plasmodia spherical, diameter 50 – 75 μm.

Remarks: We identified H. setiuensis n. sp. as a new species based on host, site of development (intra-lamellar in gills), morphology and morphometrics. The spores were most similar morphometrically and by tissue tropism (gill) to a previously described species H. latesi Tripathi 1952, from barramundi in India; however, the description of this earlier species has limited informative characters for comparison of spore measurements, and no 18 S rDNA sequence data (Table 2). From the limited data available for comparison, H. setiuensis n. sp. was distinct in spore body shape (rounder vs oval), total length (36 – 41 μm vs 26 – 36 μm) and spore thickness (4.1 μm vs 5.4 μm). Determination of whether H. latesi represents a taxon distinct from any that we observed in Malaysian barramundi would require rediscovery of parasite material from the type locality in India, with molecular and fine-scale tissue tropism observations. Compared with Henneguya spp. known from Lates species hosts, H. setiuensis n. sp. was unique in most dimensions (Table 2) and had the smallest plasmodia; however molecular data and specific tissue site of infection are not available for these other species for more precise comparison. H. setiuensis n. sp. was morphometrically similar to the other two species found in the same fish in the current study, except spore width, polar capsule width and plasmodium size, but distinguishable based on fine-scale tissue tropism and DNA sequence. Molecular analysis: Our consensus 18 S rDNA sequence of 1708 bp was shown by BLAST search to be most similar to other Henneguya species in GenBank, but all <89 %. Pairwise comparison showed H. setiuensis n. sp. to be no more than 91 % similar to the other Henneguya species found in the same fish: 89.9 %, p - distance 0.101 with H. calcarifer n. sp.; 90.1 %, p - distance 0.099 with H. voronini n. sp. Histology: Plasmodia observed in different parts of the gill filaments, inside the multilayered epithelium between lamellae (Fig. 4 a – b). Only local damage of the lamellae was observed, with no gross pathology of the gill filaments.

Locality: Setiu Wetlands, Terengganu, Malaysia.

Etymology: The species is named after the collection location, Setiu Wetlands, Malaysia.

Vouchers: Digital images of syntype spores and histological sections deposited in the parasitological collection of the Zoological Department, Hungarian Natural History Museum, Budapest, collection no. HNHM- 71892. The 18 S rDNA sequence was deposited in GenBank under accession number MH 743111.