Lipases differ from one another with respect to certain properties, and such differences can be very important for various industrial applications. Considering the rapidly developing nature of the relevant industries, there is a need for new lipases with characteristics differing from those of existing enzymes. In this study, a bacterium was isolated from both the surface mucus layer and gills of rainbow trout (Oncorhynchus mykiss) from Giresun, Turkey. The bacterial species was identified based on its morphological and physiochemical properties, and on its 16S rDNA sequence. The qualitative activity of the bacterial lipase was determined on Rhodamine B and Tween-20 agar plates. The lipase was partially purified from the supernatant of bacterial cultures, and then characterized. The bacterial strain was identified as Acinetobacter sp. strain SU15. The enzyme from Asp-SU15 exhibits maximum activity toward p-nitrophenyl dodecanoate (C12) at 40°C and pH 8.0. The specific activity of the lipase was calculated to be 10.059 U·L–1. The molecular mass of the enzyme was determined to be ~62 kDa via SDS-PAGE. However, native-PAGE indicated that the enzyme forms very large active aggregates, with molecular masses exceeding 250 kDa. The catalytic activity of the enzyme is enhanced in the presence of Co2+, Ca2+, and methanol, but is partially inhibited by Ni2+, ethyl acetate, and butanol. Further research could examine possible industrial applications for the lipase from Asp-SU15.