φHSIC is a pseudotemperate phage that infects Listonella pelagia, isolated from Mamala Bay, Oahu, Hawaii. φHSIC has a circularly permuted genome 37, of length 966 nt, containing 47 putative open reading frames (ORFs). The pseudolysogenic interaction results in sigmoidal growth curves yielding simultaneous production of high host and phage abundances. The purpose of the present study was to determine patterns of phage gene expression in response to conditions that favor lytic or lysogenic interactions. To evaluate the gene expression patterns of this phage, macroarrays were generated by dotting PCR amplicons of each ORF onto a filter membrane. Viral gene expression over the course of an infection cycle was examined, as was gene expression in the HSIC-1a pseudolysogen grown at normal (39 ppt) and low (11 ppt) salinity. Viral gene expression was significantly higher in the 39 ppt treatment in 2 experiments for nearly every ORF. Free phage and intracellular phage concentrations were significantly lower in the 11 ppt treatment. The results of these experiments indicate that changes in environmental conditions, such as lowered salinity, favor a lysogenic-like relationship in the HSIC-1a pseudolysogen by modulating phage gene expression. These experiments have provided a window into the expression of φHSIC phage genes in response to environmental changes, and may be a model for how phages and their hosts respond to changing conditions in the marine environment.