Oreochromis spp. is one of the most common cultured fish in the 21st century. It has been introduced into over 90 countries, and increasingly worldwide in aquaculture. In Malaysia, due to its high growth rate, Oreochromis spp. were favoured by farmers. Its production increase from 25,199.89 tonnes in 2018 to 27,926.90 tonnes in 2022. Meanwhile, Betanodavirus is a pathogenic virus and causative agent of Viral Nervous Necrosis (VNN) affecting more than 120 species of marine and freshwater farmed fishes. However, the prevention measures against this serious disease are still unknown due to the lack of research and information, particularly on disease development itself. Therefore, the objective of this study is to determine the degree of Betanodavirus infection in Oreochromis spp., under temperature fluctuation as a stress factor. The surrounding temperature was randomly modulated within the range of 18°C to 26°C. In this study, a total of 100 Oreochromis spp. were selected and divided into five different groups with duplicate tanks. There are four different concentrations of Betanodavirus used (104TCID50/ml, 103TCID50/ml, 102TCID50/ml, 101TCID50/ml) that were injected intraperitoneally including phosphate buffer saline (PBS) as control.
Observation of pathogenicity, mortality and clinical signs were carried out for 30 days and TCID50 value was determined. The earliest clinical sign was observed at concentration of 104TCID50/ml at 10 hours post-infection (pi) while erratic swimming was observed at 20 hours pi. Internal clinical signs (Figure 1) such as congested kidney, enlarged spleen and white nodule spleen were observed for highest concentration group (104 TCID 50/mL) at 7 days pi. The highest cumulative mortality was recorded at concentration 104TCID50/ml with 75% mortality rate (Table 1). Data analysis showed that the TCID50 value of Betanodavirus was 8.254 x 102TCID50/ml (Figure 2). Overall, this study showed that Betanodavirus infection does affect the survivability of Oreochromis spp. under temperature fluctuation stress factor.