Suspected viral erythrocytic necrosis (VEN) in a juvenile blackbar triggerfish, Rhinecanthus aculeatus, from Lizard Island, Great Barrier Reef, Australia

Abstract

Suspected viral erythrocytic necrosis (VEN) was detected in blood films from an immature blackbar triggerfish, Rhinecanthus aculeatus, captured on a patch reef at Lizard Island, Great Barrier Reef in November 2005, probably the first record of such an infection from Australia. The fish was kept in captivity and sampled intermittently until December 2007. Giemsa-stained blood films showed initially 18% of mature erythrocytes affected by the VEN-like condition, but accompanying erythroblasts appeared free from infection. Erythrocytes with VEN-like bodies were smooth or crenated in outline, while the inclusion bodies were intracytoplasmic, single or paired, round in outline, stained deep magenta and were between 0.5 -1.7 mm across. Bodies associated with clouds of granular material, fine eosinophilic haloes, and distinct pink-stained comet-tails, were also observed. The DNA content of the VEN-like bodies was confirmed by their green fluorescence following acridine orange staining. Infection levels in this fish fell to 0.4% of mature erythrocytes by May 2006 and persisted at this level until December 2007, when the fish died after just over two years in captivity. Squashes of haematophagous, juvenile gnathiid isopods taken from this fish on initial capture, also contained eosinophilic VEN-like bodies within digesting erythrocytes, suggesting that these crustaceans may be vectors of the condition observed.

Fish mucus versus parasitic gnathiid isopods as sources of energy and sunscreens for a cleaner fish

“…The removal of low-density parasites, however, may still be beneficial for such clients, even if the cost is the potential loss of some mucus, particularly if such parasites pose a greater risk than usual. For example, gnathiids likely transmit haemogregarine blood parasites in various fishes, including parrotfishes (Smit et al 2006), and might also be vectors of viral erythrocytic necrosis (Davies et al 2009). Furthermore, the amount of mucus removed by cleaners may be negligible in fishes with a high mucus load.…”

Nocturnal migration reduces exposure to micropredation in a coral reef fish

“…Migrating animals may also benefit through reduced exposure to parasites and micropredators (reviewed by Shaw and Binning 2016). For example, the migratory grounds that birds (Møller et al 2004, Møller andSzép 2011), ungulates (Folstad et al 1991, Ezenwa 2004, insects (Dumont andHinnekint 1973, Bartel et al 2011), and fish (Poulin et al 2012) inhabit seasonally may have fewer or lower density of parasites than the grounds from which they originated, and ticks may increase the benefit of partial migration for European cervids, as tick, Ixodes ricinus (Linnaeus, 1758), density is lower in the migratory summer grazing areas (Qviller et al 2013).…”

Developing an Apicomplexan DNA Barcoding System to Detect Blood Parasites of Small Coral Reef Fishes

“…VEN is distinguishable by the characteristic appearance of acidophilic, intracytoplasmic inclusion bodies and may also produce discernable intraerythrocytic haloes, granules and comet-tails, cause erythroblastosis and may destroy the host cell nucleus. One such infection has been reported from tropical waters infecting a juvenile Rhinecanthus aculeatus (blackbar triggerfish) (Balistidae) collected off Lizard Island (GBR) (see Davies et al 2009). Whether or not the cytoplasmic or intranuclear viral-like inclusions reported during this study are produced by one such virus may only be clarified with fluorescence microscopy, TEM and molecular analysis.…”