Eri and yana are Japanese terms for popular and traditional stationary fish traps used along the coast of Lake Biwa. Eri are laid inshore so as to face the lake or lagoons, or placed in the estuaries of rivers flowing into the lake. Today both are used almost exclusively for young ayu (sweetfish) or ayu fry, however, before the early 1970s, these traps were important means to catch various kinds of fish in both the lake and its lagoons. While eri were privatized long ago, yana can still be observed in cooperative or community-based fishing locations such as Kita-funaki in Adogawa Town, Shiga Prefecture. The aim of this paper is to discuss part-time fishermen who supplement their main job in part-time agriculture or other forms of employment, and who are in this respect quite different from the full-time fishermen of Katata in Ohtsu City. In this way, they seek to secure a stable income with less labor and energy input. Speaking analogically, then, we can recognize features of eri and yana in wet-rice farming technology which has similar social aspects. Here, the author discusses the potential nature and implication of their transformation, as well as changes in the context of local folk society. Lastly, from the viewpoints of both biologicaland culturaldiversity and the ownership of resources, the author wishes to warn against the recent trend of over-specialization in the fishing of ayu fry. In these regards, the author recommends the further development of local environmental education and an improvement in the distribution system of ayu fry.