Hahella chejuensis is the etiological agent of a novel red egg disease in tilapia (Oreochromis spp.) hatcheries in Thailand

• First report of a novel disease called Hahellosis or red egg disease in tilapia
• Hahella chejuensis, a red pigmented bacterium, was isolated from the red egg samples.
• Challenge tests indicated H. chejuensis caused red egg and reduced hatching rate.
• PCR detection of H. chejuensis from tilapia eggs and gonad tissues was developed.
• In situ hybridization revealed the presence of H. chejuensis in gonads of tilapia

The present study is the first report of a novel disease called Hahellosis or “red egg disease” that has been affecting tilapia (Oreochromis spp.) hatcheries in Thailand. Hahella chejuensis, a red pigmented Gram negative bacterium, was recovered from samples of the red egg and identified to species level based on 99.5%–99.7% nucleotide homology to 16S rDNA of the type strain H. chejuensis KCTC 2396. Experimental infection of eggs indicated that H. chejuensis was able to cause red egg disease and also reduce their hatching. PCR protocols were developed for detection of H. chejuensis in tilapia samples including eggs and ovaries and testes of tilapia broodstocks. Positive signals were obtained in the ovaries and testes of tilapia broodstocks with in situ DNA hybridization using probes specific for H. chejuensis, suggesting possible vertical transmission of the red pigmented bacteria from broodstock to eggs.Statement of relevanceThe authors strongly believe that our manuscript would provide significant knowledge to fish aquaculture especially to that of the tilapia (Oreochromis spp.) hatcheries.