Host-Parasite Interaction and Phylogenetic of a New Cnidarian Myxosporean (Endocnidozoa: Myxobolidae) Infecting a Valuative Commercialized Ornamental Fish from Pantanal Wetland Biome, Brazil

Abstract

Myxozoans are a diverse group of parasitic cnidarians of wide distribution. A new species, Myxobolus matogrossoensis n. sp., is herein described infecting wild specimens of tetra mato-grosso Hyphessobrycon eques, caught in the Pantanal biome, the world's largest tropical wetland area. Cysts were found in 3 of the 30 examined fishes. Mature myxospores were ovoid in shape in frontal and measured 6.6 ± 0.4 µm (6.2-7.0 µm) in length and 3.5 ± 0.2 µm (3.3-3.7 µm) in width. The two polar capsules were elongated in shape, equal in size and occupying almost half of the myxospore body. They measured 3.3 ± 0.2 µm (3.1-3.5 µm) in length and 1.8 ± 0.1 µm (1.7-1.9 µm) in width. The polar tubules presented three to four turns. Phylogenetic analysis placed the new species within a clade containing myxobolid species from South American characiforms fish and appears as a close species of Myxobolus piraputangae and Myxobolus umidus. Nevertheless, the sequences of the new species and P. umidus and P. piraputangae have a large genetic divergence of 12 and 12.2% in their 18S rDNA gene, respectively. To the best of our knowledge, this is the first report of a Myxobolus species parasitizing the tetra fish mato-grosso, thus increasing our knowledge of cnidarian myxosporean diversity from South America.

Keywords: Brazil; Myxobolus; Pantanal biome; cnidaria; ornamental fish.

Figure 1

Gill lamellae infected with M. matogrossoensis n. sp. (a) Gill filament (Gf) showing three cysts (asterisks) in their lamellae (L). (b) Ruptured cyst (asterisk) evidencing inside large quantity of smaller myxospores. Scale bars = 20 µm.

Figure 2

Mature myxospores of M. matogrossoensis n. sp. stained with Giemsa. (a) Mature myxospore showing two equal-size polar capsules. Scale bar = 5 μm. (b) Myxospore with extended polar tubule. Scale bar = 5 μm. (c) Schematic representation of a mature myxospore. Scale bar = 2 μm.

Figure 3

Phylogenetic tree generated based on 18S rDNA sequences of Myxobolus species and other closely related myxozoan species. Bootstrap values above 60 are indicated.