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Molecular epidemiology of Megalocytivirus in freshwater angelfish (Pterophyllum scalare) from
Malaysia

1 Che Azarulzaman Che Johan , Muhd Danish Daniel Abdullah, Sharifah Noor Emilia Syed Jamil
* 1,2
1
Fadaak, Sandra Catherine Zainathan
1,2

1 Faculty of Fisheries and Food Science, Universiti Malaysia Terengganu, 21030 Kuala Nerus,
Terengganu, Malaysia.

2 Institute of Marine Biotechnology, Universiti Malaysia Terengganu, 21030 Kuala Nerus,
Terengganu, Malaysia.

* Corresponding author: z_azarul@yahoo.com

Abstract

Malaysia has more than 630 culturists that are involved in the ornamental fish industry for culturing
250 species including local and exotic species. However, Megalocytiviruses have been associated
globally with severe systemic disease and economic loss in ornamental fish. Thus, this study aimed to
detect the occurrence of Megalocytivirus while discovering its associated risk factors and the genotypes
of its causative agent in an ornamental fish farm in Malaysia. A total of seven pairs of freshwater
angelfish broodstock were used in this study to follow the fish’s life stages from eggs to market size.
The water samples and other samples such as mucus swabs, gill swabs, freshwater angelfish eggs, fries,
juvenile, snail, snail eggs, live feed (tubifex worms and moina), sediment samples and wild fish were
collected periodically for preliminary sampling and from day 0 to day 60. Nested PCR amplifications
were carried out on Megalocytiviruses-related sequences. The phylogenetic tree was inferred from the
major capsid protein (MCP) genes from all known Iridoviridae species using Molecular Evolutionary
Genetics Analysis (MEGA). Pearson’s correlation coefficient values used to determine the strength of
the correlation between the presence of Megalocytiviruses in P. scalare samples and its associated risk
factors. A total of 312 samples out of 935 pooled and individual samples, demonstrated positive results
in tests for the presence of Megalocytiviruses-related sequences except snail eggs and wild fish
(Poecilia reticulata). Detection of Megalocytivirus-associated viruses in water samples demonstrated
evidence of horizontal transmission of the disease. All the nucleotide sequences found in this study had
high nucleotide identities of 88% to 99 % to each other and were closely related with Megalocytivirus
genotype I infectious spleen and kidney necrosis (ISKNV). Overall, this study was the first to confirm
the existence of different possible routes of Megalocytiviruses distribution in the ornamental fish farm
in Malaysia.

Keywords: epidemiology, ISKNV, Megalocytivirus, ornamental fish, risk factors.