First report of infectious spleen and kidney necrosis virus (ISKNV) in two native cichlids cultured in Brazil

Abstract

Peacock bass (syn.: tucunaré, Cichla ocellaris) and the pearl cichlids (syn.: acará, Geophagus brasiliensis) are South American cichlids that are highly valued in both the ornamental and sport fish industries. Since 2017, a number of outbreaks of infectious spleen and kidney necrosis virus (ISKNV) have been reported on Brazilian food and ornamental fish farms. In this study, we detected ISKNV in farmed peacock bass and pearl cichlid by PCR and sequence analysis of the partial major capsid protein (MCP) gene. Moribund peacock bass (n=10) and pearl cichlids (2) from a farm experiencing elevated mortality among juveniles and adults of these species, were submitted for bacteriological and molecular diagnostics. Spleen, liver, brain, and kidney tissues were cultured on 5% sheep blood agar and cystine heart agar with 1% glucose and bovine haemoglobin. No bacteria were isolated from the 12 fish. Additionally, DNA extracts from the liver and spleen of all animals were tested for ISKNV using two conventional polymerase chain reaction (cPCR) assays and two nested PCR (nPCR) assays. ISKNV DNA was amplified in all 12 fish DNA extracts tested, in two or more of the PCR assays. Selected ISKNV amplicons were confirmed by Sanger sequencing. The nucleotide sequences derived from these animals were identical to ISKNV strains previously detected in food (e.g., tilapia and carp) and ornamental species, including strains previously detected in fish from Brazil. To the authors’ knowledge, this is the first report of ISKNV in these native Brazilian cichlids.