Redescription and molecular characterisation of the predatory isopod Tachaea spongillicola Stebbing, 1907 (Isopoda: Corallanidae) infesting the freshwater fish Pangasius silasi from India

Abstract

ABSTRACT Tachaea spongillicola Stebbing, 1907 has not been widely reported and no case is recorded of its potential predation of freshwater fish. The present study reports the occurrence of T. spongillicola preying on freshwater fish Pangasius silasi Dwivedi et al., 2017 (Pangasiidae) and causing detectable mortalities in its new host. The general morphology and appendages of the non-ovigerous female and male specimens of T. spongillicola are redescribed based on the specimens collected from P. silasi. The important characters to distinguish T. spongillicola from other species of the genus include: body less than 2 times as long as wide; pleonite 4 with posterolateral margins extending beyond pleonite 5; terminal segment of maxilliped more elongated; lacinia mobilis of mandible with three-spined lobe, incisor of the mandible with two cusps; inferior distal margin of carpus of pereopods 1–3 extended to propodus, pereonite 1 is as long as pereonite 2. Additionally, we have generated mitochondrial gene sequences (COI) for the isopod and the morphological findings were confirmed with significant genetic divergences and phylogenetic analysis. Tachaea spongillicola may be a potential threat to the upscaling of intensive cage culture to promote aquaculture production.