A new host record of Sphaerospora epinepheli (Myxosporea: Bivalvulida) occurring on orange-spotted grouper Epinephelus coioides from Thailand: epidemiology, histopathology and phylogenetic position.

In 1991, the first record of Sphaerospora epinepheli was described as a kidney parasite of wild and cultured malabar grouper, Epinephelus malabaricus, along coastlines of Thailand, the Gulf of Thailand and the Andaman Sea. However, the present study detected high infection of this parasite in kidney renal tubes of orange spotted grouper, Epinephelus coioides, collected from Andaman Sea. The highest infection rate of 36.82% was observed during the rainy season in 2009 in Phang-Nga Bay, in the north of Andaman Sea, which is an important grouper production site in Thailand. The biological and histopathological data of the parasite in this new host record are presented. Species classification is described based on morphological data of mature spore and molecular analysis of myxosporean 18S rDNA phylogeny including that of S. epinepheli which infected E. malabaricus. The genetic position of this parasite found in two host species was also studied. The phylogenetic tree analysis of small-subunit rDNA sequences of S. epinepheli from both infected hosts was constructed using two algorithms, maximum likelihood (ML) and Bayesian inference (BI). They were placed in the clustered basal sphaerosporid clade that contain four long SSU rDNA sphaerosporid species including Sphaerospora truttae, Sphaerospora elegans, Sphaerospora ranae, Sphaerospora fugu and Bipteria formosa with strong bootstrap supports. Histopathologically, renal intratubular myxosporean spores were associated with tubulonephosis, tubular necrosis, chronic interstitial nephritis and mimic membranoproliferative glomerulonephritis. This myxosporean parasite appears to be a significant pathogen on the basis of pathological changes in the renal tubules and is highly distributed in orange-spotted grouper.