Lumpy skin disease of snakeskin gourami: A new record of metacercariae of Posthodiplostomum sp. (Digenea, Diplostomidae) in clinically sick snakeskin gourami, Trichopodus pectoralis Regan, 1910 (Pisces, Osphronemidae)

Abstract

Here, we report on two cases of disease with scattered, pronounced sub-epithelial swellings in the body of cultured snakeskin gourami (Trichopodus pectoralis) fingerlings from two independent farm sites. Locally, the condition is known colloquially as “lumpy skin disease”. The abnormal raised distortions of the skin were due to encysted metacercaria beneath the skin and deeper, within the subcutaneous musculature. Host reaction resulted in a thick, colourless, opalescent wall of the parasitic cyst. Excysted specimens were identified as metacercariae belonging to the genus Posthodiplostomum (Digenea, Diplostomidae) based on a combination of morphology and molecular analysis. Phylogenetically, using SSU rRNA genes, the isolate formed an independent cluster with other unnamed species Posthodiplostomum sp. from snakeheads (Channa spp.) reported from Japan and India; all the parasites in this group had metacercarial cysts with no or few melanophores. The development of parasite cysts resulted in pronounced skin distortions in cultured fingerlings and may be associated with the consequential high rates of morbidity and mortality. This case study is the first report of Posthodiplostomum sp. metacercariae in snakeskin gourami, adding to the growing range of host species infected with the genus. The severity and mortality associated with infection, however, requires further investigation together with a need to identify the precise species present.