Characterization of Piscinoodinium sp. associated with epizootics and mortality in non-native and endemic freshwater fish of the Andaman Islands, India

Piscinoodinium is a well-known parasitic dinoflagellate genus that causes epizootics in tropical freshwater fish. This study investigated the first outbreak of Piscinoodinium sp. in freshwater fish of the Andaman Islands, India. The infection was noticed in the non-native fish Betta splendens and Poecilia reticulata, and in the endemic killifish Aplocheilus andamanicus. The infection caused mass mortality in larval, sub-adult, and adult fish. The parasite was identified based on microscopy and molecular characterization. The prevalence, parasite density, and mortality percentage were recorded. Infected fish had numerous trophonts attached on the body surface, gills, fins, and eyes. Infected skin and gills showed degeneration of the epithelial cells and clubbed gills. Small subunit rDNA (955 bp) was amplified from the Piscinoodinium sp. infecting B. splendens, revealing genetic differences between it and Piscinoodinium spp. from the USA and from India.