# New Light on an Old Story: Lymphocystis Disease in Copperband Butterflyfish (Chelmon rostratus) and Orbicular Batfish (Platax orbicularis)

## TL;DR

This study identifies lymphocystis disease virus in two new fish species, using both microscopy and molecular techniques to describe its effects and characteristics.

## Contribution

The study reports LCDV in copperband butterflyfish and identifies a novel LCDV species in orbicular batfish.

## Key findings

- LCDV was identified in copperband butterflyfish using morphological and molecular methods.
- A novel LCDV species was discovered in orbicular batfish through phylogenetic analysis.
- Viral replication and assembly were observed in intracytoplasmic inclusion bodies of infected cells.

## Abstract

Although the clinical course and pathogenesis of lymphocystis disease virus (LCDV) infection have been extensively described in freshwater and seawater environments, lymphocystis disease has not been studied in the copperband butterflyfish (Chelmon rostratus) or described at the molecular level in orbicular batfish (Platax orbicularis). The present study aimed to identify LCDV in a copperband butterflyfish and an orbicular batfish using light and electron microscopy (morphological) and molecular methods, namely PCR followed by phylogenetic analysis. We present a case series of two representatives of two distinct fish species with stress-induced chronic LCDV infection, which presented with typical, recurring, macroscopically visible lymphocystis nodules on their pectoral, caudal, and dorsal fins. After collecting lymphocystis nodules from live animals using skin scraping, we processed the hypertrophic giant cells for qualitative analysis using light and electron microscopy. Through our qualitative morphological analysis, we also share intimate observations of putative viral replication and assembly in the intracytoplasmic inclusion bodies of lymphocystis nodules. We present LCDV infection in a novel species, the copperband butterflyfish, and our molecular analysis identified the virus from the orbicular batfish as a novel LCDV species.