A Gram-negative, motile, rod-shaped, extremely halophilic archaeon, designated strain HPC1-2(T), was isolated from pla-ra, a salt-fermented fish product of Thailand. Strain HPC1-2(T) was able to grow at 20-60 degrees C (optimum at 37-40 degrees C), at 2.6-5.1 M NaCl (optimum at 3.4-4.3 M NaCl) and at pH 5.0-8.0 (optimum at pH 7.0-7.5). Hypotonic treatment with less than 1.7 M NaCl caused cell lysis. The major polar lipids of the isolate were C(20)C(20) derivatives of phosphatidylglycerol, methylated phosphatidylglycerol phosphate, phosphatidylglycerol sulfate, triglycosyl diether, sulfated triglycosyl diether and sulfated tetraglycosyl diether. The G+C content of the DNA was 65.5 mol%. 16S rRNA gene sequence analysis indicated that the isolate represented a member of the genus Halobacterium in the family Halobacteriaceae. Based on 16S rRNA gene sequence similarity, strain HPC1-2(T) was related most closely to Halobacterium salinarum DSM 3754(T) (99.2%) and Halobacterium jilantaiense JCM 13558(T) (97.8%). However, low levels of DNA-DNA relatedness suggested that strain HPC1-2(T) was genotypically different from these closely related type strains. Strain HPC1-2(T) could also be differentiated based on physiological and biochemical characteristics. Therefore, strain HPC1-2(T) is considered to represent a novel species of the genus Halobacterium, for which the name Halobacterium piscisalsi sp. nov. is proposed. The type strain is HPC1-2(T) (=BCC 24372(T)=JCM 14661(T)=PCU 302(T)).