The recent “oceanic turn” (Hester Blum, Elizabeth Deloughrey, Chip Callahan) and “new thalassology” in literary and critical studies has been opening new perspectives on our understanding of the environment and the place of humans and animals in it. Still, religious studies has been slow to move in that direction and explore divine agencies traditionally associated with the sea. The study of Japanese religions is no exception, as still very much focused on large urban areas (the traditional sites of political and economic power) and mountains as privileged loci of the sacred. However, recent scholarship has begun to shed new light on sea-based aspects of traditional Japanese approaches to the sacred. An image of the sea as a vast area of religious activities is emerging in increasingly clear lines. According to it, the sea was envisioned as a frontier zone between this world and the otherworld, between humans and supernatural agencies, and was populated by gods, spirits, and divine life forms. We know something about the sea god Ebisu, associated to fishing and seafaring, and the wealth these activities generated. We also know a good deal about the sacred status of whales and whaling as a ritual activity with various ceremonies including funerals for the whales that had been killed. Some of the most ancient Japanese gods are sea deities: Munakata, Sumiyoshi, and Watatsumi. Interestingly, they are all tripartite entities, composed of divine agencies related to different parts of the seascape—either in depth or in surface distance. It is possible that this peculiar structure was related to aspects of fishing and seafaring. This paper will explore the place of marine animals in traditional Japanese religions. Aside from whales, I will present rituals, legends and beliefs associated with a number of representative members of the Japanese ichthyosphere, including salmon (shake), dolphins (iruka), turtles (kame), bonito (katsuo), octopus (tako), and tuna (maguro). Some of the most salient aspects of maritime religiosity, especially in premodern times, are its fluidity, its local basis, and its relative separatedness from land-based religious organizations and rituals; it is therefore hard to provide a systematic account of it. In this paper, I will nevertheless attempt to propose some general aspects and tendencies.