Morphology and Phylogenetic Analysis of Henneguya sp. Infecting the Orange-Spotted Snakehead (Channa Aurantimaculata) from Tamil Nadu, India

Abstract

Purpose

Henneguya sp. is a crucial myxosporean parasite known to cause milky flesh or tapioca disease in the freshwater fish population, leading to heavy mortality. Studies to investigate its host range and to monitor their prevalence in wild and aquacultured fish are necessary.

Methods

The infected orange-spotted snakehead (Channa aurantimaculata) fish samples showing clinical signs such as severe ulceration and open wounds on the mouth and operculum were collected from an ornamental fish-rearing unit in Chennai, Tamil Nadu. The sample was diagnosed with myxosporean infection by microscopic observation, morphological records and DNA sequencing followed by phylogenetic analysis.

Results

The Henneguya infection was identified in C. aurantimaculata for the first time. Necropsy of the infected fish revealed characteristic multifocal whitish-yellow, oval-shaped cysts measuring 3–5 mm in length on the liver and spleen. The wet mount of cysts showed numerous mature Henneguya spores that were uninucleate, elongated, lenticular and ellipsoidal with the bluntly rounded anterior end gradually tapering off to the posterior with a caudal elongation. The spore body measured 12.1 ± 0.9 μm (10.1–14.7 μm) × 7.1 ± 0.6 μm (5.3–8.5 μm) with two slightly unequal pyriform polar capsules of 6.1 ± 0.5 μm (5.1–7.4 )× 2.5 ± 0.4 μm (1.6–3.9) (large); 6.0 ± 0.4 μm (5.2–6.4) × 2.5 ± 0.3 μm (1.7–3.1) (small) and a caudal elongation of 16.1 ± 1.2 μm in length. The parasite was confirmed to be a Henneguya sp. by PCR amplification of SSrRNA followed by gene sequencing. The sequence generated was submitted in the GenBank under accession number PP852214.1 The maximum likelihood analysis revealed that the obtained sequence is a close relative of H. exilis with pairwise sequence variation of 3.3% and a homology of 99.04%.

Conclusion

The findings highlight the potential impact of Henneguya sp. on ornamental fish health, underscoring the need for vigilant monitoring and management in India.