A bacteriophage was isolated together with Vibrio harveyi (VH) 1114 a from a black tiger shrimp-rearing pond in Thailand. By negative staining transmission electron microscopy (TEM), the phage had an icosahedral head (diameter 60-62 nm), a rigid, non-contractile tail (9-10 nm x 100-120 nm) without a collar or terminal fibers and a genome of double stranded DNA of approximately 80 kb as determined by analysis of restriction enzyme digestion fragments. Since these features would place it in the family Siphoviridae, it was tentatively named V. harveyi siphoviridae-like phage or VHS1. VHS1 could also infect two VH reference strains LMD 22.30 and LMD 80.33 (=ATCC 14126) but yielded smaller plaques than with VH1114. The phage tolerated temperatures as high as 60 degrees C for up to 2h and overnight exposure to a broad range of pH. VHS1 lysogens of VH1114 were unstable, contained unaltered VHS1 DNA, were immune to VHS1 lysis and spontaneously released VHS1 in liquid cultures. Approximately 20 kb of the genome has been sequenced and deposited at GenBank but it mostly showed no significant homology with existing sequences in the database.