Molecular and histopathological insights of Amyloodinium ocellatum infection in Maroon Clownfish

Ramudu, Kurva Raghu and Rehman, Saima and Raj, P P and Lincy, M J and Gora, Adnan Hussain and Sharma, S R Krupesha and Hussain, Tanveer and Kalidas, C (2026) Molecular and histopathological insights of Amyloodinium ocellatum infection in Maroon Clownfish. Journal of Livestock Science, 17. pp. 515-523. ISSN 2277-6214

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Abstract

In marine hatchery with clinical signs of distress, including lethargy, in appetence, and rapid respiration were noted in Maroon Clownfish (Premnas biaculeatus). Gross examination revealed a characteristic fine, dusty coating on the skin. Microscopic analysis confirmed the presence of trophonts in gill biopsies, with wet mounts also revealing tomont stages (2-, 4-, and 8-cell stages) indicative of active parasitic reproduction. This indicates the presence of Amyloodinium spp. The infection significantly impaired the respiratory efficiency of the fish due to heavy parasitic load on the gill lamellae. Parasitic Frequency Index (PFI) analysis revealed a prevalence of 50% among the sampled population (n=4), with a high severity score (1), classifying the infection as “common.” Infections were localized to the gills, body surface, and fins. Histopathology of the tissues from moribund specimens revealed epithelial hyperplasia, mucus hypersecretion, mechanical tissue disruption, immune cell infiltration, lamellar fusion, and necrosis. Molecular detection via 18S rRNA gene-based PCR amplification confirmed species level molecular identification as Amyloodinium ocellatum, yielding amplicons of 336 bp and 225 bp in a two-step process. Sequences were submitted to NCBI GenBank under accession numbers PQ932024 and PQ932025. This incident underscores the need for prompt diagnosis and management of parasitic infections in aquaculture settings to minimize mortality and economic loss.

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