Epifluorescence imaging is widely used in cell and molecular biology due to its excellent sensitivity, contrast, and ease of implementation. Optoacoustic imaging has been shown to deliver a highly complementary and unique set of capabilities for biological discovery, such as high spatial resolution in noninvasive deep tissue observations, fast volumetric imaging capacity, and spectrally enriched contrast. In this Letter, we report on a hybrid system combining planar fluorescence and real-time volumetric four-dimensional optoacoustic imaging by means of a fiberscope integrated within a handheld hemispherical ultrasound detection array. The in vivo imaging performance is demonstrated by non-invasive visualization of fast contrast agent perfusion through the mouse brain. The proposed synergistic combination of fluorescence and optoacoustic imaging can benefit numerous studies looking at multi-scale in vivo dynamics, such as functional neuroimaging, visualization of organ perfusion and contrast agent uptake, cell tracking, and pharmacokinetic and bio-distribution analysis.