Before the installation of marine renewable energy devices, fish species and abundance should be examined for selecting the proper site where the effects of the devices on the environment and fish will be as small as possible. Fish species and abundance can be examined in a variety of methods such as a fish finder using an acoustic wave and fishing gears such as a gill net. However, the fish finder cannot specify the species of fish that is sometimes estimated from the experience of fishermen or scientific researchers. Some amounts of fish must be removed from the target sea area in case of using the fishing gear, while the species of fish can be specified. In the present study, an underwater optical video camera is combined with the fish finder using an acoustic wave to specify the species of fish. A circular fish-eye digital video camera is inserted into a waterproof container. A part of the container is made of glass in a dome shape for the circular fish-eye lens. The container is attached to polyethylene ropes and is towed by a fishing vessel. First, the hydrodynamic characteristics of the container was examined by a towing test with the three kinds of towing speed in a water tank. Then the container was towed in the real sea, which is the demonstration site of offshore wind and wave energy developments off Kamaishi of Iwate Prefecture. The depth of the video camera with the container was not constant since the moving speed of the fishing vessel was slow and fluctuating. The image of video camera could be captured successfully together with that of the acoustic video camera, while fish could not be found in both the optical and acoustic measurements in the present investigation. The investigation will be continued, and the effects of transparency of water should be discussed as future works. Also the actual or model fish should be captured by the underwater video camera to evaluate if it can specify the species of fish.