Red Sea Bream Iridovirus (RSIV) Kinetics in Rock Bream (Oplegnathus fasciatus) at Various Fish-Rearing Seawater Temperatures

Abstract

Red sea bream iridoviral disease (RSIVD) causes serious economic losses in the aquaculture industry. In this paper, we evaluated RSIV kinetics in rock bream under various rearing water temperatures and different RSIV inoculation concentrations. High viral copy numbers (approximately 103.7–106.7 RSIV genome copies/L/g) were observed during the period of active fish mortality after RSIV infection at all concentrations in the tanks (25 °C and 20 °C). In the group injected with 104 RSIV genome copies/fish, RSIV was not detected at 21–30 days post-infection (dpi) in the rearing seawater. In rock bream infected at 15 °C and subjected to increasing water temperature (1 °C/d until 25 °C) 3 days later, the virus replication rate and number of viral copies shed into the rearing seawater increased. With the decrease in temperature (1 °C/d) from 25 to 15 °C after the infection, the virus replicated rapidly and was released at high loads on the initial 3–5 dpi, whereas the number of viral copies in the fish and seawater decreased after 14 dpi. These results indicate that the number of viral copies shed into the rearing seawater varies depending on the RSIV infection level in rock bream.

Development of a Propidium Monoazide-Based Viability Quantitative PCR Assay for Red Sea Bream Iridovirus Detection

“…Red sea bream iridovirus was obtained from RSIV-infected rock bream spleen tissue and replicated in the PMF cell line (National Fishery Products Quality Management Service, Busan, Republic of Korea) [ 6 , 46 ]. The PMF cell line was cultured at 25 °C in L-15 medium (Gibco, Billings, MT, USA) supplemented with 10% fetal bovine serum (FBS; Gibco) and 1% antibiotic-antimycotic (A-A; 100 U/mL penicillin, 100 μg/mL streptomycin, and 25 μg/mL amphotericin B, Gibco).…”

“…RSIVD mainly occurs during summer, when temperatures can reach 25 °C, and causes a high mortality of 60–100% in rock bream ( Oplegnathus fasciatus ), a highly susceptible fish species [ 3 , 4 , 5 ]. Recently, a correlation has been found between the progress of RSIV infection in rock bream and the viral load shed into seawater [ 6 ]. The horizontal transmission of infection through water is considered the main route of the spread of RSIV infection in an aquatic environment [ 3 , 7 , 8 ]—the virus particles shed by infected fish can travel through seawater and infect nearby farmed fish [ 9 ].…”

“…The DNA from inactive viruses can serve as a template in qPCR amplification, leading to the overestimation of infectious viruses in diseased fish. Additionally, RSIV-infected fish may continue to shed viral DNA [ 6 ]. However, persistent, positive qPCR results may not necessarily indicate infectivity.…”

Impact of Red Sea Bream Iridovirus Infection on Rock Bream (Oplegnathus fasciatus) and Other Fish Species: A Study of Horizontal Transmission

“…The RSIV strain used in this study was from a previous study [ 8 ]. To generate the crude stock of the virus, the spleen tissue of the rock bream infected with RSIV was homogenized and centrifuged at 10,000× g for 10 min at 4 °C.…”

“…RSIV-infected fishes have been shown to shed the virus into seawater, facilitating horizontal transmission through seawater, which is considered the primary route of RSIV spread [ 1 , 8 ]. The transmission of RSIV among fishes can occur through various routes, including waterborne transmission and direct contact with infected fish.…”