||The ISIIS was developed in collaboration between the University of Miami's Rosenstiel School of Atmospheric and Marine Science (RSMAS) and the subsea engineering company, Bellamare, LLC. Funding was provided by the National Science Foundation, NOAA, UNH Large Pelagics Center, and UM Maytag Chair of Ichthyology. ISIIS systems image organisms and particles in-situ as they swim or flow in between its two pods (fitted with a camera and illumination system). The instrument captures images of mostly undisturbed organisms, at a fine spatial and temporal resolution. ISIIS is an underwater imaging system for capturing in situ, real time images of marine zooplankton of relatively low abundance such as fish larvae and fragile gelatinous organisms. ISIIS imaging systems use industrial grade cameras. On towed sleds, they use a line-scan camera creating one single continuous image representing a real slice of the ocean. However, they can also be fitted with a classic area-scan camera if a system is to be used still (underwater monitoring station) or do slow vertical profiles. The ISIIS system utilizes a high-resolution line-scanning camera with a Light Emitting Diode (LED) light source, modified by plano-convex optics, to create a collimated light field to backlight a parcel of water. The imaged parcel of water passes between the forward portions of two streamlined pods (UW housings), and thereby remains unaffected by turbulence. The resulting very high-resolution image is of plankton in their natural position and orientation. When a sufficient volume of water is imaged this way, quantification of density and fine-scale distribution is possible. ISIIS is capable of imaging a maximum of 162 L of water per second (when flying at 5 knots) with a pixel resolution of 70 um, imaging particles from 1 mm to 13 cm in size.