First molecular evidence of Thelohanellus wallagoi Sarkar, 1985 (Myxozoa) from economically important food fish, freshwater shark Wallago attu (Siluridae) in India

Abstract

The freshwater shark Wallago attu (Bl. and Schn.) is a frequent silurid in the River Ganga and one of the most commercially exploit fish in India. In a survey on its infection with myxosporeans, spore type belongs to Thelohanellus species was found in the gills, kidney and intestine respectively. Through morphological and molecular investigations, we identified the spore as Thelohanellus wallagoi Sarkar, 1985. They were pyriform in valvular view and slim in sutural view, and had one pyriform polar capsule with four to five turns. The spores measured 8.0 × 4.0 × 2.3 μm. T. wallagoi developed in small cysts in the gill lamellae, whereas cyst and scattered spores of T. wallagoi were also found in the kidney and intestine respectively. The 18S rDNA sequence of T. wallagoi isolates recovered from gills, kidney and intestine were found similar to each other and differed from any other Thelohanellus species available in GenBank and validated its status after 32 years of original description. Phylogenetic analysis signified that T. wallagoi was placed sister to Myxobolus species in the clade that indicated the polyphyletic nature of the genus Thelohanellus.

The occurrence of known Myxobolus and Thelohanellus species (Myxozoa, Myxosporea) from Indian major carps with the description of Myxobolus bandyopadhyayi n. sp. in West Bengal

“…Unfortunately, the majority of the Indian myxosporean species have been poorly described: they are characterised only by morphometrical measurements and by the shape of spores and polar capsules, and less information is provided about the location of plasmodia in infected tissues. The validity of several Indian myxosporean species has recently been supported by molecular biological data ( Székely et al, 2015 ; Chaudhary et al, 2018 , 2019 ; Gupta et al, 2018 ). Presumably, more in-depth investigations supplemented with sequence data might prove several species to be synonyms.…”

“…However, the description of only a part of these species has been complemented with molecular data, therefore it might be possible that several synonymous species exist among them. Gupta et al (2021) mention 40 species of myxobolids with sequence data based on only a limited number of research studies ( Singh and Kaur, 2012 ; Kaur, 2014 ; Rajesh et al, 2014 ; Abraham et al, 2015 ; Székely et al, 2015 ; Chaudhary et al, 2018 , 2019 ; Gupta et al, 2018 ). Myxozoan samples were obtained from the genera Labeo , Gibelion and Cirrhinus collected from West Bengal fish farms and local fish markets which showed signs of myxosporean infections.…”

Molecular tools for identification and classification of Myxozoan parasites (Cnidaria: Myxosporea) in India: Current status

“…Therefore, in myxobolids taxonomy, the molecular analysis should be in congruence with morphological characteristics that can verify and offer great independent evidence relevant for phylogenetic based systematics. Several studies show that phylogenetic analysis with some molecular markers more reliable and consistent over morphological taxonomic features (Palenzuela et al, 2002;Gupta et al, 2018;Kosakyan et al, 2019). In India, identification of myxosporean parasites through molecular tools is at its initial stage as several workers have reported these parasites using morphological classical taxonomic tools.…”

“…Approximately 300 species of myxobolids have been reported till date from India (Kaur and Singh, 2012). Myxobolids fauna has been investigated by a limited number of researchers in India (Gupta et al, 2018;Chaudhary et al, 2019). Many of the reported species have been identified and described solely on the basis of spore morphology.…”