JAVANESE MEDAKA (Oryzias javanicus, Bleeker 1854) AS A POTENTIAL MODEL ORGANISM FOR STUDY OF STREPTOCOCCOSIS IN FISH

Mohammad Noor Amal Azmai1,*, Siti Suhaiba Mastor1,
Ahmad Ismail1, and Mohd Zamri Saad2
 
1Department of Biology, Faculty of Science, Universiti Putra Malaysia,
43400 UPM Serdang, Selangor, Malaysia.
2Department of Veterinary Laboratory Diagnostics,
Faculty of Veterinary Medicine, Universiti Putra Malaysia,
43400 UPM Serdang, Selangor, Malaysia.
mnamal@upm.edu.my

Javanese medaka (Oryzias javanicus, Bleeker 1854) is a native fish species in Malaysia. It has emerged as a possible new alternative test organism. In this study, we evaluate the capability of Javanese medaka as model organism for study of streptococcosis in fish. Javanese medakas were collected from estuarine area of Sepang, Selangor and were acclimatized to full freshwater environment. The fish were then screened for bacteria and parasites before intraperitoneally challenged with 108 CFU/ml of virulent Streptococcus agalactiae. The clinical signs were observed for 14 days, while dead fish were collected for histological examination and bacterial isolation. The clinical signs included exophthalmia, inflammation at the base of the fins and erratic swimming pattern, while the histopathological changes were mainly generalised congestion of the internal organs. Streptococcus agalactiae were successfully isolated from the dead fish. The clinical signs and histological changes of the infected Javanese medaka were similar as observed in tilapia, the real host of the pathogen. Results showed that Javanese medaka was susceptible towards S. agalactiae infection and could be a potential alternative organism for study of streptococcocis in fish.

Keywords: Javanese medaka, model organism, streptococcosis